Winter CMS is a content management system built on the Laravel PHP framework. In versions up to and including 1.2.12, authenticated backend users can disclose arbitrary files readable by the PHP process by injecting @import (inline) directives into LESS source that the backend compiles, because the LESS parser was instantiated without a safe import resolver and fell back to the raw attacker-supplied path when no allowed root matched. The flaw is reachable through four entry points that share the same root cause: the Brand Settings custom_css field, the Editor Settings html_custom_styles field, the Mail Brand Settings colour-picker fields whose values are concatenated into LESS source without escaping, and theme .less, .sass, and .scss assets compiled when served. Both absolute paths and .. traversal outside the asset's own tree were accepted, so an attacker could read any file the web process can access, most significantly the application .env file and the APP_KEY and database credentials it contains. Exploitation requires a backend account holding one of the associated permissions, which are assigned by default to the built-in Developer role. This issue is fixed in version 1.2.13.

Affected: Packagist: winter/wn-backend-module

### Impact

Affected versions of Winter CMS allow authenticated backend users with the following permissions to disclose arbitrary files readable by the PHP process by injecting `@import (inline) "<path>"` directives into LESS source that the backend compiles. Four entry points share the same root cause:

- **Brand Settings** `BrandSetting.custom_css` field (`backend.manage_branding`) — compiled inline into every backend page's `<style>` block. - **Editor Settings** `EditorSetting.html_custom_styles` field (`backend.manage_editor`) — compiled inline into every backend page's `<style>` block. - **Mail Brand Settings** `MailBrandSetting` colour-picker fields (`system.manage_mail_templates`) — values are concatenated into LESS source via `Less_Parser::ModifyVars()` with no escaping, so any value the form validator does not reject can carry an `@import` directive. - **Theme `.less`/`.sass`/`.scss` assets** (`cms.manage_assets`) — compiled through `System\Classes\CombineAssets` when served, with the same `Less_Parser` configuration. Both absolute paths and `..` traversal escape from the asset's own tree were exploitable.

The leaked content includes any file the web process can read, most importantly the application `.env` file (disclosing `APP_KEY` and database credentials).

To actively exploit this issue, an attacker would need an authenticated backend account with one of the permissions listed above. By default these are assigned to the built-in Developer role.

### Patches…