CVE-2026-88011
published 2026-09-10CVE-2026-88011: Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as…
PriorityP352high8.1CVSS 3.1
AVNACLPRLUINSUCHIHAN
EPSS
0.42%
35.2th percentile
Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.
Affected
6 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| devspaces | traefik-rhel9 | — | — |
| github.com | traefik_traefik_v2 | >= 0 < 2.11.56 | 2.11.56 |
| github.com | traefik_traefik_v3 | >= 3.0.0 < 3.7.12 | 3.7.12 |
| traefik | traefik | < 2.11.56 | 2.11.56 |
| traefik | traefik | — | — |
| traefik | traefik | >= 3.0.0 < 3.7.12 | 3.7.12 |
CVSS provenance
nvdv3.18.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
nvdv4.05.3MEDIUMCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vendor_redhat8.1HIGH
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GHSA
Traefik: ForwardAuth identity spoofing via dot-form header alias
ghsa·2026-09-10
CVE-2026-88011 [MEDIUM] CWE-290 Traefik: ForwardAuth identity spoofing via dot-form header alias
Traefik: ForwardAuth identity spoofing via dot-form header alias
## Summary
There is a medium severity vulnerability in Traefik's handling of request headers whose name aliases another header name. Go canonicalizes header names on dashes only, so `X-Auth-User`, `X_Auth_User` and `X.Auth.User` are three distinct headers to Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX, and others) collapse all of them into the same variable. A client can therefore smuggle an alias of a header that Traefik manages past the middleware managing it — for example a dot-form `X.Authenticated.User` alongside the canonical `X-Authenticated-User` written by the ForwardAuth middleware — and have such a backend read the client-supplied value instead of the identity Traef
Red Hat
github.com/traefik/traefik: Traefik: Identity spoofing via dot-form header alias
vendor_redhat·2026-09-10·CVSS 8.1
CVE-2026-88011 [HIGH] CWE-444 github.com/traefik/traefik: Traefik: Identity spoofing via dot-form header alias
github.com/traefik/traefik: Traefik: Identity spoofing via dot-form header alias
Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.
A flaw was found in Traefik,
No detection rules found.
No public exploits indexed.
https://github.com/traefik/traefik/commit/0331801c72329e0eaeb850e53ccce87c57fbecf8https://github.com/traefik/traefik/pull/13720https://github.com/traefik/traefik/releases/tag/v2.11.56https://github.com/traefik/traefik/releases/tag/v3.7.12https://github.com/traefik/traefik/security/advisories/GHSA-rf44-j88r-hh8c
2026-09-10
Published