CVE-2026-27590

The record

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 packages

Related vulnerabilities

• GO-2026-4536 Unicode case-folding causes incorrect split_path index in github.com/caddyserver/caddy/v2 Same vulnerability
• GO-2026-4535 Improper sanitization of glob characters in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• GO-2026-4539 Caddy mTLS authentication fails open in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• GO-2026-4537 Caddy is vulnerable to cross-origin config application via local admin API /load in… Also affects github.com/caddyserver/caddy/v2
• GO-2026-4541 Caddy MatchHost becomes case-sensitive in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• GO-2026-4538 Caddy MatchPath %xx branch skips case normalization in github.com/caddyserver/caddy/v2 Also affects github.com/caddyserver/caddy/v2
• CVE-2026-27589 Caddy is an extensible server platform that uses TLS by default. Also affects github.com/caddyserver/caddy/v2
• CVE-2026-27588 Caddy is an extensible server platform that uses TLS by default. Also affects github.com/caddyserver/caddy/v2