CVE-2026-45135: caddyserver caddy Improper Input Validation

Vulnerability summary

CVE-2026-45135 is a high (CVSS 8.1) Improper Input Validation vulnerability in caddyserver caddy. EPSS estimates a 0.68% chance of exploitation in the next 30 days, higher than 51.3% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 23-06-2026
   PublishedVulnerability first disclosed.
2. 23-06-2026
   Last modifiedVulnerability information updated.

Description

Caddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport's splitPos() in modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go misuses golang.org/x/text/search with search.IgnoreCase when the request path contains a non-ASCII byte. Two distinct flaws in that fallback let an attacker mislead Caddy's FastCGI splitting into treating a non-.php (or other configured split_path extension) file as a script. In any deployment where the attacker can place content into a file served via FastCGI (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw. This vulnerability is fixed in 2.11.3.

• CWE-20Improper Input ValidationThe product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
• CWE-176Improper Handling of Unicode EncodingThe product does not properly handle when an input contains Unicode encoding.
• CWE-178Improper Handling of Case SensitivityThe product does not properly account for differences in case sensitivity when accessing or determining the properties of a resource, leading to inconsistent results.