CVE-2026-64643 vercel CVE debrief

Who should care

Developers and administrators using Next.js applications with App Router and Server Actions should be aware of this vulnerability. Affected users should update to versions 15.5.21 or 16.2.11 to mitigate the issue. Additionally, users should review and update affected applications, monitor for publicly exposed client artifacts, and implement additional authentication measures for sensitive endpoints.

Technical summary

The vulnerability exists in Next.js applications using App Router, Server Actions (use server), or cache endpoints. Server Action IDs can be disclosed to unauthenticated users via publicly served client artifacts, such as static chunks containing action references. This issue has been fixed in versions 15.5.21 and 16.2.11. The disclosure of Server Action IDs can potentially bypass authentication on pages where these endpoints are used, and it is typically a recon/enumeration primitive that can increase risk when combined with other weaknesses.

Defensive priority

Medium priority for Next.js application developers and administrators, especially those using App Router and Server Actions, to update to fixed versions and implement additional security measures.

Recommended defensive actions

• Update to Next.js version 15.5.21 or 16.2.11
• Review and update affected applications using App Router and Server Actions
• Monitor for publicly exposed client artifacts
• Implement additional authentication measures for sensitive endpoints
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record was published on 2026-07-27T18:16:59.160Z and last modified on 2026-07-27T19:17:21.237Z. The NVD entry is currently in the 'Received' status. This information is based on the provided source corpus and may not reflect the current status of the vulnerability. Users should verify the information with the official CVE record and NVD entry for the most up-to-date details. The vulnerability affects Next.js versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10, and it allows Server Action IDs to be disclosed to unauthenticated users via publicly served client artifacts.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.