CVE-2026-27588
An attacker can bypass host-based routing and any access controls attached to that route by changing the casing of the `Host` header.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.37%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
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.
- CVSS 4.0
- 7.7 HIGHCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M
- EPSS
- 0.37% probability · 30th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-178
- Affected
- caddyserver/caddy
- Source
- security-advisories@github.com
References
- https://github.com/caddyserver/caddy/releases/tag/v2.11.1Release Notes
- https://github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8Exploit, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.