Missing Authentication for Critical Function Affecting github.com/traefik/traefik/v2/pkg/middlewares/forwardedheaders package, versions <2.11.43
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Start learning- Snyk IDSNYK-GOLANG-GITHUBCOMTRAEFIKTRAEFIKV2PKGMIDDLEWARESFORWARDEDHEADERS-16301566
- published27 Apr 2026
- disclosed24 Apr 2026
- creditfancymalware
Introduced: 24 Apr 2026
CVE-2026-39858 Â (opens in a new tab)How to fix?
Upgrade github.com/traefik/traefik/v2/pkg/middlewares/forwardedheaders to version 2.11.43 or higher.
Overview
Affected versions of this package are vulnerable to Missing Authentication for Critical Function in the ServeHTTP() function, which does not sufficiently sanitize X- alias headers. An attacker can gain unauthenticated access to protected endpoints by injecting spoofed trust context with headers using underscores, such as X_Forwarded_Proto in place of the canonical X-Forwarded-Proto, which are not removed before forwarding.