XSS in Craftcms Cms
CVE-2026-31859
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.
Vulnerability class: XSS (Cross-Site Scripting)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (15.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 15th percentile — 15.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Craftcms Cms — versions >= 4.15.3, < 4.17.3, >= 5.7.5, < 5.9.7
- Craftcms Craft Cms
Weakness classification (CWE)
References
- github.com/craftcms/cms/security/advisories/GHSA-fvwq-45qv-xvhv (Patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-31859?
- CVE-2026-31859 is a medium-severity vulnerability in Craftcms Cms, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2026-03-11.
- How severe is CVE-2026-31859?
- Medium severity. CVSS v3 base score is 6.1 out of 10.