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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.

Traefik是Traefik公司开源的一款负载均衡器。 Traefik 2.11.56之前版本和3.0.0版本至3.7.13版本存在授权问题漏洞，该漏洞源于仅对连字符形式的标头名称进行规范化，导致X-Auth-User、X_Auth_User和X.Auth.User被识别为不同标头，而后端（如CGI、WSGI、PHP、NGINX等）会将其合并为同一变量，攻击者可利用点号形式的标头别名绕过中间件管理，使后端读取客户端提供的值而非Traefik断言的身份，可能导致低权限身份被后端识别为其他用户或角色。

CVSS 5.3 · Medium EPSS 0.29% · P22

Affected Version Matrix 3

VendorProduct Version RangeStatus
traefik traefik < 2.11.56 affected
2.11.56 unaffected
3.0.0≤ 3.7.13 affected
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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
Vulnerability Title
Traefik 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Traefik是Traefik公司开源的一款负载均衡器。 Traefik 2.11.56之前版本和3.0.0版本至3.7.13版本存在授权问题漏洞，该漏洞源于仅对连字符形式的标头名称进行规范化，导致X-Auth-User、X_Auth_User和X.Auth.User被识别为不同标头，而后端（如CGI、WSGI、PHP、NGINX等）会将其合并为同一变量，攻击者可利用点号形式的标头别名绕过中间件管理，使后端读取客户端提供的值而非Traefik断言的身份，可能导致低权限身份被后端识别为其他用户或角色。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

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