CVE-2026-65600
Summary
There is a critical authentication-bypass vulnerability in Traefik's ReplacePathRegex middleware. When it is configured with a regular expression that captures user-controlled path segments without a mandatory separator (for example regex: "^/api(.*)", replacement: "/$1"), a crafted request can produce an un-normalized replacement path such as /../admin, which Traefik forwarded to the backend without validation. A backend that normalizes the path may resolve it to a protected route, letting an unauthenticated attacker reach resources located behind authentication middleware. This is the same class of issue that was fixed for StripPrefix in CVE-2026-48020; that post-replacement normalization check had not been applied to ReplacePathRegex. The fix rejects any request whose replaced path does not match its normalized form.
Patches
- https://github.com/traefik/traefik/releases/tag/v2.11.52
- https://github.com/traefik/traefik/releases/tag/v3.6.23
- https://github.com/traefik/traefik/releases/tag/v3.7.7
For more information
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<details>
<summary>Original Description</summary>
Summary
A path traversal vulnerability in the ReplacePathRegex middleware allows an unauthenticated remote attacker to bypass authentication middleware and access protected routes by sending a single crafted HTTP request. The vulnerability exists because ReplacePathRegex does not perform post-replacement path normalization validation - the same check added to StripPrefix in the fix for CVE-2026-48020 was not applied to ReplacePathRegex.
Details
When ReplacePathRegex is configured with a regex that captures user-controlled path segments without a mandatory path separator (e.g., regex: "^/api(.*)", replacement: "/$1"), an attacker can inject implicit traversal sequences into the capture group.
Root cause: pkg/middlewares/replacepathregex/replace_path_regex.go, function ServeHTTP (lines 56-74). After the rege
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Exploitation outlook
- Low exploitation risk0.41% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 34% of all EPSS-scored CVEs.
Advisory coverage (2)
External references
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