{"id":"CVE-2025-54121","aliases":["CLSA-2025-1764115957","CLSA-2025-1764288754","CLSA-2026-1789447406","DEBIAN-CVE-2025-54121","EUVD-2025-22159","GHSA-2c2j-9gv5-cj73","PYSEC-2026-1941","ROOT-APP-PYPI-CVE-2025-54121","SUSE-SU-2025:02544-1","SUSE-SU-2026:22151-1","UBUNTU-CVE-2025-54121","openSUSE-SU-2025:15381-1","openSUSE-SU-2026:20975-1"],"status":"published","title":"Starlette has possible denial-of-service vector when parsing large files in multipart forms","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","severity":{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.0066,"percentile":0.519,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-770"],"published":"2025-07-21T19:34:23Z","modified":"2026-10-28T02:30:56Z","fixes":[{"ecosystem":"PyPI","package":"starlette","fixed_in":["0.47.2"],"sources":["ghsa","osv"]},{"ecosystem":"TuxCare:PyPI","package":"starlette","fixed_in":["0.27.0.post2+tuxcare","0.13.6.post1+tuxcare"],"sources":["osv"]},{"ecosystem":"Debian:12","package":"starlette","fixed_in":["0.26.1-1+deb12u1"],"sources":["osv"]},{"ecosystem":"Debian:13","package":"starlette","fixed_in":["0.46.1-3"],"sources":["osv"]},{"ecosystem":"Debian:14","package":"starlette","fixed_in":["0.46.1-3"],"sources":["osv"]},{"ecosystem":"Root:PyPI","package":"starlette","fixed_in":["0.22.0+aikido.7","0.45.3+aikido.10","0.45.3+aikido.11","0.45.3+aikido.5","0.45.3+aikido.6","0.45.3+aikido.7","0.45.3+aikido.8","0.45.3+aikido.9","0.47.0+aikido.3","0.22.0+aikido.3","0.46.2+aikido.3","0.46.2+aikido.4","0.41.3+aikido.6","0.46.2+aikido.6","0.45.3+aikido.13","0.45.3+aikido.14","0.41.3+aikido.7","0.46.2+aikido.7","0.22.0+aikido.5","0.45.3+aikido.15","0.22.0+aikido.6"],"sources":["osv"]},{"ecosystem":"Root:PyPI","package":"rootio-starlette","fixed_in":["0.22.0+aikido.4","0.45.3+aikido.12","0.46.2+aikido.5","0.47.0+aikido.4"],"sources":["osv"]},{"ecosystem":"openSUSE:Leap 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has possible denial-of-service vector when parsing large files in multipart forms","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","status":"published","published":"2025-07-21T20:06:03.818Z","modified":"2025-07-22T19:54:24.784Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"cna"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:32:27.603809Z"}],"euvd":[{"id":"EUVD-2025-22159","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","status":"published","published":"2025-07-21T20:06:03Z","modified":"2025-07-22T19:54:24Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T20:32:05.325431Z"}],"ghsa":[{"id":"GHSA-2c2j-9gv5-cj73","title":"Starlette has possible denial-of-service vector when parsing large files in multipart forms","description":"### Summary\nWhen parsing a multi-part form with large files (greater than the [default max spool size](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/formparsers.py#L126)) `starlette` will block the main thread to roll the file over to disk. This blocks the event thread which means we can't accept new connections.\n\n### Details\nPlease see this discussion for details: https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403. In summary the following UploadFile code (copied from [here](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/datastructures.py#L436C5-L447C14)) has a minor bug. Instead of just checking for `self._in_memory` we should also check if the additional bytes will cause a rollover.\n\n```python\n\n    @property\n    def _in_memory(self) -\u003e bool:\n        # check for SpooledTemporaryFile._rolled\n        rolled_to_disk = getattr(self.file, \"_rolled\", True)\n        return not rolled_to_disk\n\n    async def write(self, data: bytes) -\u003e None:\n        if self.size is not None:\n            self.size += len(data)\n\n        if self._in_memory:\n            self.file.write(data)\n        else:\n            await run_in_threadpool(self.file.write, data)\n```\n\nI have already created a PR which fixes the problem: https://github.com/encode/starlette/pull/2962\n\n\n### PoC\nSee the discussion [here](https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403) for steps on how to reproduce.