CVE-2026-27586
Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed
- State
- Published
- Severity
- 8.8 High
- Published
- Feb 24, 2026
- Updated
- Feb 26, 2026
- Reserved
- Feb 20, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 8.8 High | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:P | GitHub_M |
Weaknesses
- CWE-755 Improper Handling of Exceptional Conditions
Affected Products
| Product | Versions |
|---|---|
caddycaddyserver |
|
References
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