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CVE-2026-63179 medium CVSS 4.9

Path Traversal in winter/wn-backend-module (CVE-2026-63179)

Summary

Path traversal in winter/wn-backend-module (CVE-2026-63179). Confidential information can be exposed externally. Exploitable via BrandSetting.custom_css. Mitigation: upgrade to 1.2.13 or later.

Original description

The description as published by the source.

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…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-63179 has been found in winter/wn-backend-module.
Attackers can target a specific entry point like BrandSetting.custom_css over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 4.9/10.
What to do: upgrade winter/wn-backend-module to 1.2.13 or later.
If unsure, ask your IT team or search "winter/wn-backend-module CVE-2026-63179" on the vendor's site.

CVE-2026-63179 (winter/wn-backend-module) — CWE-22 / CVSS v3 4.9
Attack vector: remote (network-reachable) / no user interaction
Attack surface: BrandSetting.custom_css / backend.manage_branding / EditorSetting.html_custom_styles / backend.manage_editor
Patched: 1.2.13 — apply immediately
Workaround: If you cannot upgrade, apply https://github.com/wintercms/storm/commit/af770331c683e628533a6ec2991285d6e10a4d6c and https://github.com/wintercms/winter/commit/130f0ea43e9228bf0d129b481da1cdfbcc4b4456 manually.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Path traversal (CWE-22) exists in winter/wn-backend-module. Attackers reach the vulnerable code path via BrandSetting.custom_css.

📍 Affected scope

Check the vendor advisory for the affected versions of winter/wn-backend-module. Attack surface: BrandSetting.custom_css / backend.manage_branding / EditorSetting.html_custom_styles / backend.manage_editor.

🔥 Severity

Severity: Medium (CVSS 4.9/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.2.13.

🛡️ Workaround

Workaround: If you cannot upgrade, apply https://github.com/wintercms/storm/commit/af770331c683e628533a6ec2991285d6e10a4d6c and https://github.com/wintercms/winter/commit/130f0ea43e9228bf0d129b481da1cdfbcc4b4456 manually.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'winter/wn-backend-module' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'winter/wn-backend-module' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で winter/wn-backend-module を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply temporary workaround mitigate 
    If you cannot upgrade, apply https://github.com/wintercms/storm/commit/af770331c683e628533a6ec2991285d6e10a4d6c and https://github.com/wintercms/winter/commit/130f0ea43e9228bf0d129b481da1cdfbcc4b4456 manually.

    パッチが適用されるまでの応急処置として、If you cannot upgrade, apply https://github.com/wintercms/storm/commit/af770331c683e628533a6ec2991285d6e10a4d6c and https://github.com/wintercms/winter/commit/130f0ea43e9228bf0d129b481da1cdfbcc4b4456 manually. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade winter/wn-backend-module to 1.2.13

    ステージング環境で 1.2.13 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  4. 4
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

composer winter/wn-backend-module
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.2.13"}]}]
Packagist winter/wn-backend-module
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.2.13"}]}]

References

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