CVE-2026-27978

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.

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.

An attacker could induce a victim browser to submit Server Actions from a sandboxed context, potentially executing state-changing actions with victim credentials (CSRF).

A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones. Typical impact: state-changing actions performed as the victim without their consent.

Kodem intelligence

Fixed by treating 'null' as an explicit origin value and enforcing host/origin checks unless 'null' is explicitly allowlisted in experimental.serverActions.allowedOrigins.

1. What is CVE-2026-27978? CVE-2026-27978 is a medium-severity cross-site request forgery (CSRF) vulnerability in next (npm), affecting versions >= 16.0.1, < 16.1.7. It is fixed in 16.1.7. A victim's authenticated browser session is used to submit forged requests to an application that cannot distinguish them from legitimate ones.
2. Which versions of next are affected by CVE-2026-27978? next (npm) versions >= 16.0.1, < 16.1.7 is affected.
3. Is there a fix for CVE-2026-27978? Yes. CVE-2026-27978 is fixed in 16.1.7. Upgrade to this version or later.
4. Is CVE-2026-27978 exploitable, and should I be worried? Whether CVE-2026-27978 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2026-27978 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2026-27978? Upgrade next to 16.1.7 or later.