FrankenPHP is a modern application server for PHP. From version 1.11.2 to before version 1.12.3, the splitPos() function in cgi.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 FrankenPHP into treating a non-.php file as a .php script. In any deployment where the attacker can place content into a file served by FrankenPHP (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw. This issue has been patched in version 1.12.3.

Affected: Go: github.com/dunglas/frankenphp

### Summary

The `splitPos()` function in [`cgi.go`](https://github.com/php/frankenphp/blob/main/cgi.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 FrankenPHP into treating a non-`.php` file as a `.php` script. In any deployment where the attacker can place content into a file served by FrankenPHP (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw.

This advisory consolidates two independent reports against the same function (the duplicate, GHSA-v4h7-cj44-8fc8, has been closed). Both were reported by @KC1zs4.

### Details

```go var splitSearchNonASCII = search.New(language.Und, search.IgnoreCase)

func splitPos(path string, splitPath []string) int { if len(splitPath) == 0 { return 0 } pathLen := len(path) for _, split := range splitPath { splitLen := len(split) for i := 0; i < pathLen; i++ { if path[i] >= utf8.RuneSelf { if _, end := splitSearchNonASCII.IndexString(path, split); end > -1 { return end } break } if i+splitLen > pathLen { continue } match := true for j := 0; j < splitLen; j++ { c := path[i+j] if c >= utf8.RuneSelf { if _, end := splitSearchNonASCII.IndexString(path, split); end > -1 { return end } break // <-- flaw 1: 'match' is still true } if 'A' <= c && c <= 'Z' { c +=…