Craft CMS from 4.0.0-RC1 contains an authenticated path traversal vulnerability in the assets/icon endpoint where the extension parameter is not validated before file existence checks. Attackers can bypass extension validation by passing traversal sequences that resolve to existing SVG files, allowing local file read access.

Affected: Packagist: craftcms/cms

### Summary

An authenticated path traversal in `assets/icon` allows local SVG file read by passing traversal sequences in the `extension` parameter. The issue is caused by file existence checks happening before extension validation.

### Details The endpoint: - `src/controllers/AssetsController.php:1115-1123` - `actionIcon(string $extension)` calls `Assets::iconPath($extension)` and returns `sendFile($path, ...)`.

In `Assets::iconPath()`: - Path is built from user-controlled `extension`: - `src/helpers/Assets.php:906-909` - If `file_exists($path)` is true, path is returned immediately: - `src/helpers/Assets.php:910-912`

Validation exists in `Assets::iconSvg()`: - `preg_match('/^\w+$/', $extension)` - `src/helpers/Assets.php:927-931`

However, that validation is only reached if `iconPath()` does **not** find a file. So traversal payloads that resolve to existing `.svg` files bypass validation and are served by `sendFile()`.

### Impact

- Authenticated users can read local .svg files accessible to the application process.

### References

- https://github.com/craftcms/cms/commit/30f5f1a8d6edf0f3a00be72c42c78d9dc7d72d5c