\n\n### Impact\nTo be honest, very low and not many users will be impacted. Parsing large forms is already CPU intensive so the additional IO block doesn't slow down `starlette` that much on systems with modern HDDs/SSDs. If someone is running on tape they might see a greater impact.","status":"published","published":"2025-07-21T19:34:23Z","modified":"2025-07-21T22:21:06Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:38:50.834587Z"}],"nvd":[{"id":"CVE-2025-54121","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","status":"published","published":"2025-07-21T20:15:41.827Z","modified":"2026-06-17T09:39:29.22Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium","assessor":"secondary"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T14:11:19.382856Z"}],"osv":[{"id":"CVE-2025-54121","title":"Starlette has possible denial-of-service vector when parsing large files in multipart forms","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","status":"published","published":"2025-07-21T20:06:03.818Z","modified":"2026-10-28T02:30:56.95231595Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:44:50.863921Z"},{"id":"DEBIAN-CVE-2025-54121","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","status":"published","published":"2025-07-21T20:15:41.827Z","modified":"2026-09-01T20:05:54.543399003Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T15:45:47.378563Z"},{"id":"GHSA-2c2j-9gv5-cj73","title":"Starlette has possible denial-of-service vector when parsing large files in multipart forms","description":"### Summary\nWhen parsing a multi-part form with large files (greater than the [default max spool size](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/formparsers.py#L126)) `starlette` will block the main thread to roll the file over to disk. This blocks the event thread which means we can't accept new connections.\n\n### Details\nPlease see this discussion for details: https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403. In summary the following UploadFile code (copied from [here](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/datastructures.py#L436C5-L447C14)) has a minor bug. Instead of just checking for `self._in_memory` we should also check if the additional bytes will cause a rollover.\n\n```python\n\n    @property\n    def _in_memory(self) -\u003e bool:\n        # check for SpooledTemporaryFile._rolled\n        rolled_to_disk = getattr(self.file, \"_rolled\", True)\n        return not rolled_to_disk\n\n    async def write(self, data: bytes) -\u003e None:\n        if self.size is not None:\n            self.size += len(data)\n\n        if self._in_memory:\n            self.file.write(data)\n        else:\n            await run_in_threadpool(self.file.write, data)\n```\n\nI have already created a PR which fixes the problem: https://github.com/encode/starlette/pull/2962\n\n\n### PoC\nSee the discussion [here](https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403) for steps on how to reproduce.\n\n### Impact\nTo be honest, very low and not many users will be impacted. Parsing large forms is already CPU intensive so the additional IO block doesn't slow down `starlette` that much on systems with modern HDDs/SSDs. If someone is running on tape they might see a greater impact.","status":"published","published":"2025-07-21T19:34:23Z","modified":"2026-09-10T03:50:25.704876348Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"cwes":["CWE-770"],"updated_at":"2026-11-02T15:46:34.338541Z"},{"id":"PYSEC-2026-1941","title":"Starlette has possible denial-of-service vector when parsing large files in multipart forms","description":"### Summary\nWhen parsing a multi-part form with large files (greater than the [default max spool size](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/formparsers.py#L126)) `starlette` will block the main thread to roll the file over to disk. This blocks the event thread which means we can't accept new connections.\n\n### Details\nPlease see this discussion for details: https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403. In summary the following UploadFile code (copied from [here](https://github.com/encode/starlette/blob/fa5355442753f794965ae1af0f87f9fec1b9a3de/starlette/datastructures.py#L436C5-L447C14)) has a minor bug. Instead of just checking for `self._in_memory` we should also check if the additional bytes will cause a rollover.\n\n```python\n\n    @property\n    def _in_memory(self) -\u003e bool:\n        # check for SpooledTemporaryFile._rolled\n        rolled_to_disk = getattr(self.file, \"_rolled\", True)\n        return not rolled_to_disk\n\n    async def write(self, data: bytes) -\u003e None:\n        if self.size is not None:\n            self.size += len(data)\n\n        if self._in_memory:\n            self.file.write(data)\n        else:\n            await run_in_threadpool(self.file.write, data)\n```\n\nI have already created a PR which fixes the problem: https://github.com/encode/starlette/pull/2962\n\n\n### PoC\nSee the discussion [here](https://github.com/encode/starlette/discussions/2927#discussioncomment-13721403) for steps on how to reproduce.