CVE-2026-63179

MEDIUMPre-NVD 4.94.9
EchelonGraph scoreLOW confidence

This medium-severity CVE scores 4.9 under the CNA's CVSS (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: cna:github_m
4.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: —CVSS: 4.9Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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

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) "" 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 ` block.
  • Editor Settings EditorSetting.html_custom_styles field (backend.manage_editor) — compiled inline into every backend page's 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:

CVSS v3
4.9
EG Score
4.9(low)
EG Risk
27(Track)
EG Risk 27/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity49% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
—
EPSS %ILE
—
KEV
Not listed

Published

August 20, 2026

Last Modified

August 20, 2026

Vendor Advisories for CVE-2026-63179(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Data Freshness Timeline

(refreshed 1× in last 7d / 1× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-08-20 19:42 UTCEG score recompute

Frequently asked(4)

What is CVE-2026-63179?
CVE-2026-63179 is a medium vulnerability published on August 20, 2026. Winter: Local File Inclusion through @import directives in LESS compilation of backend customizable stylesheets and theme assets Impact Affected versions of Winter CMS allow authenticated backend users with the following permissions to disclose arbitrary files readable by the PHP process by…
When was CVE-2026-63179 disclosed?
CVE-2026-63179 was first published in the National Vulnerability Database on August 20, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
What is the CVSS score of CVE-2026-63179?
CVE-2026-63179 has a CVSS v4.0 base score of 4.9 (CNA self-assessment; NVD's own analysis pending). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-63179?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-63179, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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