Winter: Local File Inclusion through =include directives in JavaScript asset compilation

Impact

Affected versions of Winter CMS allow authenticated backend users with the cms.manage_assets permission ("Manage website assets - images, JavaScript files, CSS files") to disclose arbitrary files readable by the PHP process by placing an =include / =require directive in a theme JavaScript asset.

Winter\Storm\Parse\Assetic\Filter\JavascriptImporter processes =include / =require directives found in comment blocks of JavaScript assets passed through System\Classes\CombineAssets. The directive target was resolved relative to the including file's own directory with realpath() and inlined into the combined output with no confinement check, so a directive such as =include ../../../.env escaped the theme's asset tree and inlined an arbitrary server-readable file. The only restriction was that the target had to have a file extension, since extension-less names had .js appended to them.

Because the combined output is served through the combine/{file} route, which performs no authentication or authorization checks, the disclosed contents then became readable by unauthenticated visitors at a stable URL as soon as the asset was referenced by any template.

The leaked content includes any file the web process can read, most importantly the application .env file (disclosing APP_KEY and database credentials). Text files were disclosed intact; binary content was mangled by the minification pipeline.

This is the JavaScript-importer counterpart of GHSA-58fp-mcx6-7qf9 (Local File Inclusion through LESS @import directives) and of CVE-2023-52085 / GHSA-2x7r-93ww-cxrq — the same vulnerability class reached through a different asset combiner filter.

To actively exploit this issue, an attacker would need an authenticated backend account with the cms.manage_assets permission. By default this permission is assigned to the built-in Developer role. The Winter CMS maintainers strongly recommend that the cms.manage_assets permission only be reserved to trusted administrators and developers in general, as it grants direct write access to files that are combined and served publicly.

Patches

JavascriptImporter in Winter Storm now applies two independent gates to every =include / =require target:

1. Only .js targets may be inlined. Any other extension is rejected before path resolution, which neutralises disclosure of non-JavaScript server files such as , , and . Extension-less includes are unaffected, as they are resolved to before this check, exactly as before.