CVE-2026-27588: Caddyserver Caddy

Critical severity, CVSS 9.1. EPSS: 0.5% chance of exploitation in the next 30 days.

Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's HTTP `host` request matcher is documented as case-insensitive, but when configured with a large host list (>100 entries) it becomes case-sensitive due to an optimized matching path. An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header. Version 2.11.1 contains a fix for the issue.

Affected products

• Caddyserver Caddy: from 2.10.2, before 2.11.1 (fixed in 2.11.1)

Published 2026-02-24. Last modified 2026-06-17.