Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when headerField is configured with a non-canonical HTTP header name (e.g., x-auth-user instead of X-Auth-User), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.
{
"cna_assigner": "GitHub_M",
"cwe_ids": [
"CWE-290"
],
"osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/33xxx/CVE-2026-33433.json"
}{
"extracted_events": [
{
"cpe": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "0"
},
{
"fixed": "2.11.42"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*",
"range": [
{
"introduced": "3.0.0"
},
{
"fixed": "3.6.12"
}
],
"source": "CPE_RANGE"
},
{
"cpe": "cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*",
"range": [
{
"introduced": "3.7.0-ea1"
},
{
"last_affected": "3.7.0-ea1"
}
],
"source": "CPE_STRING"
},
{
"cpe": "cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*",
"range": [
{
"introduced": "3.7.0-ea2"
},
{
"last_affected": "3.7.0-ea2"
}
],
"source": "CPE_STRING"
},
{
"original_tag": "v2.11.42",
"range": [
{
"fixed": "e4b2c648bf78b29a97a560571510b61eb7dc67b6"
}
],
"source": "REFERENCES_TAG"
},
{
"original_tag": "v3.6.11",
"range": [
{
"fixed": "33219a0af86c41a8db81d37c444f65172bfb3e35"
}
],
"source": "REFERENCES_TAG"
},
{
"original_tag": "v3.7.0-ea.3",
"range": [
{
"fixed": "9990cfc613835f32d831174bd2d5dea6b2c1e45a"
}
],
"source": "REFERENCES_TAG"
}
]
}