CVE-2026-27588
CRITICAL9.1EPSS 0.06%Caddy MatchHost becomes case-sensitive in github.com/caddyserver/caddy/v2
Published: 2/24/2026Modified: 4/30/2026
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.
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:N/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 (7)
- ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-27588
- ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2026-27588
- PATCHhttps://github.com/caddyserver/caddy
- WEBhttps://github.com/caddyserver/caddy/commit/eec32a0bb5a11651c6a7b04ce82dc50610f2b27e
- WEBhttps://github.com/caddyserver/caddy/releases/tag/v2.11.1
- WEBhttps://github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8
- WEBhttps://pkg.go.dev/vuln/GO-2026-4541