CVE-2026-31859
MEDIUM
GHSA-fvwq-45qv-xvhv
CVSS Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Lifecycle Timeline
3Description
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.
Analysis
Reflected XSS in Craft CMS versions before 5.9.7 and 4.17.3 allows remote attackers to execute arbitrary JavaScript in users' browsers via malicious return URLs that bypass insufficient sanitization. The vulnerability exists because the patch for a prior issue relied on strip_tags() to filter URLs, which fails to block dangerous URL schemes like javascript:. …
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Remediation
Within 30 days: Identify affected systems running src/web/User.php to sanitize return URLs and apply vendor patches as part of regular patch cycle. Verify Content-Security-Policy and output encoding.
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External POC / Exploit Code
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