GHSA-GM3X-23WP-HC2C

Vulnerability from github – Published: 2025-12-08 16:42 – Updated: 2025-12-17 00:44
VLAI
Summary
Path Normalization Bypass in Traefik Router + Middleware Rules
Details

Impact

There is a potential vulnerability in Traefik managing the requests using a PathPrefix, Path or PathRegex matcher.

When Traefik is configured to route the requests to a backend using a matcher based on the path; if the request path contains an encoded restricted character from the following set ('/', '\', 'Null', ';', '?', '#'), it’s possible to target a backend, exposed using another router, by-passing the middlewares chain.

Example

apiVersion: traefik.io/v1alpha1
kind: IngressRoute
metadata:
  name: my-service
spec:
  routes:
    - match: PathPrefix(‘/admin/’)
      kind: Rule
      services:
        - name: service-a
          port: 8080
      middlewares:
        - name: my-security-middleware
    - match: PathPrefix(‘/’)
      kind: Rule
      services:
        - name: service-a
          port: 8080

In such a case, the request http://mydomain.example.com/admin%2F will reach the backend service-a without operating the middleware my-security-middleware and passing the security put in place for the /admin/ path.

Patches

  • https://github.com/traefik/traefik/releases/tag/v2.11.32
  • https://github.com/traefik/traefik/releases/tag/v3.6.4

For more information

If you have any questions or comments about this advisory, please open an issue.

Original Description### Summary A vulnerability exists in Traefik’s path matching logic that allows attackers to bypass access-control middleware (e.g., blocking rules) by using URL-encoded paths. I found this vulnerability while playing PwnSec CTF 2025 with my team @0xL4ugh ### Details Traefik evaluates router rules before decoding or normalizing the request path, but forwards the request after decoding to the backend service. As a result, routes meant to block access to sensitive endpoints (such as internal, beta, or admin endpoints) can be trivially bypassed. ### PoC Traefik configuration used in this issue : ```[http.routers.flask-router-report-deny] entryPoints = ["web"] rule = "PathPrefix(`/report_note`)" priority = 10 middlewares = ["block-access"] service = "flask-service" [http.middlewares.block-access.replacePathRegex] regex = ".*" replacement = "/blocked" 
The intention is to block all access to /report_note.

However, the following request bypasses the block:
POST /%2freport_note HTTP/1.1 Host: localhost:62814 ``` ### Impact Access Control Bypass: Any endpoint intended to be blocked (e.g., admin/debug/beta APIs) can be accessed by URL-encoding slashes or other characters. This could lead to: - Unauthorized access to restricted endpoints - Execution of protected internal functionality - Potential privilege escalation - Bypass of security policies enforced via Traefik routing rules
Severity
6.9 (Medium)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
Show details on source website
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "1.7.34"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.11.32"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.6.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2025-66490"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-436"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2025-12-08T16:42:30Z",
    "nvd_published_at": "2025-12-09T01:16:55Z",
    "severity": "MODERATE"
  },
  "details": "## Impact\n\nThere is a potential vulnerability in Traefik managing the requests using a `PathPrefix`, `Path` or `PathRegex` matcher.\n\nWhen Traefik is configured to route the requests to a backend using a matcher based on the path; if the request path contains an encoded restricted character from the following set **(\u0027/\u0027, \u0027\\\u0027, \u0027Null\u0027, \u0027;\u0027, \u0027?\u0027, \u0027#\u0027)**, it\u2019s possible to target a backend, exposed using another router, by-passing the middlewares chain.\n\n## Example\n\n```yaml\napiVersion: traefik.io/v1alpha1\nkind: IngressRoute\nmetadata:\n  name: my-service\nspec:\n  routes:\n    - match: PathPrefix(\u2018/admin/\u2019)\n      kind: Rule\n      services:\n        - name: service-a\n          port: 8080\n      middlewares:\n        - name: my-security-middleware\n    - match: PathPrefix(\u2018/\u2019)\n      kind: Rule\n      services:\n        - name: service-a\n          port: 8080\n```\n\nIn such a case, the request `http://mydomain.example.com/admin%2F` will reach the backend `service-a` without operating the middleware `my-security-middleware` and passing the security put in place for the `/admin/` path.\n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v2.11.32\n- https://github.com/traefik/traefik/releases/tag/v3.6.4\n\n## For more information\n\nIf you have any questions or comments about this advisory, please [open an issue](https://github.com/traefik/traefik/issues).\n\n\u003cdetails\u003e\n\u003csummary\u003eOriginal Description\u003c/summary\u003e### Summary\nA vulnerability exists in Traefik\u2019s path matching logic that allows attackers to bypass access-control middleware (e.g., blocking rules) by using URL-encoded paths. I found this vulnerability while playing PwnSec CTF 2025 with my team @0xL4ugh\n\n### Details\nTraefik evaluates router rules before decoding or normalizing the request path, but forwards the request after decoding to the backend service. As a result, routes meant to block access to sensitive endpoints (such as internal, beta, or admin endpoints) can be trivially bypassed.\n\n### PoC\nTraefik configuration used in this issue :\n```[http.routers.flask-router-report-deny]\n  entryPoints = [\"web\"]\n  rule = \"PathPrefix(`/report_note`)\"\n  priority = 10\n  middlewares = [\"block-access\"]\n  service = \"flask-service\"\n\n[http.middlewares.block-access.replacePathRegex]\n  regex = \".*\"\n  replacement = \"/blocked\"\n```\nThe intention is to block all access to /report_note.\n\nHowever, the following request bypasses the block:\n```\nPOST /%2freport_note HTTP/1.1\nHost: localhost:62814\n\n\n```\n### Impact\nAccess Control Bypass:\nAny endpoint intended to be blocked (e.g., admin/debug/beta APIs) can be accessed by URL-encoding slashes or other characters.\n\nThis could lead to:\n\n- Unauthorized access to restricted endpoints\n- Execution of protected internal functionality\n- Potential privilege escalation\n- Bypass of security policies enforced via Traefik routing rules\n\u003c/details\u003e",
  "id": "GHSA-gm3x-23wp-hc2c",
  "modified": "2025-12-17T00:44:50Z",
  "published": "2025-12-08T16:42:30Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-gm3x-23wp-hc2c"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-66490"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/traefik/traefik"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v2.11.32"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.6.4"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Path Normalization Bypass in Traefik Router + Middleware Rules"
}



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