# CVE-2026-27977

## Summary

- **CVE ID:** CVE-2026-27977
- **Severity:** LOW
- **CVSS Score:** 2.3 (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N)
- **CWE:** CWE-1385
- **Published:** Mar 17, 2026
- **Last Modified:** Mar 19, 2026

## Description

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 Products

- vercel — next.js (>= 16.0.1, < 16.1.7)

## References

- [CNA](https://github.com/vercel/next.js/security/advisories/GHSA-jcc7-9wpm-mj36)
- [CNA](https://github.com/vercel/next.js/commit/862f9b9bb41d235e0d8cf44aa811e7fd118cee2a)
- [CNA](https://github.com/vercel/next.js/releases/tag/v16.1.7)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.17%
- **EPSS Percentile:** 6.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-10._