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.

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-sens…

EPSS: 0.004 (29.4th percentile) — read the EPSS interpretation.

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.

Affected products

Caddyserver Caddy — versions < 2.11.1

Weakness classification (CWE)

CWE-178 — Improper Handling of Case Sensitivity

References

security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
security-advisories@github.com (x_refsource_MISC, 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.