CVE-2026-27586
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.
EPSS 0.13% · 31.7th percentile
Risk Scores
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| caddyserver | caddy | < 2.11.1, 0, < 2.11.1 |
| github.com | caddyserver/caddy/v2 | 0, 0 |
Timeline
- Feb 24, 2026 CVE Published
- Feb 24, 2026 PoC Published
- Feb 25, 2026 EPSS Score
- Feb 25, 2026 PoC Published
- Feb 25, 2026 CVE Updated
- Feb 25, 2026 PoC Published
- Feb 26, 2026 EPSS Score
- Feb 28, 2026 EPSS Score
- Mar 1, 2026 EPSS Score
- Mar 3, 2026 EPSS Score
- Mar 4, 2026 EPSS Score
- Mar 6, 2026 EPSS Score
References
- https://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7 url
- https://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48 url
- https://github.com/caddyserver/caddy/releases/tag/v2.11.1 url
- https://nvd.nist.gov/vuln/detail/CVE-2026-27586 advisory
- https://github.com/caddyserver/caddy/commit/d42d39b4bc237c628f9a95363b28044cb7a7fe72 url
- https://github.com/caddyserver/caddy package
- https://pkg.go.dev/vuln/GO-2026-4539 url