Vulnerability in Caddyserver Caddy
CVE-2026-27588
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 9.1 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.
EPSS exploit prediction
EPSS: 0.006 (45.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002
Affected products
- Caddyserver Caddy — versions < 2.11.1
Weakness classification (CWE)
References
- github.com/caddyserver/caddy/security/advisories/GHSA-x76f-jf84-rqj8 (Exploit, Vendor Advisory)
- github.com/caddyserver/caddy/releases/tag/v2.11.1 (Release Notes)
Frequently asked questions
- What is CVE-2026-27588?
- CVE-2026-27588 is a critical-severity vulnerability in Caddyserver Caddy, classified under Improper Handling of Case Sensitivity. CVSS score: 9.1/10. Published 2026-02-24.
- How severe is CVE-2026-27588?
- Critical severity. CVSS v3 base score is 9.1 out of 10.