By manipulating the siteId parameter in GraphQL requests, an attacker can create, modify, or delete entries, categories, tags, and assets that they should not have access to. Because this bypasses site-level access controls, it permits cross-site data corruption and potential unauthorized information exposure or service disruption. This vulnerability impacts installations utilizing multi-site configurations where strict tenant isolation is required. Organizations should update to version 5.11.0 or later to ensure that site-scoped tokens are correctly validated before mutation operations.

Attack Chain

1. The attacker obtains a valid, site-scoped GraphQL API token for a specific site in a multi-site Craft CMS instance.
2. The attacker identifies the siteId of a target site that is not included in the scope of their current token.
3. The attacker crafts a GraphQL mutation request (e.g., createEntry, deleteEntry, or saveAsset) targeting the CMS GraphQL endpoint.
4. The attacker injects the siteId of the target site into the mutation parameters.
5. The server processes the GraphQL request without enforcing the requireAllowedSite() check for the provided siteId.
6. The CMS executes the mutation using the provided siteId, resulting in unauthorized data modification or deletion on the target site.

Impact

Successful exploitation allows for arbitrary unauthorized mutations across sites within a single Craft CMS installation. This can result in the deletion of critical business content, unauthorized injection of data, and the compromise of categories, tags, and assets shared across sites. The vulnerability is assigned a CVSS score of 9.8, reflecting the significant risk of unauthorized modification and potential service disruption for enterprise environments utilizing multi-site CMS architectures.

Recommendation

• Patch the instance by upgrading to Craft CMS version 5.11.0 or later immediately to resolve CVE-2026-112776.
• Audit application logs for POST requests to the GraphQL endpoint that contain unusual or unexpected siteId parameters associated with site-scoped tokens.
• Implement egress monitoring for the web server to detect unusual mutation patterns if patching is delayed.
• Review GraphQL token scope assignments to ensure the principle of least privilege is applied to all API keys and user tokens.