PatchSiren cyber security CVE debrief
CVE-2026-64643 vercel CVE debrief
CVE-2026-64643 is a medium-severity vulnerability affecting Next.js versions 12.0.0 through 15.5.20 and 16.0.0 through 16.2.10. The issue allows Server Action IDs to be disclosed to unauthenticated users via publicly served client artifacts, potentially bypassing authentication on pages where these endpoints are used. This disclosure is typically a recon/enumeration primitive but can increase risk when combined with other weaknesses. The vulnerability has been fixed in versions 15.5.21 and 16.2.11.
- Vendor
- vercel
- Product
- next.js
- CVSS
- MEDIUM 6.3
- CISA KEV
- Not listed in stored evidence
- Original CVE published
- 2026-07-27
- Original CVE updated
- 2026-07-27
- Advisory published
- 2026-07-27
- Advisory updated
- 2026-07-27
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.
Official resources
AI-assisted PatchSiren debrief based on the supplied source corpus. The CVE record was published on 2026-07-27T18:16:59.160Z and has not been modified since then. The NVD entry is currently Received.