GHSA-hcj7-6gxh-24ww

### Impact

A stored cross-site scripting (XSS) vulnerability allows any authenticated user to upload an SVG file containing JavaScript. The file is served inline with `Content-Type: image/svg+xml` and without protective headers, causing the browser to execute embedded scripts in the Parse Server origin. This can be exploited to steal session tokens from `localStorage` and achieve account takeover.

The default `fileExtensions` option blocks HTML file extensions but does not block SVG, which is a well-known XSS vector. All Parse Server deployments where file upload is enabled for authenticated users (the default) are affected.

### Patches

The fix adds `svg` (case-insensitive) to the default file extension denylist. The default regex changes from `^(?![xXsS]?[hH][tT][mM][lL]?$)` to `^(?!([xXsS]?[hH][tT][mM][lL]?|[sS][vV][gG])$)`.

### Workarounds

Configure the `fileExtensions` option to explicitly block SVG uploads:

```js { fileUpload: { fileExtensions: ['^(?!([xXsS]?[hH][tT][mM][lL]?|[sS][vV][gG])$)'] } } ```

### References

- GitHub security advisory: https://github.com/parse-community/parse-server/security/advisories/GHSA-hcj7-6gxh-24ww - Fix Parse Server 9: https://github.com/parse-community/parse-server/releases/tag/9.5.2-alpha.4 - Fix Parse Server 8: https://github.com/parse-community/parse-server/releases/tag/8.6.17