ApostropheCMS: Color field validation bypass allows stored XSS via HTML appended after rgb()/hsl() prefix

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.4 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

EPSS

• CVE-2026-112951: 0.30% estimated exploitation activity in the next 30 days; percentile 23.23 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The color field accepts any string that begins with a valid rgb() / hsl() color, because TinyColor.isValid does not anchor its match at the end of the string. An authenticated user with edit rights can store arbitrary HTML after a valid color prefix. When the stored value is rendered , the payload executes, resulting in stored XSS. Details Server-side validation of the color field relies on TinyColor: TinyColor's rgb/hsl matchers are not anchored at the end of the string, while hex matchers are. Tested with @ctrl/tinycolor | Input | isValid | |---|---| | rgb(1,2,3)<img src=x onerror=alert(1) | true | | rgb(1,2,3)</textarea<scriptalert(1)</script | true | | hsl(0,100%,50%);--x:1}</style<scriptalert(1)</script | true | | #ff0000<img src=x onerror=alert(1) | false | The value is saved to MongoDB unchanged (not normalized to hex8). Relation to GHSA-97v6-998m-fp4g GHSA-97v6 addressed CSS custom property injection escaping a <style context. The root cause (validation that accepts…

Published by the source

21 Oct 2026, 17:05 UTC

Last modified by the source

21 Oct 2026, 17:15 UTC

Source last checked

26 Oct 2026, 13:07 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-vmgj-9cwm-cf3h

2. Revision 2 · amended · 24 Oct 2026

   Amended from osv record GHSA-vmgj-9cwm-cf3h

3. Revision 1 · created · 23 Oct 2026

   Published from ghsa record GHSA-vmgj-9cwm-cf3h

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# Patch Next advisory brief: CVE-2026-112951

Advisory: ApostropheCMS: Color field validation bypass allows stored XSS via HTML appended after rgb()/hsl() prefix
IDs: CVE-2026-112951, GHSA-vmgj-9cwm-cf3h
Record: https://patchnext.com/advisories/cve-2026-112951 (revision 3, source checked 26 Oct 2026, 13:07 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: apostrophe 4.34.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm apostrophe: affected < 4.34.0; fixed in 4.34.0

## Suggested inspection (read-only)
- `npm ls apostrophe --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on apostrophe.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-vmgj-9cwm-cf3h (GitHub-reviewed advisory GHSA-vmgj-9cwm-cf3h lists affected ranges: npm apostrophe >=0 <4.34.0)
- Verified: https://osv.dev/vulnerability/GHSA-vmgj-9cwm-cf3h (OSV record GHSA-vmgj-9cwm-cf3h lists affected ranges: npm apostrophe >=0 <4.34.0 (fixed))

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