CVE-2026-27586
CRITICAL9.1EPSS 0.13%Caddy mTLS authentication fails open in github.com/caddyserver/caddy/v2
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.
Affected packages (3)
- Debian/caddyfrom 0
- Go/github.com/caddyserver/caddy/v2from 0, < 2.11.1
- Go/github.com/caddyserver/caddy/v2from 0, < 2.11.1
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | 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 |
| osv | CVSS 3.1 | CRITICAL9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
References (8)
- ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-27586
- ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2026-27586
- PATCHhttps://github.com/caddyserver/caddy
- WEBhttps://gist.github.com/moscowchill/9566c79c76c0b64c57f8bd0716f97c48
- WEBhttps://github.com/caddyserver/caddy/commit/d42d39b4bc237c628f9a95363b28044cb7a7fe72
- WEBhttps://github.com/caddyserver/caddy/releases/tag/v2.11.1
- WEBhttps://github.com/caddyserver/caddy/security/advisories/GHSA-hffm-g8v7-wrv7
- WEBhttps://pkg.go.dev/vuln/GO-2026-4539