Is CVE-2026-88011 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-88011 being exploited in the wild.

How severe is CVE-2026-88011?

High severity, with a CVSS score of 8.1, published 10 September 2026.

Which products and versions are affected?

github.com/traefik/traefik (Go) SEMVER:introduced=0; github.com/traefik/traefik/v2 (Go) = 3.0.0, < 3.7.12, SEMVER:introduced=3.0.0,fixed=3.7.12; Traefik 1.x, 2.0 through 2.11.55, 3.0.0 through 3.7.11.

Is there a fix for CVE-2026-88011?

Yes. github.com/traefik/traefik/v2 (Go): upgrade to 2.11.56 or later; github.com/traefik/traefik/v3 (Go): upgrade to 3.7.12 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-88011 attacked?

It is attacked over the network.

Am I affected by CVE-2026-88011?

Check whether you run github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-88011: Traefik ForwardAuth identity spoofing via header alias

Q: Is there a fix for CVE-2026-88011?

Yes. github.com/traefik/traefik/v2 (Go): upgrade to 2.11.56 or later; github.com/traefik/traefik/v3 (Go): upgrade to 3.7.12 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

Q: How is CVE-2026-88011 attacked?

It is attacked over the network.

Q: Am I affected by CVE-2026-88011?

Check whether you run github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-88011 · Severity: high · CVSS 8.1 · Published 2026-09-10

Traefik is a reverse proxy and load balancer used to route incoming traffic to backend applications. The ForwardAuth middleware, which enforces authentication by delegating identity verification to an external service, can be bypassed by sending request headers with alternative name formats (e.g., using dots instead of dashes). An authenticated attacker with lower privileges can craft a request that causes the backend server to treat them as a different user or administrator, potentially gaining unauthorized access to sensitive functionality or data.

Technologies: github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go), Traefik. Vendors: Go, Traefik.

Quick answers

Is CVE-2026-88011 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-88011 being exploited in the wild.
How severe is CVE-2026-88011?: High severity, with a CVSS score of 8.1, published 10 September 2026.
Which products and versions are affected?: github.com/traefik/traefik (Go) SEMVER:introduced=0; github.com/traefik/traefik/v2 (Go) < 2.11.56, SEMVER:introduced=0,fixed=2.11.56; github.com/traefik/traefik/v3 (Go) >= 3.0.0, < 3.7.12, SEMVER:introduced=3.0.0,fixed=3.7.12; Traefik 1.x, 2.0 through 2.11.55, 3.0.0 through 3.7.11.
Is there a fix for CVE-2026-88011?: Yes. github.com/traefik/traefik/v2 (Go): upgrade to 2.11.56 or later; github.com/traefik/traefik/v3 (Go): upgrade to 3.7.12 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-88011 attacked?: It is attacked over the network.
Am I affected by CVE-2026-88011?: Check whether you run github.com/traefik/traefik (Go), github.com/traefik/traefik/v2 (Go), github.com/traefik/traefik/v3 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

github.com/traefik/traefik/v2 (Go): upgrade to 2.11.56 or later
```
go get github.com/traefik/traefik/v2@v2.11.56
```
github.com/traefik/traefik/v3 (Go): upgrade to 3.7.12 or later
```
go get github.com/traefik/traefik/v3@v3.7.12
```

Technical details

This is a header canonicalization bypass vulnerability affecting Traefik's ForwardAuth middleware. Go's HTTP implementation canonicalizes header names only on dashes, treating X-Authenticated-User, X_Authenticated_User, and X.Authenticated.User as three distinct header names. However, backend servers (PHP, NGINX, CGI, WSGI) normalize all forms to a single environment variable (e.g., HTTP_X_AUTHENTICATED_USER). The ForwardAuth middleware deletes and replaces only the canonical dash-form header after authentication, allowing an attacker to inject a dot-form alias that survives this filtering. When the reverse proxy forwards both headers to the backend, PHP and similar servers collapse them into one variable, with the attacker-controlled value taking precedence due to lexical header ordering. An attacker already permitted by ForwardAuth as a lower-privilege user can spoof a higher-privilege identity. The vulnerability was incomplete-fixed in a prior iteration (GHSA-x677-9fxg-v5c5) that only blocked underscore forms. Patches are available in Traefik v2.11.56 and v3.7.12, introducing an aliasHeadersStrategy option (defaulting to 'keep') that must be explicitly set to 'delete' or 'reject' to mitigate the issue.

Affected products

Traefik Traefik 1.x, 2.0 through 2.11.55, 3.0.0 through 3.7.11

Identifiers

CVE-2026-88011
GHSA-rf44-j88r-hh8c
GO-2026-6455

Timeline

2026-09-10: disclosed
2026-09-10: patched: Patches released: v2.11.56 and v3.7.12

References

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