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Fencer Intel
high 8.6

CVE-2026-40912 json

Traefik: StripPrefixRegex auth bypass via Path/RawPath desync

published 6mo ago modified 3mo ago also EUVD-2026-26428 , GHSA-6jwx-7vp4-9847 , GO-2026-5180

cvss
8.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 55%
public exploits
0
none known

Summary

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.

Patch / fix

  • go github.com/traefik/traefik/v3 3.6.14, 3.7.0-rc.2
  • go github.com/traefik/traefik/v2 2.11.43
  • Red Hat Red Hat OpenShift Dev Spaces 3.28 1779786779
  • govulncheck-vulndb openSUSE Leap 16.0 0.0.20260723T184607-160000.1.1
  • traefik openSUSE Tumbleweed 3.6.15-1.1
  • traefik2 openSUSE Tumbleweed 2.11.44-1.1

opensuse advisories openSUSE-SU-2026:21483-1openSUSE-SU-2026:10697-1openSUSE-SU-2026:10698-1

Is CVE-2026-40912 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-40912 updated cvss 8.6

github.com/traefik/traefik: Traefik: Authentication bypass via crafted URL dot-segments in StripPrefixRegex middleware

  • Red Hat OpenShift Dev Spaces 3.28 devspaces/traefik-rhel9 1779786779
    fixed: vendor fix RHSA-2026:21772
  • Red Hat OpenShift Dev Spaces 3.28 devspaces/udi-rhel9 1779829736, devspaces/code-rhel9 1779814592, devspaces/server-rhel9 1779342423, devspaces/openvsx-rhel9 1779528224, devspaces/udi-base-rhel9 1779741066, devspaces/code-sshd-rhel9 1779813519, +9 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
6mo ago

Exploit prediction

0.77% chance of exploitation in the next 30 days, higher than 55% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/traefik/traefik/security/advisories/GHSA-6jwx-7vp4-9847 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 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
CISA ADP 3.1 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
GitHub 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
CNA 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 8.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
CNA 3.1 8.6 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Affected packages

ecosystem package affected fixed in
go github.com/traefik/traefik/v3
>=3.7.0-ea.1, <3.7.0-rc.2
>=3.0.0-beta1, <3.6.14
3.7.0-rc.2
3.6.14
go github.com/traefik/traefik/v2
<2.11.43
2.11.43
go github.com/traefik/traefik
<=1.7.34
all versions
 no fix listed

Affected products

  • traefik traefik
  • Red Hat Red Hat OpenShift Dev Spaces 3.28

Classification

Weakness
  • CWE-706 Use of Incorrectly-Resolved Name or Reference
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.