CVE-2026-63421 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in @keystone-6/core. A fix is available for @keystone-6/core — see the affected versions and patch details below.
Keystone: `graphql.maxTake` bypass with negative `take`
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-63421.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-63421 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 384,189 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@keystone-6/corenpmDescription
Summary
The value of graphql.maxTake can be bypassed by providing a negative input.
This can be used to exceed the developer's intended graphql.maxTake value, allowing queries to return results in excess of the graphql.maxTake value set.
Impact
This affects any project relying on graphql.maxTake to bound the number of items returned per query.
Patches
This issue has been patched in @keystone-6/core version 6.5.3.
If you cannot patch, you can workaround this by restricting take input values in your GraphQL queries to the bounded value, or by blocking negative values.
Credit
This issue was found by Haxset's Security Scanner and validated by their team.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @keystone-6/core | all versions | 6.5.3npm install @keystone-6/core@6.5.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @keystone-6/core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @keystone-6/core to 6.5.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-63421 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2026-63421 in your dependencies?
Find it across npm, including transitive dependencies.