Keystone CMS CVE-2026-63421

The target must be running @keystone-6/core prior to version 6.5.3 with the graphql.maxTake option configured - without this option, all take values are unbounded by design and the comparison is moot. The GraphQL API endpoint must be network-reachable by the attacker; per CVSS PR:N, no authentication is required, meaning the endpoint must accept unauthenticated queries for full-severity exploitation. The bypass works on both top-level list queries (e.g., posts(take: -N)) and relationship sub-queries (e.g., user { posts(take: -N) }), so any exposed resolver with a relationship field compounds the risk. Exploitation is limited when GraphQL access is gated behind authentication, restricted to internal networks, or when graphql.maxTake is not configured (though the latter means no limit exists at all). Non-default deployment topologies that place the GraphQL API behind an authenticated API gateway are not affected by unauthenticated exploitation.

The CVSS 7.5 score with vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H accurately reflects real-world risk for publicly exposed deployments. Attack complexity is genuinely low - exploitation requires only a valid GraphQL query with a negative integer, a technique derivable from reading the public advisory and test cases in PR #9859. There is no confidentiality or integrity impact confirmed, limiting the blast radius to availability. KEV status is not listed, meaning active exploitation in the wild has not been confirmed by CISA. EPSS score was not provided in the input data. The 'Authentication Bypass' tag included in CVE metadata is partially misleading - this bypasses a record-count safeguard, not authentication controls. Deployments that restrict GraphQL API access to authenticated sessions or internal networks face substantially reduced risk, as PR:N exploitation requires the endpoint to be reachable by the attacker. For fully public-facing Keystone deployments, this is a credible DoS vector requiring immediate patching.

An unauthenticated attacker sends a GraphQL query such as { posts(take: -999999) { id title body author { id } } } to a public-facing Keystone endpoint. The unpatched (take ?? Infinity) > maxTake guard passes because -999999 is less than, not greater than, any positive maxTake value, so the database query executes without a record limit. The server then attempts to stream an unbounded result set, exhausting database connections, application memory, or CPU, degrading or denying service to legitimate users. No specific public exploit tool has been identified, though the technique requires only knowledge of GraphQL syntax and the public advisory.