CVE-2026-63179

Winter: Local File Inclusion through @import directives in LESS compilation of backend customizable stylesheets and theme assets

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.

Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.

CVE-2026-63179 has a CVSS score of 4.9 (Medium). The vector is network-reachable, high privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.2.13); upgrading removes the vulnerable code path.

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The root cause is in the wikimedia/less.php integration in Winter Storm: Less_Parser was instantiated without a safe import resolver, and its Less_FileManager::getFilePath() falls back to the raw attacker-supplied path when no candidate root matches. Storm now ships a LessImportResolver that uses the callable form of Less_Parser::SetImportDirs() to refuse any @import whose resolved path lies outside the calling context's allowed roots, defeating both absolute paths and .. traversal at the parser level.

The four sinks have been updated to use the resolver. The three settings models pass no allowed roots (deny-all) because the bundled stylesheets ship no @import directives and the user fields have no legitimate use for them. System\Classes\CombineAssets configures the theme-asset compiler with themes_path(), plugins_path(), and base_path('modules') as allowed roots, preserving real cross-tree imports observed in shipped themes and plugins.

This security issue has been fixed in v1.2.13 (Winter core) and v1.2.13 (Winter Storm).

1. What is CVE-2026-63179? CVE-2026-63179 is a medium-severity path traversal vulnerability in winter/wn-backend-module (composer), affecting versions <= 1.2.12. It is fixed in 1.2.13. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
2. How severe is CVE-2026-63179? CVE-2026-63179 has a CVSS score of 4.9 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of winter/wn-backend-module are affected by CVE-2026-63179? winter/wn-backend-module (composer) versions <= 1.2.12 is affected.
4. Is there a fix for CVE-2026-63179? Yes. CVE-2026-63179 is fixed in 1.2.13. Upgrade to this version or later.
5. Is CVE-2026-63179 exploitable, and should I be worried? Whether CVE-2026-63179 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-63179 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-63179? Upgrade winter/wn-backend-module to 1.2.13 or later.