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CVE-2026-88879— Traefik before v2.11.56 Identity Spoofing via Header Alias

Quick assessment

Affected
traefik traefik
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

以下是该漏洞描述的中文翻译： Traefik 是一个 HTTP 反向代理和负载均衡器。在 Traefik v1.x、v2.x 至 v2.11.55 以及 v3.0.0 至 v3.7.11 版本中，头部（Header）名称仅在连字符（dash）上进行规范化。因此， 、 和 会被 Traefik 视为三个不同的头部。然而，那些从头部名称推导变量名的后端（如 CGI、WSGI、PHP、NGINX 等）会将这些变体合并为单个变量。 因此，客户端可以绕过管理特定头部的中间件，将头部名称的“点号”形式（dot-form ali

CVSS 5.3 · Medium
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I. Basic Information for CVE-2026-88879

Vulnerability Information
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Vulnerability Title
Traefik before v2.11.56 Identity Spoofing via Header Alias
Source: CVE Program / CVE List V5
Vulnerability Description
Traefik is an HTTP reverse proxy and load balancer. In Traefik v1.x, v2.x through v2.11.55, and v3.0.0 through v3.7.11, header names are canonicalized only on dashes, so X-Auth-User, X_Auth_User and X.Auth.User are treated as three distinct headers by Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX and others) collapse them into a single variable. A client can therefore smuggle a dot-form alias of a header that Traefik manages past the middleware managing it — for example supplying X.Authenticated.User alongside the canonical X-Authenticated-User written by the ForwardAuth middleware — causing such a backend to read the client-supplied value instead of the identity Traefik asserted. In the tested configuration (PHP 8.2 built-in SAPI over an HTTP/1 backend path), Go's lexical header ordering makes the attacker-supplied value win deterministically, so a client that ForwardAuth admits as a low-privilege identity can be treated by the backend as a different user or role. Any header Traefik sets is affected, not only ForwardAuth's. This is an incomplete fix for GHSA-x677-9fxg-v5c5, which blocked only the underscore form. Fixed in v2.11.56 and v3.7.12, which add the aliasHeadersStrategy entry-point option; because it defaults to 'keep' for backwards compatibility, it must be explicitly set to 'delete' or 'reject' for the fix to take effect. Unmaintained release lines will not receive a patch.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
Source: CVE Program / CVE List V5
Vulnerability Type
使用欺骗进行的认证绕过
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
traefik traefik 0 ~ 2.11.56 -
traefik traefik 3.0.0 ~ 3.7.13 -

II. Public POCs for CVE-2026-88879

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III. Intelligence Information for CVE-2026-88879

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Vendor Advisories for CVE-2026-88879 (2)

Same Patch Batch · traefik · 2026-09-10 · 9 CVEs total

CVE-2026-88877 9.8 CRITICAL Traefik v3.7.0 Authentication Bypass via from-to-www-redirect
CVE-2026-88007 9.1 CRITICAL Traefik HTTP/3 Backend NTLM Connection Reuse
CVE-2026-88009 8.8 HIGH Traefik: Rootless HTTP/1 request-target routes as "/" but is forwarded verbatim, bypassing
CVE-2026-88004 7.0 HIGH Traefik entrypoint header-name sanitization bypassed via request trailers
CVE-2026-88008 7.0 HIGH Traefik: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CVE-2026-88878 5.3 MEDIUM Traefik v2.8.2 through v3.6 HTTP/3 Timeout Bypass
CVE-2026-88011 5.3 MEDIUM Traefik: ForwardAuth identity spoofing via dot-form header alias
CVE-2026-88012 5.3 MEDIUM Traefik: respondingTimeouts.readTimeout is not applied to HTTP/3, leaving slow-body upload

IV. Related Vulnerabilities

Same product: traefik
Same vendor: traefik
Same weakness: CWE-290

V. Comments for CVE-2026-88879

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