{"schemaVersion":3,"id":"CVE-2026-27590","aliases":["UBUNTU-CVE-2026-27590","DEBIAN-CVE-2026-27590","GHSA-5r3v-vc8m-m96g","GO-2026-4536"],"status":"published","duplicateOf":null,"title":null,"description":"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). 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