Vulnerability · Published Feb 24, 2026 · Assigned by GitHub_M
CVE-2026-27588Caddy: MatchHost becomes case-sensitive for large host lists (>100), enabling host-based route/auth bypass
High 7.7
In plain English
A high-severity security flaw in caddy from caddyserver. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 37% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.23 | caddy | 2.11.2-r0 | ALPINE-CVE-2026-27588 |
| Alpine:v3.24 | caddy | 2.11.1-r0 | ALPINE-CVE-2026-27588 |
| Debian:12 | caddy | 2.6.2-5+deb12u1 | DEBIAN-CVE-2026-27588 |
| Debian:13 | caddy | 2.6.2-12+deb13u1 | DEBIAN-CVE-2026-27588 |
| Debian:14 | caddy | 2.11.2-1 | DEBIAN-CVE-2026-27588 |
| Go | github.com/caddyserver/caddy/v2 | 2.11.1 | GHSA-x76f-jf84-rqj8 |
| Go | github.com/caddyserver/caddy/v2 | 2.11.1 | GO-2026-4541 |
| Ubuntu:25.10 | caddy | no fix listed | UBUNTU-CVE-2026-27588 |
| Ubuntu:26.10 | caddy | no fix listed | UBUNTU-CVE-2026-27588 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| caddyserver | caddy | < 2.11.1 |
Weakness: CWE-178 · Vector: 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
References
- https://github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8 x_refsource_CONFIRM
- https://github.com/caddyserver/caddy/releases/tag/v2.11.1 x_refsource_MISC