How severe is GHSA-58fp-mcx6-7qf9?

GHSA-58fp-mcx6-7qf9 has a CVSS score of 4.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by GHSA-58fp-mcx6-7qf9?

GHSA-58fp-mcx6-7qf9 affects the following packages: winter/wn-backend-module (Packagist). Ecosystems affected: Packagist.

How do I fix GHSA-58fp-mcx6-7qf9?

Update winter/wn-backend-module to 1.2.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-58fp-mcx6-7qf9 is resolved across your whole dependency graph.

How do I detect GHSA-58fp-mcx6-7qf9 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for winter/wn-backend-module, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-58fp-mcx6-7qf9 if there is no patch (or I can't update yet)?

Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Is GHSA-58fp-mcx6-7qf9 actively exploited in the wild?

No public exploit code has been indexed for GHSA-58fp-mcx6-7qf9 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-58fp-mcx6-7qf9?

GHSA-58fp-mcx6-7qf9 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 42th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-58fp-mcx6-7qf9?

GHSA-58fp-mcx6-7qf9 is classified as Path Traversal (CWE-22). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was GHSA-58fp-mcx6-7qf9 published, and has it been updated?

GHSA-58fp-mcx6-7qf9 was published on August 20, 2026 and was last updated on August 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘

🐘 Packagist

Not in CISA KEV

MEDIUM severity

GHSA-58fp-mcx6-7qf9 — winter/wn-backend-module

MEDIUMFix: wintercms/storm@af77033

GHSA-58fp-mcx6-7qf9 is a medium-severity (CVSS 4.9) Path Traversal vulnerability in winter/wn-backend-module. A fix is available for winter/wn-backend-module — see the affected versions and patch details below.

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

Also known asCVE-2026-63179

Published

Aug 20, 2026

Updated

Aug 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-58fp-mcx6-7qf9.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs42th percentile — riskier than 42% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-58fp-mcx6-7qf9 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 382,621 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐘winter/wn-backend-module

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

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

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).

Workarounds

If you cannot upgrade, apply https://github.com/wintercms/storm/commit/af770331c683e628533a6ec2991285d6e10a4d6c and https://github.com/wintercms/winter/commit/130f0ea43e9228bf0d129b481da1cdfbcc4b4456 manually. As an interim mitigation, remove cms.manage_assets from any non-trusted role and clear any non-empty value from the Brand Settings custom_css and Editor Settings html_custom_styles fields.

References

See https://github.com/octobercms/october/security/advisories/GHSA-3888-q23f-x7qh for the related (but distinct in scope) October CMS advisory addressing the theme-asset compiler path. The Brand/Editor/Mail Brand Settings sinks reported in this advisory are not covered by the October patch.

Credit to Nguyen Van Hiep (@hypnguyen1209) from Lo Security for reporting the issue.

For more information

If you have any questions or comments about this advisory:

Email us at [email protected]

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`winter/wn-backend-module`	all versions	1.2.13`composer require winter/wn-backend-module:^1.2.13`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for winter/wn-backend-module, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update winter/wn-backend-module to 1.2.13 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-58fp-mcx6-7qf9 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

### 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. -