CVE-2026-50281Craft CMS: Mass assignment via id in newAttributes during bulk duplicate overwrites existing elements

Official description

Craft CMS is a content management system (CMS). Versions 5.7.0 and above, prior to 5.9.21 contain a mass-assignment flaw in the bulk-duplicate element action. An attacker who is only able to duplicate their own entires can submit an arbitrary id through the newAttributes request parameter. The duplication routine overrides its own id = null reset with that value and writes the attacker's attributes into the victim's existing entry row. ElementsController::beforeAction() pulls the request body into $this->_attributes and rejects requests that ship an id or canonicalId key at the top level, actionBulkDuplicate(), reads a separate newAttributes array and passes it straight through to the service layer. Elements::duplicateElement() clones the source element, sets id to null, and then hands the attacker's array to Craft::configure(), which overwrites the reset id with any numeric value inside $newAttributes. PHP Yii's saveElement() then performs an UPDATE against the row with that primary key instead of an INSERT. The attackers's title, slug, authorId, postDate, and UID land on the victim's entry. safeAttributes() on Entry includes id because the base element model exposes it, so the Collection::only() filter does not strip it. This issue has been fixed in version 5.9.21.

Affected packages & fixed versions

Affected products (as reported)

References

• https://github.com/craftcms/cms/security/advisories/GHSA-x5m4-g2cq-52pq x_refsource_CONFIRM
• https://github.com/craftcms/cms/commit/8f6587c25050bbb6e080d59c71f6bb8932fc8600 x_refsource_MISC