Craft CMS has authenticated path traversal in `assets/icon`, allowing local `.svg` file read

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