CVE-2026-27590

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.

Affected products

Caddy

Caddyserver Caddy

< 2.11.1

Fix

Available

CVSS 3.1

9.8 CRITICAL

EPSS

0.5% (43th percentile)

Weakness

CWE-20, CWE-180

NVD status

Analyzed

Published

2026-02-24

No exploit for CVE-2026-27590 has been indexed yet. Our index is built from live traffic and upstream syncs, so this page can only say what it knows — not that no exploit exists.