Craft CMS GraphQL entry mutation resolvers (saveEntry, deleteEntry) read the siteId argument directly from the GraphQL arguments without first passing it through the ArgumentManager’s prepareArguments() method, which enforces site‑scope filtering. As a result, an attacker who controls a token scoped to Site A can supply a siteId that targets Site B and create, modify, or delete entries there. This bypass of the schema’s allowed‑sites check allows cross‑site data manipulation, compromising confidentiality, integrity, and availability of content on the unauthorized site.

Craft CMS installations that use the CMS product (Craft CMS CMS) are affected. The vulnerability exists in all versions of Craft CMS prior to the 5.10.11 release; upgrading to 5.10.11 or later applies the fix.

The CVSS score of 8.7 indicates high severity. The EPSS score is not available, so the current exploit probability cannot be quantified, and the vulnerability is not listed in CISA’s KEV catalog. The likely attack vector is via the public GraphQL endpoint: an authenticated user with a Site‑scoped token can craft a mutation that includes a siteId referring to a different site. Once the mutation is executed, the target site’s entries are altered or removed without authorization.