# CVE-2026-27977: Next.js: null origin can bypass dev HMR websocket CSRF checks

> CVE-2026-27977: Next.js: null origin can bypass dev HMR websocket CSRF checks. CVSS 5.4 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-27977
Last updated: 2026-06-17T10:28:00Z

- Published: 2026-03-17 23:56 UTC · Updated: 2026-06-17 10:28 UTC · Assigner: GitHub\_M
- CVSS: 5.4 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
- EPSS: 0.18%, 7th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-1385

## 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 vendors and products

- vercel: next.js

## Tracked companies

- [Vercel](https://rewindex.com/company/vercel.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-27977)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-27977)
- [https://github.com/vercel/next.js/commit/862f9b9bb41d235e0d8cf44aa811e7fd118cee2a](https://github.com/vercel/next.js/commit/862f9b9bb41d235e0d8cf44aa811e7fd118cee2a)
- [https://github.com/vercel/next.js/releases/tag/v16.1.7](https://github.com/vercel/next.js/releases/tag/v16.1.7)
- [https://github.com/vercel/next.js/security/advisories/GHSA-jcc7-9wpm-mj36](https://github.com/vercel/next.js/security/advisories/GHSA-jcc7-9wpm-mj36)

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_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


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Canonical: https://rewindex.com/cve/CVE-2026-27977 · Markdown: https://rewindex.com/cve/CVE-2026-27977.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-27977 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T02:15:06.158Z