{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/cpes/cpe2.3atraefiktraefik3.7.0ea2/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":["cpe:2.3:a:traefik:traefik:*:*:*:*:*:*:*:*","cpe:2.3:a:traefik:traefik:3.7.0:ea1:*:*:*:*:*:*","cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*","cpe:2.3:a:traefik:traefik:3.7.0:ea3:*:*:*:*:*:*","cpe:2.3:a:traefik:traefik:3.7.0:rc1:*:*:*:*:*:*"],"_cs_cves":[{"cvss":8.8,"id":"CVE-2026-33433"},{"cvss":10,"id":"CVE-2026-39858"}],"_cs_exploited":false,"_cs_has_poc":true,"_cs_poc_references":[],"_cs_products":["Traefik","Traefik (v2.11.x \u003c= 2.11.43, v3.6.x \u003c= 3.6.14, v3.7.x \u003c= 3.7.0-rc.2)"],"_cs_severities":["high"],"_cs_tags":["authentication-bypass","header-injection","forwarded-headers","traefik"],"_cs_type":"advisory","_cs_vendors":["Traefik"],"content_html":"\u003cp\u003eA high severity authentication bypass vulnerability exists in Traefik versions before 2.11.43, 3.6.14, and 3.7.0-rc.2, affecting the \u003ccode\u003eForwardAuth\u003c/code\u003e middleware and snippet-based authentication. The vulnerability stems from incomplete sanitization of forwarded headers. Traefik's logic only targets canonical header names like \u003ccode\u003eX-Forwarded-Proto\u003c/code\u003e, failing to strip or normalize alias variants that use underscores instead of dashes (e.g., \u003ccode\u003eX_Forwarded_Proto\u003c/code\u003e). This allows attackers to inject spoofed trust context, such as a trusted scheme or host, through the alias headers. If the authentication backend normalizes underscore and dash header forms equivalently, an attacker can bypass authentication on protected routes without valid credentials. This impacts deployments where authorization decisions rely on forwarded headers.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAn attacker identifies a Traefik instance using \u003ccode\u003eForwardAuth\u003c/code\u003e or snippet-based authentication.\u003c/li\u003e\n\u003cli\u003eThe attacker discovers that the authentication backend normalizes header names, treating \u003ccode\u003eX_Forwarded_Proto\u003c/code\u003e and \u003ccode\u003eX-Forwarded-Proto\u003c/code\u003e as equivalent.\u003c/li\u003e\n\u003cli\u003eThe attacker crafts an HTTP request with alias headers, such as \u003ccode\u003eX_Forwarded_Proto: https\u003c/code\u003e and \u003ccode\u003eX_Forwarded_Host: trusted.example\u003c/code\u003e.\u003c/li\u003e\n\u003cli\u003eTraefik receives the request and forwards it to the authentication backend without sanitizing the alias headers.\u003c/li\u003e\n\u003cli\u003eThe authentication backend processes the request and normalizes the header names.\u003c/li\u003e\n\u003cli\u003eThe authentication backend evaluates trust predicates based on the spoofed values in the alias headers.\u003c/li\u003e\n\u003cli\u003eThe authentication backend incorrectly determines that the request is authenticated based on the spoofed trust context.\u003c/li\u003e\n\u003cli\u003eTraefik grants the attacker access to the protected resource, bypassing authentication.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eThis vulnerability allows unauthenticated attackers to bypass authentication and access protected endpoints. In deployments where authorization decisions depend on forwarded headers, attackers can interact with backend services as if they were fully authenticated. This can expose sensitive internal functionality and data, potentially leading to data breaches or unauthorized access to critical systems. Successful exploitation undermines the security provided by \u003ccode\u003eForwardAuth\u003c/code\u003e and similar authentication mechanisms.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade Traefik to version 2.11.43, 3.6.14, or 3.7.0-rc.2 or later to address the vulnerability.\u003c/li\u003e\n\u003cli\u003eImplement a unified normalization policy across all forwarded header families, including RFC7239 and \u003ccode\u003eX-Forwarded-*\u003c/code\u003e to remediate the root cause.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule \u003ccode\u003eDetect Traefik ForwardAuth Bypass Attempt\u003c/code\u003e to identify exploitation attempts based on the presence of unusual \u003ccode\u003eX_Forwarded_*\u003c/code\u003e headers.\u003c/li\u003e\n\u003cli\u003eRestrict the headers forwarded to authentication services using an explicit allowlist to minimize the attack surface.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-08-06T21:30:01Z","date_published":"2026-04-25T12:00:00Z","id":"https://feed.craftedsignal.io/briefs/2026-04-traefik-auth-bypass/","summary":"Traefik's `ForwardAuth` and snippet-based authentication middleware has a high severity authentication bypass vulnerability because it does not sanitize header aliases with underscores, allowing attackers to spoof trust context and bypass authentication on protected routes.","title":"Traefik ForwardAuth Authentication Bypass via Header Spoofing","url":"https://feed.craftedsignal.io/briefs/2026-04-traefik-auth-bypass/"}],"language":"en","title":"CraftedSignal Threat Feed - Cpe:2.3:a:traefik:traefik:3.7.0:ea2:*:*:*:*:*:*","version":"https://jsonfeed.org/version/1.1"}