CVE-2026-88879
8.2, highTraefik is an HTTP reverse proxy and load balancer
- CVSS
- 8.2, high high CVSS v3.1
- EPSS, next 30 days
- 0.3% higher than 20.6% of scored CVEs
- Exploitation
- No public evidence
- Published
- 10 Sept 2026a month ago
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.
Details
- Vendor
- Traefik
- Product
- traefik
- Weakness
- CWE-290 (opens in a new tab)
- Status
- Analyzed
- Updated
- 8 Oct 2026
- Assigner
- disclosure@vulncheck.com
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N
References 2
Patches and fixes 1
The kind is read from NVD's tags where present and from the shape of the URL otherwise, so treat it as a hint.
Other Traefik CVEs
Every Traefik CVE we holdSame vendor in what we hold, not a known link between the flaws.
- CVE-2026-88007 traefik Improper Authentication Vulnerability EPSS 0.6% 9.1, critical
- CVE-2026-88008 traefik HTTP Request Smuggling Vulnerability EPSS 0.5% 9.1, critical
- CVE-2026-88004 Traefik is an open source HTTP reverse proxy and load balancer EPSS 0.5% 7.4, high
- CVE-2026-88009 traefik HTTP Request Smuggling Vulnerability EPSS 0.4% 8.2, high
- CVE-2026-88011 Traefik is an open source HTTP reverse proxy and load balancer EPSS 0.4% 8.1, high
- CVE-2026-85594 traefik Authorization Bypass Through User-Controlled Key Vulnerability EPSS 0.5% 9.8, critical
- CVE-2026-85595 traefik Improper Authentication Vulnerability EPSS 0.7% 9.8, critical
- CVE-2026-85596 traefik Improper Authentication Vulnerability EPSS 0.4% 9.8, critical
Beyond this page
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Assembled from the NVD 2.0 API, the CISA Known Exploited Vulnerabilities Catalog and FIRST EPSS. Scores are as of our last collection on 17 Oct 2026, not the live upstream state.