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.