CVE-2026-27590

moderate-risk

Published 2026-02-24

Caddy is an extensible server platform that uses TLS by default. Prior to version 2.11.1, Caddy's FastCGI path splitting logic computes the split index on a lowercased copy of the request path and then uses that byte index to slice the original path. This is unsafe for Unicode because `strings.ToLower()` can change UTF-8 byte length for some characters. As a result, Caddy can derive an incorrect `SCRIPT_NAME`/`SCRIPT_FILENAME` and `PATH_INFO`, potentially causing a request that contains `.php` to execute a different on-disk file than intended (path confusion). In setups where an attacker can control file contents (e.g., upload features), this can lead to unintended PHP execution of non-.php files (potential RCE depending on deployment). Version 2.11.1 fixes the issue.

Do I need to act?

0.29% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 9.8/10 Critical

NETWORK / LOW complexity

Affected Products (1)

Caddy

Affected Vendors

Caddyserver

References (3)

Release Notes https://github.com/caddyserver/caddy/releases/tag/v2.11.1

Exploit https://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g

Third Party Advisory https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38

/ 100

moderate-risk

Severity 32/34 · Critical

Exploitability 1/34 · Minimal

Exposure 5/34 · Minimal