Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
Summary
Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
Original description
The description as published by the source.
Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, two swallowed errors in ClientAuthentication.provision() cause mTLS client certificate authentication to silently fail open when a CA certificate file is missing, unreadable, or malformed. The server starts without error but accepts any client certificate signed by any system-trusted CA, completely bypassing the intended private CA trust boundary. Any deployment using trusted_ca_cert_file or trusted_ca_certs_pem_files for mTLS will silently degrade to accepting any system-trusted client certificate if the CA file becomes unavailable. This can happen due to a typo in the path, file rotation, corruption, or permission changes. The server gives no indication that mTLS is misconfigured. Version 2.11.1 fixes the vulnerability.
Source: OSV.dev (Open Source Vulnerabilities) NVD GitHub Advisory OSV
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-27586 caddy
- Ubuntu UBUNTU-CVE-2026-27586 caddy
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- web gist.github.com
- web github.com