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High, CVSS 7.8

Traefik has an StripPrefixRegex Middleware Authorization Bypass via Path/RawPath Desync

CVE-2026-40912GHSA-6jwx-7vp4-9847

What to do

Partial vendor fix. Follow the primary source's mitigation guidance and check back for a fix.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • Go github.com/traefik/traefik/v3

    Affected
    >= 3.7.0-ea.1, < 3.7.0-rc.2>= 3.0.0-beta1, < 3.6.14
    Fixed in
    3.7.0-rc.2, 3.6.14

  • Go github.com/traefik/traefik/v2

    Affected
    < 2.11.43
    Fixed in
    2.11.43

  • Go github.com/traefik/traefik

    Affected
    <= 1.7.34
    Fixed in
    no fixed version recorded

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
7.8 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N · score source
EPSS
  • CVE-2026-40912: 0.77% estimated exploitation activity in the next 30 days; percentile 55.56 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary 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. Patches - https://github.com/traefik/traefik/releases/tag/v2.11.43 - https://github.com/traefik/traefik/releases/tag/v3.6.14 -…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-6jwx-7vp4-9847

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2026-40912

Advisory: Traefik has an StripPrefixRegex Middleware Authorization Bypass via Path/RawPath Desync
IDs: CVE-2026-40912, GHSA-6jwx-7vp4-9847
Record: https://patchnext.com/advisories/cve-2026-40912 (revision 1, source checked 26 Oct 2026, 15:27 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/traefik/traefik/v3 3.7.0-rc.2, 3.6.14; github.com/traefik/traefik/v2 2.11.43. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/traefik/traefik/v3: affected >= 3.7.0-ea.1, < 3.7.0-rc.2; >= 3.0.0-beta1, < 3.6.14; fixed in 3.7.0-rc.2, 3.6.14
- Go github.com/traefik/traefik/v2: affected < 2.11.43; fixed in 2.11.43
- Go github.com/traefik/traefik: affected <= 1.7.34

## Suggested inspection (read-only)
- Go github.com/traefik/traefik/v3: check the installed version with your package manager.
- Go github.com/traefik/traefik/v2: check the installed version with your package manager.
- Go github.com/traefik/traefik: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/traefik/traefik/v3, github.com/traefik/traefik/v2, github.com/traefik/traefik.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6jwx-7vp4-9847 (GitHub-reviewed advisory GHSA-6jwx-7vp4-9847 lists affected ranges: Go github.com/traefik/traefik/v3 >=3.7.0-ea.1 =3.0.0-beta1 =0 =0 <=1.7.34)

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