CVE-2026-31859: craftcms cms Cross-site Scripting

Vulnerability summary

CVE-2026-31859 is a medium (CVSS 6.9) Cross-site Scripting vulnerability in craftcms cms. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 17% of scored vulnerabilities.

Timeline

1. 11-03-2026
   PublishedVulnerability first disclosed.
2. 12-03-2026
   Last modifiedVulnerability information updated.

Description

Craft is a content management system (CMS). The fix for CVE-2025-35939 in craftcms/cms introduced a strip_tags() call in src/web/User.php to sanitize return URLs before they are stored in the session. However, strip_tags() only removes HTML tags (angle brackets) -- it does not inspect or filter URL schemes. Payloads like javascript:alert(document.cookie) contain no HTML tags and pass through strip_tags() completely unmodified, enabling reflected XSS when the return URL is rendered in an href attribute. This vulnerability is fixed in 5.9.7 and 4.17.3.

• 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.