ghsa-fvhj-4qfh-q2hm
Vulnerability from github
Published
2023-12-05 18:11
Modified
2023-12-07 23:06
Severity ?
6.5 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Summary
Traefik incorrectly processes fragment in the URL, leads to Authorization Bypass
Details

Summary

When a request is sent to Traefik with a URL fragment, Traefik automatically URL encodes and forwards the fragment to the backend server. This violates the RFC because in the origin-form the URL should only contain the absolute path and the query.

When this is combined with another frontend proxy like Nginx, it can be used to bypass frontend proxy URI-based access control restrictions.

Details

For example, we have this Nginx configuration:

location /admin { deny all; return 403; } This can be bypassed when the attacker is requesting to /#/../admin

This won’t be vulnerable if the backend server follows the RFC and ignores any characters after the fragment.

However, if Nginx is chained with another reverse proxy which automatically URL encode the character # (Traefik) the URL will become

/%23/../admin

And allow the attacker to completely bypass the Access Restriction from the Nginx Front-End proxy.

Here is a diagram to summarize the attack:

image

PoC

image (1)

This is the POC docker I've set up. It contains Nginx, Traefik proxies and a backend server running PHP.

https://drive.google.com/file/d/1vLnA0g7N7ZKhLNmHmuJ4JJjV_J2akNMt/view?usp=sharing

Impact

This allows the attacker to completely bypass the Access Restriction from Front-End proxy.

Show details on source website

To clipboard 

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.10.6"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.0.0-beta5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2023-47106"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-177",
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2023-12-05T18:11:48Z",
    "nvd_published_at": "2023-12-04T21:15:33Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nWhen a request is sent to Traefik with a URL fragment, Traefik automatically URL encodes and forwards the fragment to the backend server. This violates the RFC because in the origin-form the URL should only contain the absolute path and the query.\n\nWhen this is combined with another frontend proxy like Nginx, it can be used to bypass frontend proxy URI-based access control\nrestrictions. \n\n### Details\nFor example, we have this Nginx configuration:\n\n```\nlocation /admin {\n     deny all;\n     return 403;\n}\n```\nThis can be bypassed when the attacker is requesting to /#/../admin\n\nThis won\u2019t be vulnerable if the backend server follows the RFC and ignores any characters after the fragment.\n\nHowever, if Nginx is chained with another reverse proxy which automatically URL encode the character # (Traefik) the URL will become\n\n/%23/../admin\n\nAnd allow the attacker to completely bypass the Access Restriction from the Nginx Front-End proxy.\n\nHere is a diagram to summarize the attack:\n\n![image](https://user-images.githubusercontent.com/47447167/278849578-34ca0546-99b4-44c8-8fc8-8e799c1f5069.png)\n\n### PoC\n![image (1)](https://user-images.githubusercontent.com/47447167/278849597-280f2e80-f2d7-4dd9-9662-b8f488fd5ff2.png)\n\nThis is the POC docker I\u0027ve set up.  It contains Nginx, Traefik proxies and a backend server running PHP.\n\nhttps://drive.google.com/file/d/1vLnA0g7N7ZKhLNmHmuJ4JJjV_J2akNMt/view?usp=sharing\n\n### Impact\nThis allows the attacker to completely bypass the Access Restriction from Front-End proxy.",
  "id": "GHSA-fvhj-4qfh-q2hm",
  "modified": "2023-12-07T23:06:09Z",
  "published": "2023-12-05T18:11:48Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-fvhj-4qfh-q2hm"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2023-47106"
    },
    {
      "type": "WEB",
      "url": "https://datatracker.ietf.org/doc/html/rfc7230#section-5.3.1"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/traefik/traefik"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v2.10.6"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.0.0-beta5"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Traefik incorrectly processes fragment in the URL, leads to Authorization Bypass"
}


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