CVE-2026-40912 Details
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.
A high-severity authentication bypass vulnerability exists in Traefik's StripPrefixRegex middleware, specifically in versions through 2.11.42, 3.6.13, and 3.7.0-rc.1. The vulnerability arises when the middleware is used with ForwardAuth, BasicAuth, or DigestAuth. The issue occurs because the middleware matches regex against the decoded URL path but slices the percent-encoded raw path using the resulting byte length. This discrepancy can create a dot-segment path (e.g., /./admin/secret) when dots are present in the URL prefix. ForwardAuth then receives this dot-segment path in the X-Forwarded-Uri header, which bypasses the protected path patterns, allowing the request to be processed by the backend. The backend normalizes the dot-segment to the actual path according to RFC 3986 and serves the protected content. This vulnerability can be exploited by an unauthenticated attacker against any backend that normalizes dot-segments.
Users can upgrade to Traefik versions 2.11.43, 3.6.14, or 3.7.0-rc.2 to address this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 1, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://access.redhat.com/errata/RHSA-2026:21772 | redhat-SADP | |
| https://access.redhat.com/security/cve/CVE-2026-40912 | redhat-SADP | |
| https://bugzilla.redhat.com/show_bug.cgi?id=2464229 | redhat-SADP | |
| https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40912.json | redhat-SADP | |
| https://github.com/traefik/traefik/releases/tag/v2.11.43 | [email protected] | ProductRelease Notes |
| https://github.com/traefik/traefik/releases/tag/v3.6.14 | [email protected] | ProductRelease Notes |
| https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2 | [email protected] | ProductRelease Notes |
| https://github.com/traefik/traefik/security/advisories/GHSA-6jwx-7vp4-9847 | [email protected] | ExploitPatchVendor Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-22 | Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') | redhat-SADP |
| CWE-706 | Use of Incorrectly-Resolved Name or Reference | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| traefik traefik | < 2.11.43 >= 3.0.0, < 3.6.14 3.7.0 ea1 3.7.0 ea2 3.7.0 ea3 3.7.0 rc1 |
CPE
Remediation
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Change History
6 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jul 15, 2026 | CVE Modified | redhat-SADP |
| Jun 30, 2026 | CVE Modified | redhat-SADP |
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 1, 2026 | Initial Analysis | [email protected] |
| Apr 30, 2026 | New CVE Received | [email protected] |