Unrated

Stored XSS in Winter CMS backend custom styles

IdentifiersCVE-2026-32258CWE-79

CVE-2026-32258 is a stored cross-site scripting vulnerability in the Winter CMS backend module affecting custom editor and branding style handling. The flaw stems from insufficient sanitization of compiled LESS/CSS output in backend style rendering, including incomplete handling of cached renderCss() output. An authenticated backend user with elevated editor or branding-related permissions can inject malicious markup through custom style configuration, causing attacker-controlled content to be stored and later rendered in backend pages. Available information indicates the issue affected backend pages broadly and, after cache priming, could also impact backend authentication-related pages such as sign-in, password restore, and password reset views.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows an authenticated attacker with the relevant backend permissions to persistently inject script-capable content into Winter CMS backend pages. This can lead to execution of arbitrary JavaScript in the browser context of backend users, including administrators, enabling session theft, request forgery, administrative action execution, credential capture, and broader compromise of the CMS administrative interface. In the cache-poisoning variant, the malicious content may also be rendered on backend authentication pages after the poisoned cache entry has been created.

Mitigation

If you can’t patch tonight, do this now.

Limit the backend.manage_editor and backend.manage_branding permissions to highly trusted administrators and developers only. Review and remove any untrusted custom style definitions from backend configuration. Clear application caches to temporarily remove poisoned cached output, recognizing that this does not fully resolve the issue without the code fix. Monitor backend pages for unexpected injected markup or script behavior until the patched version is deployed.

Remediation

Patch, then assume compromise.

Upgrade the Winter CMS backend module package winter/wn-backend-module to version 1.2.14 or later. Version 1.2.13 addressed sanitization of compiled CSS output, while 1.2.14 additionally sanitizes cached renderCss() values on read and neutralizes previously poisoned cache entries. If an immediate upgrade is not possible, apply the vendor patch that sanitizes compiled and cached CSS output and then clear application caches to remove poisoned cached content.

PUBLIC EXPLOITS

Exploits

No public exploits tracked yet. Mallory keeps watching.

VALID 0 / 0 TOTALView more in app

No public exploit code observed for this vulnerability.

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

WintercmsWn-Backend-Moduleapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

No public activity tracked yet. Mallory keeps watching.

0 SOURCESView more in app

No public activity observed for this vulnerability.

What this page doesn’t show

The version that knows your environment.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity