CVE-2026-27977

Summary

Next.js is a React framework for building full-stack web applications. Starting in version 16.0.1 and prior to version 16.1.7, in next dev, cross-site protection for internal websocket endpoints could treat Origin: null as a bypass case even if allowedDevOrigins is configured, allowing privacy-sensitive/opaque contexts (for example sandboxed documents) to connect unexpectedly. If a dev server is reachable from attacker-controlled content, an attacker may be able to connect to the HMR websocket channel and interact with dev websocket traffic. This affects development mode only. Apps without a configured allowedDevOrigins still allow connections from any origin. The issue is fixed in version 16.1.7 by validating Origin: null through the same cross-site origin-allowance checks used for other origins. If upgrading is not immediately possible, do not expose next dev to untrusted networks and/or block websocket upgrades to /_next/webpack-hmr when Origin is null at the proxy.

Affected Software

VendorProductVersion RangeStatus
vercelnext.js>= 16.0.1, < 16.1.7affected

Weaknesses

  • CWE-1385: CWE-1385: Missing Origin Validation in WebSockets

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: no
    • Technical Impact: partial

References