CVE-2026-31859 — Craft has Reflective XSS via incomplete return URL sanitization

Description (CNA)

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.

Affected (CNA)

Vendor / product	Versions
craftcms / cms	affected >= 4.15.3, < 4.17.3; affected >= 5.7.5, < 5.9.7

CWE

CWE-79, CWE-116

References

https://github.com/craftcms/cms/security/advisories/GHSA-fvwq-45qv-xvhv

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.