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CVE-2026-32258 high CVSS 8.1

Cross-Site Scripting (XSS) in winter/wn-backend-module (CVE-2026-32258)

Summary

Cross-site scripting in winter/wn-backend-module (CVE-2026-32258). Confidential information can be exposed externally. Exploitable via backend.manage_editor. Mitigation: upgrade to 1.2.13 or later.

Original description

The description as published by the source.

Impact

Authenticated Backend Users with the backend.manage_editor ("Manage editor settings") permission can provide custom styles through Settings → Editor Settings → Markup Styles that are compiled through the LESS CSS parser and rendered on every backend page. Previously, the compiled output was not sanitized, which could have allowed a stored XSS attack.

Although this is a valid security issue, it's important to note that its severity is relatively low. To exploit the vulnerability, an attacker would already need to have trusted access to the Winter CMS backend with a specific administrative permission. The Winter CMS maintainers recommend that the backend.manage_editor permission only be granted to trusted administrators and developers.

A related issue exists in the custom CSS field at Settings → Customize Backend → Styles (backend.manage_branding permission), which uses the same rendering mechanism and is addressed separately.

All users are advised to update to the latest version to ensure their systems remain secure.

Patches

This issue has been patched in v1.2.13. The renderCss() method now applies strip_tags() to compiled CSS output before returning it.

Workarounds

Apply [https://github.com/wintercms/wi…

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-2026-32258 has been found in winter/wn-backend-module.
Attackers can target a specific entry point like backend.manage_editor over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.1/10.
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-2026-32258" on the vendor's site.

CVE-2026-32258 (winter/wn-backend-module) — CWE-79 / CVSS v3 8.1
Attack vector: remote (network-reachable)
Attack surface: backend.manage_editor / backend.manage_branding
Patched: 1.2.13 — apply immediately
Workaround: Apply https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720 manually if unable to upgrade to v1.2.13.
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

Cross-site scripting (XSS) (CWE-79) exists in winter/wn-backend-module. Attackers reach the vulnerable code path via backend.manage_editor.

📍 Affected scope

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

🔥 Severity

Severity: High (CVSS 8.1/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.2.13.

🛡️ Workaround

Workaround: Apply https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720 manually if unable to upgrade to v1.2.13.

🔍 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 
    Apply [https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720](https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720) manually if unable to upgrade to v1.2.13.

    パッチが適用されるまでの応急処置として、Apply https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720 manually if unable to upgrade to v1.2.13. 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":"1.2.10"},{"fixed":"1.2.13"}]}]

References

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