vulnerability / NVI-00001950 / Revision 3
CraftCMS vulnerable to reflective XSS via incomplete return URL sanitization
OSV carries this publisher advisory for craftcms/cms, craftcms/cms. This is an aggregated source copy; consult the original publisher and compare update dates.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
6.1 MEDIUM (3.1)
nvd@nist.gov severity; no combined Null risk score.
6.9 MEDIUM (4.0)
security-advisories@github.com severity; no combined Null risk score.
0.192%
FIRST EPSS model v2026.06.15; exploitation probability over 30 days, percentile 0.08927. Missing scores are unknown.
As of · FIRST EPSS
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
craftcms/cms
source listedECOSYSTEM: introduced 4.15.3; fixed 4.17.3
### Summary 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. ### Details The patched code in is: ```php public function setReturnUrl($url): void { parent::setReturnUrl(strip_tags($url)); } ``` `strip_tags()` removes HTML tags (e.g., ``, ``) from a string, but it is **not** a URL sanitizer. When the sanitized return URL is subsequently rendered in an `href` attribute context (e.g., ``), the following dangerous payloads survive `strip_tags()` completely unmodified: 1. **`javascript:` protocol URLs** -- `javascript:alert(document.cookie)` contains no HTML tags, so `strip_tags()` returns it verbatim. When placed in an `href`, clicking the link executes the JavaScript. 2. **`data:` URIs** -- `data:text/html;base64,PHN
craftcms/cms
source listedECOSYSTEM: introduced 5.7.5; fixed 5.9.7
### Summary 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. ### Details The patched code in is: ```php public function setReturnUrl($url): void { parent::setReturnUrl(strip_tags($url)); } ``` `strip_tags()` removes HTML tags (e.g., ``, ``) from a string, but it is **not** a URL sanitizer. When the sanitized return URL is subsequently rendered in an `href` attribute context (e.g., ``), the following dangerous payloads survive `strip_tags()` completely unmodified: 1. **`javascript:` protocol URLs** -- `javascript:alert(document.cookie)` contains no HTML tags, so `strip_tags()` returns it verbatim. When placed in an `href`, clicking the link executes the JavaScript. 2. **`data:` URIs** -- `data:text/html;base64,PHN
03 / Response
What to do next
- vendor patch
The original advisory lists fixed boundaries 4.17.3 for craftcms/cms. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- vendor patch
The original advisory lists fixed boundaries 5.9.7 for craftcms/cms. Confirm the publisher’s latest guidance.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database via OSV
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. FIRST EPSS
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
- NVD lastModified does not establish freshness of every associated CPE record.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-fvwq-45qv-xvhv ↗
GitHub Advisory Database via OSV · vendor advisory
Observed . GitHub-origin advisory, CC-BY-4.0; OSV is an aggregate copy, not independent corroboration.
- CVE-2026-31859 ↗
NIST National Vulnerability Database · official catalog
Observed . This product uses data from the NVD API but is not endorsed or certified by the NVD.
- CVE-2026-31859 ↗
FIRST EPSS · official catalog
Observed . FIRST EPSS; probability of exploitation in the next 30 days, not local compromise. Dataset date/model retained; FIRST services terms apply.
Public revision history
Only published revisions appear here. Routine fetches do not create a material-change event.
- Revision 3 ·
Source facts changed; compare the preserved prior revision.
- Revision 2 ·
Dated EPSS estimate updated; this is not a new disclosure or proof of exploitation.
- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.