GHSA-hmr5-2xcr-v8pp

### Description

Symfony's profiler, a development only debug UI, renders source-code excerpts on several pages using Twig's custom `file_excerpt` filter. This filter renders PHP files via `highlight_string()` (which escapes HTML), but renders **non-PHP files** by splitting on `\n` and interpolating each line directly into `<code>{$line}</code>` with no escaping.

An attacker who can write arbitrary bytes into any file under the project root (including e.g. `var/log/dev.log`), achieves **stored XSS** against any developer who later opens that file in the profiler.

### Resolution

The `file_excerpt` filter now properly escapes each line of non-PHP files using `htmlspecialchars()` before concatenating them.

The patch for this issue is available [here](https://github.com/symfony/symfony/commit/863aa81c61166f1aa74b7732df316f76113acbdb) for branch 6.4.

### Credits

Symfony would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix.