Vulnerability Description
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.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Caddyserver | Caddy | < 2.11.1 |
Related Weaknesses (CWE)
References
- https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48Exploit
- https://github.com/caddyserver/caddy/releases/tag/v2.11.1Release Notes
- https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7ExploitVendor Advisory
FAQ
What is CVE-2026-27586?
CVE-2026-27586 is a vulnerability with a CVSS score of 9.1 (CRITICAL). 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 sil...
How severe is CVE-2026-27586?
CVE-2026-27586 has been rated CRITICAL with a CVSS base score of 9.1/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-27586?
Check the references section above for vendor advisories and patch information. Affected products include: Caddyserver Caddy.