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GHSA-v7cf-8gh9-gxmj

HighCVSS 8.1 / 10

Published Aug 12, 2026·Last modified Aug 12, 2026

Affected Components(1)

winter/wn-backend-module

< 1.2.13

Description

Impact

Users with the backend.manage_branding ("Customize the back-end") permission can provide custom CSS through Settings → Customize Backend → Styles that is 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_branding permission only be granted to trusted administrators and developers.

A related issue exists in the custom styles field at Settings → Editor Settings → Markup Styles (backend.manage_editor 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.

Workarounds

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

Resources

CVE-2025-61676 (identical vulnerability in October CMS, patched in v3.7.13 and v4.0.12)

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Risk Scores

Base Score

8.1

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs high-level or administrative privileges. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data.

Threat Intelligence

7.4

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS

0.38%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit

Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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