Paper/Archive/CVE-2026-27586

CVE-2026-27586

caddyserver caddy — Caddy's mTLS client authentication silently fails open when CA certificate file is missing or malformed

EPSS 0.3%public exploit CVSS 9.1

critical.is priorityof 100

CVSS 9.1 (NVD)9.1 / 10 × 3027.3 Not in CISA KEV+300.0 EPSS percentile 22.1.221 × 204.4 Exploit: SSVC poc+1010.0 SSVC exploitation: poc+100.0

Description · from the CVE record

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.

Affected

ProductAffectedFixed inSource

caddy< 2.11.1–CNA

Scores by source

NVD9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

GitHub_M (CNA)8.8CVSS: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

CISA ADPSSVCExploitation: poc · Automatable: yes · Technical impact: partial

References

refgithub.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7 refgist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48 refgithub.com/caddyserver/caddy/releases/tag/v2.11.1