CVE-2026-27978: Next.js: null origin can bypass Server Actions CSRF checks
Summary origin: null was treated as a "missing" origin during Server Action CSRF validation. As a result, requests from opaque contexts (such as sandboxed iframes) could bypass origin verification instead of being validated as cross-origin requests.
Impact An attacker could induce a victim browser to submit Server Actions from a sandboxed context, potentially executing state-changing actions with victim credentials (CSRF).
Patches Fixed by treating 'null' as an explicit origin value and enforcing host/origin checks unless 'null' is explicitly allowlisted in experimental.serverActions.allowedOrigins.
Workarounds If upgrade is not immediately possible: - Add CSRF tokens for sensitive Server Actions. - Prefer SameSite=Strict on sensitive auth cookies. - Do not allow 'null' in serverActions.allowedOrigins unless intentionally required and additionally protected.
Other sources
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, origin: null was treated as a "missing" origin during Server Action CSRF validation. As a result, requests from opaque contexts (such as sandboxed iframes) could bypass origin verification instead of being validated as cross-origin requests. An attacker could induce a victim browser to submit Server Actions from a sandboxed context, potentially executing state-changing actions with victim credentials (CSRF). This is fixed in version 16.1.7 by treating 'null' as an explicit origin value and enforcing host/origin checks unless 'null' is explicitly allowlisted in experimental.serverActions.allowedOrigins. If upgrading is not immediately possible, add CSRF tokens for sensitive Server Actions, prefer SameSite=Strict on sensitive auth cookies, and/or do not allow 'null' in serverActions.allowedOrigins unless intentionally required and additionally protected.
— NVD
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27978?
CVE-2026-27978 is considered a critical vulnerability due to its ability to bypass origin verification during Server Action CSRF validation.
How do I fix CVE-2026-27978?
To fix CVE-2026-27978, upgrade to version 16.1.7 or later of the next.js package.
What types of software are affected by CVE-2026-27978?
CVE-2026-27978 affects the next.js package versions from 16.0.1 to 16.1.6.
What impact does CVE-2026-27978 have on web applications?
CVE-2026-27978 allows attackers to induce cross-origin requests from opaque contexts, potentially leading to unauthorized actions in web applications.
Can I continue using next.js while CVE-2026-27978 exists?
It is highly recommended to mitigate the risks by upgrading or applying security patches to avoid exploitation of CVE-2026-27978.