October CMS has Safe Mode Bypass via CSS Preprocessor Compilers

A server-side information disclosure vulnerability was identified in the handling of CSS preprocessor files. Backend users with Editor permissions could craft .less, .sass, or .scss files that leverage the compiler's import functionality to read arbitrary files from the server. This worked even with cms.safe_mode enabled.

Impact

• Potential exposure of sensitive server-side files
• Requires authenticated backend access with Editor permissions
• Only relevant when cms.safe_mode is enabled (otherwise direct PHP injection is already possible)

Patches

The vulnerability has been patched in v3.7.14 and v4.1.10. When cms.safe_mode is enabled, .less, .sass, and .scss files can no longer be created, uploaded, or edited across the CMS editor, media manager, and file upload interfaces. All users are encouraged to upgrade to the latest patched version.

Workarounds

If upgrading immediately is not possible:

• Set cms.editable_asset_types config to ['css', 'js'] to remove preprocessor file types from the editor

• Restrict Editor tool access to fully trusted administrators only

• Reported by Chris Alupului