CVE-2026-27978

EIP tracks 1 public exploit for CVE-2026-27978. PoCs published by Nayekah.

AI-analyzed exploit summary This repository contains functional proof-of-concept exploits for three Next.js vulnerabilities, including CVE-2026-27978, which demonstrates an Origin: null bypass of Server Actions CSRF checks. Each PoC includes vulnerable and fixed environments, along with scripts to reproduce the issues.

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.