vulnerability / NVI-00003433 / Revision 2
Winter: Stored XSS through cached Brand Settings and Editor Settings custom styles
GitHub lists this reviewed advisory for winter/wn-backend-module. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
4.5 medium
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
winter/wn-backend-module
source listed<= 1.2.13
### Impact Users with the `backend.manage_branding` ("Customize the back-end") or `backend.manage_editor` ("Manage global code editor preferences") permission can provide custom CSS through **Settings → Customize Backend → Styles** or **Settings → Editor Settings → Markup Styles** that is compiled through the LESS CSS parser and rendered on every backend page. v1.2.13 addressed CVE-2026-32257 and CVE-2026-32258 by applying `strip_tags()` to the compiled output of `BrandSetting::renderCss()` and `EditorSetting::renderCss()`. That fix was incomplete. Both methods cache the **raw** compiler output with `Cache::forever()` and applied `strip_tags()` only to the value returned on a cache miss, so every subsequent cache hit returned the unsanitized value directly into the backend `` element. The first page render after saving therefore appears sanitized while priming an unsafe cache entry, and the stored XSS remains exploitable from the second render onwards. Because the custom styles partial is included by both the standard backend layout head and the backend authentication layout, an injected payload also renders on the unauthenticated backend sign-in, password restore, and pa
winter/wn-backend-module
source listedECOSYSTEM: introduced 0; fixed 1.2.14
### Impact Users with the `backend.manage_branding` ("Customize the back-end") or `backend.manage_editor` ("Manage global code editor preferences") permission can provide custom CSS through **Settings → Customize Backend → Styles** or **Settings → Editor Settings → Markup Styles** that is compiled through the LESS CSS parser and rendered on every backend page. v1.2.13 addressed CVE-2026-32257 and CVE-2026-32258 by applying `strip_tags()` to the compiled output of `BrandSetting::renderCss()` and `EditorSetting::renderCss()`. That fix was incomplete. Both methods cache the **raw** compiler output with `Cache::forever()` and applied `strip_tags()` only to the value returned on a cache miss, so every subsequent cache hit returned the unsanitized value directly into the backend `` element. The first page render after saving therefore appears sanitized while priming an unsafe cache entry, and the stored XSS remains exploitable from the second render onwards. Because the custom styles partial is included by both the standard backend layout head and the backend authentication layout, an injected payload also renders on the unauthenticated backend sign-in, password restore, and pa
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
- vendor patch
The original advisory lists fixed boundaries 1.2.14 for winter/wn-backend-module. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-5cwr-5jxg-pcf6 ↗
GitHub Advisory Database · vendor advisory
Observed . GitHub Advisory Database; CC-BY-4.0. Each advisory links its original attribution. Null normalizes fields.
- GHSA-5cwr-5jxg-pcf6 ↗
GitHub Advisory Database via OSV · vendor advisory
Observed . GitHub-origin advisory, CC-BY-4.0; OSV is an aggregate copy, not independent corroboration.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 2 ·
Source facts changed; compare the preserved prior revision.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.