{"id":"CVE-2026-27977","summary":"Next.js: null origin can bypass dev HMR websocket CSRF checks","details":"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.","aliases":["GHSA-jcc7-9wpm-mj36"],"modified":"2026-04-10T05:41:03.753784Z","published":"2026-03-17T23:56:24.631Z","database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27977.json","cwe_ids":["CWE-1385"],"cna_assigner":"GitHub_M"},"references":[{"type":"WEB","url":"https://github.com/vercel/next.js/releases/tag/v16.1.7"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27977.json"},{"type":"ADVISORY","url":"https://github.com/vercel/next.js/security/advisories/GHSA-jcc7-9wpm-mj36"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27977"},{"type":"FIX","url":"https://github.com/vercel/next.js/commit/862f9b9bb41d235e0d8cf44aa811e7fd118cee2a"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/vercel/next.js","events":[{"introduced":"e08402bfad8db05b0df820daf4f08c9c65ab1f7b"},{"fixed":"bdf3e3577a6d55ea186a48238d61fbd8da07a626"}]}],"versions":["v16.0.1","v16.0.2-canary.0","v16.0.2-canary.1","v16.0.2-canary.10","v16.0.2-canary.11","v16.0.2-canary.12","v16.0.2-canary.13","v16.0.2-canary.14","v16.0.2-canary.15","v16.0.2-canary.16","v16.0.2-canary.17","v16.0.2-canary.18","v16.0.2-canary.19","v16.0.2-canary.2","v16.0.2-canary.20","v16.0.2-canary.21","v16.0.2-canary.22","v16.0.2-canary.23","v16.0.2-canary.24","v16.0.2-canary.25","v16.0.2-canary.26","v16.0.2-canary.27","v16.0.2-canary.28","v16.0.2-canary.29","v16.0.2-canary.3","v16.0.2-canary.30","v16.0.2-canary.31","v16.0.2-canary.32","v16.0.2-canary.33","v16.0.2-canary.34","v16.0.2-canary.4","v16.0.2-canary.5","v16.0.2-canary.6","v16.0.2-canary.7","v16.0.2-canary.8","v16.0.2-canary.9","v16.1.0","v16.1.0-canary.0","v16.1.0-canary.1","v16.1.0-canary.10","v16.1.0-canary.11","v16.1.0-canary.12","v16.1.0-canary.13","v16.1.0-canary.14","v16.1.0-canary.15","v16.1.0-canary.16","v16.1.0-canary.17","v16.1.0-canary.18","v16.1.0-canary.19","v16.1.0-canary.2","v16.1.0-canary.20","v16.1.0-canary.21","v16.1.0-canary.22","v16.1.0-canary.23","v16.1.0-canary.24","v16.1.0-canary.25","v16.1.0-canary.26","v16.1.0-canary.27","v16.1.0-canary.28","v16.1.0-canary.29","v16.1.0-canary.3","v16.1.0-canary.30","v16.1.0-canary.31","v16.1.0-canary.32","v16.1.0-canary.33","v16.1.0-canary.34","v16.1.0-canary.4","v16.1.0-canary.5","v16.1.0-canary.6","v16.1.0-canary.7","v16.1.0-canary.8","v16.1.0-canary.9","v16.1.1","v16.1.2","v16.1.3","v16.1.4","v16.1.5","v16.1.6"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-27977.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"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"}]}