# CVE-2026-27590

## Summary

- **CVE ID:** CVE-2026-27590
- **Severity:** HIGH
- **CVSS Score:** 8.9 (CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:P)
- **CWE:** CWE-20, CWE-180
- **Published:** Feb 24, 2026
- **Last Modified:** Mar 12, 2026

## 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.

## Affected Products

- caddyserver — caddy (< 2.11.1)

## References

- [CNA](https://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g)
- [CNA](https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38)
- [CNA](https://github.com/caddyserver/caddy/releases/tag/v2.11.1)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.54%
- **EPSS Percentile:** 43.8

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._