CVE-2026-27590

9.8 CRITICAL
Published: February 24, 2026 Modified: February 25, 2026
View on NVD

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.

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CVSS v3.x Details

0.0 Low Medium High Critical 10.0
Vector String
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References to Advisories, Solutions, and Tools

Patch Vendor Advisory Exploit Third Party Advisory
https://github.com/caddyserver/caddy/releases/tag/v2.11.1
Source: security-advisories@github.com
Release Notes
https://github.com/caddyserver/caddy/security/advisories/GHSA-5r3v-vc8m-m96g
Source: security-advisories@github.com
Exploit Vendor Advisory
https://github.com/php/frankenphp/security/advisories/GHSA-g966-83w7-6w38
Source: security-advisories@github.com
Third Party Advisory

3 reference(s) from NVD

Quick Stats

CVSS v3 Score
9.8 / 10.0
EPSS (Exploit Probability)
0.2%
41th percentile
Exploitation Status
Not in CISA KEV

Weaknesses (CWE)

Affected Vendors

caddyserver