CVE-2026-27978: Next.js: null origin can bypass Server Actions CSRF checks

In plain English

A medium-severity cross-site request forgery in next.js from vercel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 12% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.

Official 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, `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.

Ecosystem	Package	Fixed in	Advisory
npm	next	16.1.7	GHSA-mq59-m269-xvcx

Ecosystem

Package

Fixed in

Advisory

npm

16.1.7

GHSA-mq59-m269-xvcx

Vendor	Product	Versions
vercel	next.js	>= 16.0.1, < 16.1.7

Vendor

Product

Versions

vercel

next.js

>= 16.0.1, < 16.1.7

CVE-2026-27978Next.js: null origin can bypass Server Actions CSRF checks

In plain English

Official description

Affected packages & fixed versions

Affected products (as reported)

References