CVE-2026-33889
ApostropheCMS: Stored XSS via CSS Custom Property Injection in `@apostrophecms/color-field` Escaping Style Tag Context
Description
ApostropheCMS is an open-source Node.js content management system. Versions 4.28.0 and prior contain a stored cross-site scripting vulnerability in the @apostrophecms/color-field module, where color values prefixed with -- bypass TinyColor validation intended for CSS custom properties, and the launder.string() call performs only type coercion without stripping HTML metacharacters. These unsanitized values are then concatenated directly into <style> tags both in per-widget style elements rendered for all visitors and in the global stylesheet rendered for editors, with the output marked as safe HTML. An editor can inject a value which closes the style tag and executes arbitrary JavaScript in the browser of every visitor to any page containing the affected widget. This enables mass session hijacking, cookie theft, and privilege escalation to administrative control if an admin views draft content. This issue has been fixed in version 4.29.0.
INFO
Published Date :
April 15, 2026, 8:16 p.m.
Last Modified :
April 20, 2026, 5:03 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update ApostropheCMS to version 4.29.0.
- Review and sanitize all color field inputs.
- Ensure output HTML is properly escaped.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33889.
| URL | Resource |
|---|---|
| https://github.com/apostrophecms/apostrophe/commit/6a89bdb7acdb2e1e9bf1429961a6ba7f99410481 | Patch |
| https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-97v6-998m-fp4g | Exploit Mitigation Vendor Advisory |
| https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-97v6-998m-fp4g | Exploit Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33889 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33889
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33889 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-33889 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 20, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:apostrophecms:apostrophecms:*:*:*:*:*:*:*:* versions up to (excluding) 4.29.0 Added Reference Type GitHub, Inc.: https://github.com/apostrophecms/apostrophe/commit/6a89bdb7acdb2e1e9bf1429961a6ba7f99410481 Types: Patch Added Reference Type CISA-ADP: https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-97v6-998m-fp4g Types: Exploit, Mitigation, Vendor Advisory Added Reference Type GitHub, Inc.: https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-97v6-998m-fp4g Types: Exploit, Mitigation, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 16, 2026
Action Type Old Value New Value Added Reference https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-97v6-998m-fp4g -
New CVE Received by [email protected]
Apr. 15, 2026
Action Type Old Value New Value Added Description ApostropheCMS is an open-source Node.js content management system. Versions 4.28.0 and prior contain a stored cross-site scripting vulnerability in the @apostrophecms/color-field module, where color values prefixed with -- bypass TinyColor validation intended for CSS custom properties, and the launder.string() call performs only type coercion without stripping HTML metacharacters. These unsanitized values are then concatenated directly into <style> tags both in per-widget style elements rendered for all visitors and in the global stylesheet rendered for editors, with the output marked as safe HTML. An editor can inject a value which closes the style tag and executes arbitrary JavaScript in the browser of every visitor to any page containing the affected widget. This enables mass session hijacking, cookie theft, and privilege escalation to administrative control if an admin views draft content. This issue has been fixed in version 4.29.0. Added CVSS V3.1 AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N Added CWE CWE-79 Added Reference https://github.com/apostrophecms/apostrophe/commit/6a89bdb7acdb2e1e9bf1429961a6ba7f99410481 Added Reference https://github.com/apostrophecms/apostrophe/security/advisories/GHSA-97v6-998m-fp4g