CVE-2026-35569: ApostropheCMS: Stored XSS in SEO Fields Leads to Authenticated API Data Exposure in ApostropheCMS

Vulnerability summary

CVE-2026-35569 is a high (CVSS 8.7) Cross-site Scripting vulnerability in apostrophecms apostrophe. EPSS estimates a 0.44% chance of exploitation in the next 30 days, higher than 37.1% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 15-04-2026
   PublishedVulnerability first disclosed.
2. 14-05-2026
   Last modifiedVulnerability information updated.

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 SEO-related fields (SEO Title and Meta Description), where user-controlled input is rendered without proper output encoding into HTML contexts including <title> tags, <meta> attributes, and JSON-LD structured data. An attacker can inject a payload such as "></title><script>alert(1)</script> to break out of the intended HTML context and execute arbitrary JavaScript in the browser of any authenticated user who views the affected page. This can be leveraged to perform authenticated API requests, access sensitive data such as usernames, email addresses, and roles via internal APIs, and exfiltrate it to an attacker-controlled server. This issue has been fixed in version 4.29.0.

• CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
• CWE-116Improper Encoding or Escaping of OutputThe product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.