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CVE-2026-40912 — v3

CVE-2026-40912 is a CWE-706 vulnerability in github.com/traefik/traefik/v3. A fix is available for github.com/traefik/traefik/v3 — see the affected versions and patch details below.

Traefik: StripPrefixRegex auth bypass via Path/RawPath desync

Also known asGHSA-6jwx-7vp4-9847GO-2026-5180
Published
Apr 30, 2026
Updated
Aug 12, 2026
Affected
4 pkgs
Patched
3 / 4
Exploits
None indexed
Exploitation data as of Sep 18, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40912.

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs54th percentile — riskier than 54% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

4 pkgs affected
🐹github.com/traefik/traefik/v3🐹github.com/traefik/traefik/v3🐹github.com/traefik/traefik/v2🐹github.com/traefik/traefik

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's StripPrefixRegex middleware when used in combination with ForwardAuth, BasicAuth, or DigestAuth. The middleware matches the regex against the decoded URL path but uses the resulting byte length to slice the percent-encoded raw path. When a dot (or multiple dots) appears in the prefix portion of the URL, the raw path after stripping becomes a dot-segment (e.g. /./admin/secret). ForwardAuth receives this dot-segment path in X-Forwarded-Uri, which does not match the protected path patterns and therefore allows the request through. The backend then normalizes the dot-segment to the real path per RFC 3986 and serves the protected content An unauthenticated attacker can exploit this against any backend that performs dot-segment normalization. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

Affected Packages

4 total 3 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/traefik/traefik/v3≥ 3.7.0-ea.1&&< 3.7.0-rc.23.7.0-rc.2go get github.com/traefik/traefik/v3@v3.7.0-rc.2
🐹Gogithub.com/traefik/traefik/v3≥ 3.0.0-beta1&&< 3.6.143.6.14go get github.com/traefik/traefik/v3@v3.6.14
🐹Gogithub.com/traefik/traefik/v2all versions2.11.43go get github.com/traefik/traefik/v2@v2.11.43
🐹Gogithub.com/traefik/traefikall versionsNo fix

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/traefik/traefik/v3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/traefik/traefik/v3 to 3.7.0-rc.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40912 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-40912 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-40912. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant
ProductFixed inAdvisory
Red Hat OpenShift Dev Spaces 3.28devspaces/traefik-rhel9:1779786779RHSA-2026:21772

Frequently Asked Questions

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's StripPrefixRegex middleware when used in combination with ForwardAuth, BasicAuth, or DigestAuth. The middleware matches the regex against the decoded URL path but uses the resulting byte length to slice the percent-encoded raw path. When a dot (or multiple dots) appears in the prefix portion of the URL, the raw path after stripping becomes a dot-segment (e.g. /./admin/secret). ForwardAuth receives this dot-segment path
O3 Security · Impact-Aware SCA

Is CVE-2026-40912 in your dependencies?

O3 Security finds CVE-2026-40912 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works
CVE-2026-40912: v3 Auth Bypass | O3 Security