GHSA-mp59-9rf5-93wr: 
PHP vulnerability analysis and mitigation

An unauthenticated POST /actions/graphql/api request against a GraphQL Public Schema whose Sites scope grants only site 1 can read the content of site 2. The schema is explicitly not authorized to read — by selecting the localized element field with its siteId/site argument omitted. The same field with the argument supplied (localized(siteId:2)) is correctly denied ([]), and five other legitimate paths to site 2 are also denied for the identical anonymous principal; a positive control (a temporary both-sites token) confirms that those denials are Sites-scope enforcement, not missing data.

Preconditions

• Craft multi-site install (≥2 sites).
• A GraphQL schema whose Sites scope omits ≥1 site.
• A section enabled for both sites and inside the schema’s Sections scope.
• The schema reachable: the Public Schema (anonymous), or any issued restricted token.
• No allowAdminChanges, admin session, or non-default config.
• Custom-field bodies diverge per site only for fields set to “Translate for each site” (a documented setting, and the configuration in which per-site content is independent in the first place).

Impact

An unauthenticated internet client can read the content of any site a GraphQL schema is not scoped to, so long as that site shares a section with an in-scope site — in a single request, with zero credentials (no account, no token, no cookie). Report ID: 1936