GHSA-mq59-m269-xvcx

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.