\n\n### Impact\nTo be honest, very low and not many users will be impacted. Parsing large forms is already CPU intensive so the additional IO block doesn't slow down `starlette` that much on systems with modern HDDs/SSDs. If someone is running on tape they might see a greater impact.","status":"published","published":"2026-07-07T16:02:58.086064Z","modified":"2026-07-07T17:47:58.806073973Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T15:52:55.537808Z"},{"id":"ROOT-APP-PYPI-CVE-2025-54121","title":"CVE-2025-54121 in starlette - Patched by Root","description":"Root has patched CVE-2025-54121 in the starlette package for Root:PyPI. Multiple fixed versions available.","status":"published","published":"2026-09-07T17:47:27Z","modified":"2026-09-07T18:30:03.800460016Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T15:53:27.940619Z"},{"id":"UBUNTU-CVE-2025-54121","description":"Starlette is a lightweight ASGI (Asynchronous Server Gateway Interface) framework/toolkit, designed for building async web services in Python. In versions 0.47.1 and below, when parsing a multi-part form with large files (greater than the default max spool size) starlette will block the main thread to roll the file over to disk. This blocks the event thread which means the application can't accept new connections. The UploadFile code has a minor bug where instead of just checking for self._in_memory, the logic should also check if the additional bytes will cause a rollover. The vulnerability is fixed in version 0.47.2.","status":"published","published":"2025-07-21T20:15:00Z","modified":"2026-10-17T12:58:36.985643615Z","cvss":[{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","level":"medium"}],"updated_at":"2026-11-02T16:55:50.31802Z"},{"id":"CLSA-2025-1764115957","title":"TuxCare security update for starlette (1 CVE)","description":"TuxCare rebuilt starlette to address 1 CVE. Fixed in 0.27.0.post2+tuxcare.","status":"published","published":"2026-08-04T14:52:09Z","modified":"2026-10-15T09:47:53.553887649Z","updated_at":"2026-11-02T15:43:42.847264Z"},{"id":"CLSA-2025-1764288754","title":"TuxCare security update for starlette (1 CVE)","description":"TuxCare rebuilt starlette to address 1 CVE. Fixed in 0.13.6.post1+tuxcare.","status":"published","published":"2026-08-04T14:52:09Z","modified":"2026-10-15T09:47:53.548799191Z","updated_at":"2026-11-02T15:43:42.847264Z"},{"id":"CLSA-2026-1789447406","title":"TuxCare security update for starlette (8 CVEs)","description":"TuxCare rebuilt starlette to address 8 CVEs. Fixed in 0.25.0.post1+tuxcare.","status":"published","published":"2026-09-15T04:43:26Z","modified":"2026-10-15T09:48:01.789333066Z","updated_at":"2026-11-02T15:43:47.938828Z"},{"id":"openSUSE-SU-2025:15381-1","title":"python311-starlette-0.47.2-1.1 on GA media","description":"These are all security issues fixed in the python311-starlette-0.47.2-1.1 package on the GA media of openSUSE Tumbleweed.","status":"published","published":"2025-07-24T00:00:00Z","modified":"2026-02-04T04:35:36.045969Z","updated_at":"2026-11-02T16:58:37.810934Z"},{"id":"openSUSE-SU-2026:20975-1","title":"Security update for python-starlette","description":"This update for python-starlette fixes the following issues\n\n- CVE-2025-54121: denial-of-service when parsing a multi-part form with large files (bsc#1246855).\n- CVE-2025-62727: DoS via Range header merging (bsc#1252805).\n- CVE-2026-48710: Missing Host header validation poisons request.url.path, bypassing path-based security checks\n  (bsc#1266369).\n","status":"published","published":"2026-06-17T08:36:30Z","modified":"2026-06-24T18:24:21.192210178Z","updated_at":"2026-11-02T16:58:41.885092Z"},{"id":"SUSE-SU-2025:02544-1","title":"Security update for python-starlette","description":"This update for python-starlette fixes the following issues:\n\n- CVE-2025-54121: Correctly parse multi-part form with large files to avoid DoS. (bsc#1246855)\n","status":"published","published":"2025-07-29T13:47:48Z","modified":"2026-03-23T04:46:40.345117Z","updated_at":"2026-11-02T15:53:56.647031Z"},{"id":"SUSE-SU-2026:22151-1","title":"Security update for python-starlette","description":"This update for python-starlette fixes the following issues\n\n- CVE-2025-54121: denial-of-service when parsing a multi-part form with large files (bsc#1246855).\n- CVE-2025-62727: DoS via Range header merging (bsc#1252805).\n- CVE-2026-48710: Missing Host header validation poisons request.url.path, bypassing path-based security checks\n  (bsc#1266369).\n","status":"published","published":"2026-06-17T08:36:56Z","modified":"2026-06-24T18:24:16.488365952Z","updated_at":"2026-11-02T15:54:02.654057Z"}]}}