CVE-2026-29054

Workarounds

No workaround available.

For more information

If there are any questions or comments about this advisory, please open an issue.

Traefik's XForwarded middleware (removeConnectionHeaders) tries to prevent clients from using the Connection header to strip trusted X-Forwarded-* headers, but the protection compares the Connection tokens case-sensitively while the deletion is case-insensitive.

As a result, a remote unauthenticated client can send a lowercase token like Connection: x-real-ip and still trigger deletion of traefik-managed X-Real-Ip (and similarly named headers in the managed list).

This can cause downstream routing, scheme, and header-based authn/authz decisions to be evaluated with missing trusted forwarding identity headers.

Severity

CRITICAL

Rationale: the PoC demonstrates an end-to-end access control bypass pattern when a downstream service uses proxy-provided identity headers (for example, X-Real-Ip) for IP allowlists or trust decisions. A remote unauthenticated client can strip the traefik-managed identity header via a lowercase Connection token, causing the downstream service to evaluate the request without the expected header signal.

Relevant Links

• Repository: https://github.com/traefik/traefik
• Pinned commit: a4a91344edcdd6276c1b766ca19ee3f0e346480f
• Callsite (pinned): https://github.com/traefik/traefik/blob/a4a91344edcdd6276c1b766ca19ee3f0e346480f/pkg/middlewares/forwardedheaders/forwarded_header.go#L225

Vulnerability Details

Root Cause

removeConnectionHeaders uses a case-sensitive membership check for protected header names when inspecting Connection tokens, but it deletes headers via net/http which treats header names case-insensitively. A lowercase token bypasses the protection check and still triggers deletion.

Attacker Control / Attack Path

Remote unauthenticated HTTP client (untrusted IP) sends Connection: x-real-ip, and Traefik deletes the generated X-Real-Ip header.

Proof of Concept

The attached poc.zip contains a deterministic, make-based integration PoC with a canonical run and a negative control.

Canonical (vulnerable):

unzip poc.zip -d poc
cd poc
make test

Output contains:

[CALLSITE_HIT]: pkg/middlewares/forwardedheaders/forwarded_header.go:225
[PROOF_MARKER]: downstream_admin_bypass=1 x_real_ip_present=0

Control (same env, no lowercase token):

unzip poc.zip -d poc
cd poc
make test

Output contains:

[CALLSITE_HIT]: pkg/middlewares/forwardedheaders/forwarded_header.go:225
[NC_MARKER]: downstream_admin_bypass=0 x_real_ip_present=1

Expected: Connection tokens are handled case-insensitively and protected identity headers (for example, X-Real-Ip and X-Forwarded-*) are not deleted due to client-supplied Connection options (regardless of token casing).

Actual: Lowercase Connection tokens bypass the protection check and still trigger deletion of traefik-managed identity headers (for example, X-Real-Ip).

Recommended Fix

• Case-fold (or otherwise canonicalize) Connection header tokens before comparing them against protected header names.
• Add a regression test covering lowercase tokens (for example, Connection: x-real-ip).

Fix accepted when: a request with Connection: x-real-ip does not cause deletion of traefik-managed X-Real-Ip, and a regression test covers this behavior.

There is a potential vulnerability in Traefik managing the Connection header with X-Forwarded headers.

When Traefik processes HTTP/1.1 requests, the protection put in place to prevent the removal of Traefik-managed X-Forwarded headers (such as X-Real-Ip, X-Forwarded-Host, X-Forwarded-Port, etc.) via the Connection header does not handle case sensitivity correctly. The Connection tokens are compared case-sensitively against the protected header names, but the actual header deletion operates case-insensitively. As a result, a remote unauthenticated client can use lowercase Connection tokens (e.g. Connection: x-real-ip) to bypass the protection and trigger the removal of Traefik-managed forwarded identity headers.

This is a bypass of the fix for CVE-2024-45410.

Depending on the deployment, the impact may be higher if downstream services rely on these headers (such as X-Real-Ip or X-Forwarded-*) for authentication, authorization, routing, or scheme decisions.

CVE-2026-29054 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.11.38, 3.6.9); upgrading removes the vulnerable code path.

Kodem intelligence

• https://github.com/traefik/traefik/releases/tag/v2.11.38
• https://github.com/traefik/traefik/releases/tag/v3.6.9

1. What is CVE-2026-29054? CVE-2026-29054 is a high-severity security vulnerability in github.com/traefik/traefik/v2 (go), affecting versions >= 2.11.9, <= 2.11.37. It is fixed in 2.11.38, 3.6.9.
2. How severe is CVE-2026-29054? CVE-2026-29054 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-29054?
   • github.com/traefik/traefik/v2 (go) (versions >= 2.11.9, <= 2.11.37)
   • github.com/traefik/traefik/v3 (go) (versions >= 3.1.3, <= 3.6.8)
4. Is there a fix for CVE-2026-29054? Yes. CVE-2026-29054 is fixed in 2.11.38, 3.6.9. Upgrade to this version or later.
5. Is CVE-2026-29054 exploitable, and should I be worried? Whether CVE-2026-29054 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-29054 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-29054?
   • Upgrade github.com/traefik/traefik/v2 to 2.11.38 or later
   • Upgrade github.com/traefik/traefik/v3 to 3.6.9 or later