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CVE-2026-85595 – Authentication Bypass (RCE-level dashboard/API exposure) – Traefik <2.11.55 and 3.0

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Summary

CVE-2026-85595 is a critical authentication bypass vulnerability in Traefik’s digestAuth middleware. When a client authenticates with an unknown username, the middleware’s secret provider returns an empty string instead of rejecting the request, and the digest library treats that empty string as a valid password hash (HA1). This allows any unauthenticated remote attacker to compute a valid digest response and gain access to routes, dashboards, or APIs protected by digestAuth, with a severity of 9.3 (Critical).

Technical details

  • Root cause: the digestAuth secret provider returns an empty string for usernames not present in the configured user list, rather than signaling "no such user."
  • The pinned digest authentication library accepts this empty string as the user’s HA1 hash instead of rejecting the lookup.
  • All other inputs to the digest computation are either chosen by the attacker or supplied to them in the server’s 401 challenge, so the expected response digest is fully computable offline.
  • Attack vector: network, no authentication or user interaction required, low attack complexity.
  • Impact: complete bypass of digestAuth-protected routes using an arbitrary username and no valid password, potentially exposing the Traefik dashboard, API, or any backend routed behind this middleware.

Affected software

  • Traefik (Go module) v2.x: all versions ≤ v2.11.54
  • Traefik (Go module) v3.x: versions v3.0.0 through v3.7.10

Severity

  • CVSS v4.0 Base Score: 9.3 (Critical)
  • Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade to Traefik v2.11.55 (2.x branch) or v3.7.11 (3.x branch) or later, which reject unknown usernames instead of returning an empty secret.
  • If no patch can be applied immediately: no official workaround is documented; as a network mitigation, restrict or remove reliance on digestAuth for protecting sensitive routes (dashboard, API) until the upgrade is complete, and consider placing an additional authentication layer or network-level access control (e.g., IP allowlisting) in front of affected endpoints.
  • Note: unmaintained v1 releases and older v2/v3 minor branches below the patched versions will not receive further updates; upgrade to a maintained release line.

How IONIX identifies potentially affected assets

IONIX matches the following signals against data already collected when it crawled the asset; identifying the technology sends no request beyond that crawl.

  • Page title: Traefik, Traefik Proxy
  • Response header content-security-policy: frame-src 'self' https://traefik.io https://*.traefik.io;

References

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