CVE-2026-63421: Keystone GraphQL maxTake bypass with negative values

CVE-2026-63421 · Severity: high · CVSS 7.5 · Published 2026-08-21

Keystone is a CMS and data platform that provides GraphQL API query capabilities. A vulnerability in query result limiting allows attackers to bypass the `graphql.maxTake` configuration by submitting negative values, enabling them to retrieve arbitrarily large result sets and potentially cause denial of service through resource exhaustion or data exfiltration.

Technologies: @keystone-6/core (npm). Vendors: npm.

Quick answers

Is CVE-2026-63421 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-63421 being exploited in the wild.
How severe is CVE-2026-63421?
High severity, with a CVSS score of 7.5, published 21 August 2026.
Which products and versions are affected?
@keystone-6/core (npm) <= 6.5.2, SEMVER:introduced=0,fixed=6.5.3.
Is there a fix for CVE-2026-63421?
Yes. @keystone-6/core (npm): upgrade to 6.5.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-63421 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-63421?
Check whether you run @keystone-6/core (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • @keystone-6/core (npm): upgrade to 6.5.3 or later
    npm install @keystone-6/core@6.5.3

Technical details

The vulnerability is an input validation flaw (CWE-20) in Keystone's GraphQL query processing, where the `take` parameter does not properly validate against negative values. The root cause appears to involve an incorrect operator condition (CWE-480) that fails to restrict negative inputs. An unauthenticated attacker can send a GraphQL query with a negative `take` parameter to bypass the developer-configured `graphql.maxTake` limit, allowing retrieval of unlimited result sets. This is exploitable over the network with no authentication required and no user interaction needed. The impact is primarily denial of service through resource exhaustion or potential data exposure. The issue was patched in version 6.5.3; users unable to patch can restrict `take` input values or block negative values at the GraphQL layer.

Affected products

  • KeystoneJS @keystone-6/core <= 6.5.2

Identifiers

  • CVE-2026-63421
  • GHSA-cqmq-8755-7xvh

Timeline

  • 2026-07-01: disclosed: Vulnerability published in GitHub Advisory Database
  • 2026-08-21: advisory: Advisory updated and published
  • 2026: patched: Patched in @keystone-6/core version 6.5.3

References

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