{
  "canonical_id": "nextjs--CVE-2026-27977",
  "system_id": "nextjs",
  "display_name": "Next.js",
  "category": "frameworks",
  "advisory_mode": "core",
  "title": "Next.js: null origin can bypass dev HMR websocket CSRF checks",
  "summary": "## Summary\nIn `next dev`, cross-site protection for internal websocket endpoints could treat `Origin: null` as a bypass case even if [`allowedDevOrigins`](https://nextjs.org/docs/app/api-reference/config/next-config-js/allowedDevOrigins) is configured, allowing privacy-sensitive/opaque contexts (for example sandboxed documents) to connect unexpectedly.\n\n## Impact\nIf 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.\nApps without a configured [`allowedDevOrigins`](https://nextjs.org/docs/app/api-reference/config/next-config-js/allowedDevOrigins) still allow connections from any origin.\n\n## Patches\nFixed by validating `Origin: null` through the same cross-site origin-allowance checks used for other origins.  \n\n## Workarounds\nIf upgrade is not immediately possible:\n- Do not expose `next dev` to untrusted networks.\n- Block websocket upgrades to `/_next/webpack-hmr` when `Origin` is `null` at your proxy.",
  "published_at": "2026-03-17T15:29:48Z",
  "updated_at": "2026-03-17T15:46:26.028580Z",
  "severity": "medium",
  "cvss_score": 4.0,
  "exploit_status": "unknown",
  "source_confidence": "official",
  "official_source_url": "https://github.com/vercel/next.js/security/advisories/GHSA-jcc7-9wpm-mj36",
  "secondary_source_urls": [
    "https://github.com/vercel/next.js/commit/862f9b9bb41d235e0d8cf44aa811e7fd118cee2a",
    "https://github.com/vercel/next.js",
    "https://github.com/vercel/next.js/releases/tag/v16.1.7"
  ],
  "aliases": [
    "CVE-2026-27977",
    "GHSA-jcc7-9wpm-mj36"
  ],
  "cve_ids": [
    "CVE-2026-27977"
  ],
  "ghsa_ids": [
    "GHSA-jcc7-9wpm-mj36"
  ],
  "osv_ids": [
    "GHSA-jcc7-9wpm-mj36"
  ],
  "affected_versions": [
    "introduced=16.0.1, fixed<16.1.7"
  ],
  "fixed_versions": [
    "16.1.7"
  ],
  "package_name": "next",
  "render_markdown": true,
  "case_path": "07-framework-security/frameworks/nextjs/cases/nextjs-cve-2026-27977.md",
  "secure_code_topics": [
    "authz-server-side-recheck",
    "proxy-trust-boundary",
    "token-cookie-storage"
  ],
  "status": "generated",
  "triage_reasons": [],
  "verification_status": "triage-manual",
  "verification_mode": "synthetic",
  "last_verified_at": null,
  "last_run_id": null,
  "evidence_bundle": null,
  "historical_status": null,
  "latest_status": null,
  "browser_evidence": {
    "required": false,
    "present": false,
    "refs": []
  },
  "repro_profile_id": "nextjs-proxy-boundary",
  "artifact_mode": "official-source",
  "blocked_reason": null,
  "metadata": {
    "source_names": [
      "OSV Next.js"
    ],
    "source_kinds": [
      "osv-batch"
    ],
    "candidate_count": 1
  }
}