Vulnerability 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). Version 2.11.1 fixes the issue.
CVSS Score
CRITICAL
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Caddyserver | Caddy | < 2.11.1 |
Related Weaknesses (CWE)
References
- https://github.com/caddyserver/caddy/releases/tag/v2.11.1Release Notes
- https://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96gExploitVendor Advisory
- https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38Third Party Advisory
FAQ
What is CVE-2026-27590?
CVE-2026-27590 is a vulnerability with a CVSS score of 9.8 (CRITICAL). 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 the...
How severe is CVE-2026-27590?
CVE-2026-27590 has been rated CRITICAL with a CVSS base score of 9.8/10. This is considered a critical vulnerability requiring immediate attention.
Is there a patch for CVE-2026-27590?
Check the references section above for vendor advisories and patch information. Affected products include: Caddyserver Caddy.