CVE-2026-63439: 2FAuth: Reverse Proxy Guard Trusts Client-Supplied Headers Without Proxy Verification

2FAuth is a web app to manage Two-Factor Authentication (2FA) accounts and generate their security codes. Prior to 8.0.0, when AUTHENTICATIONGUARD=reverse-proxy-guard is enabled, ReverseProxyGuard::user() reads the default REMOTEUSER identity header, or a custom identity header selected by the AUTHPROXYHEADERFORUSER configuration setting, without confirming that the request originated from a configured trusted proxy. A remote client that can reach the application directly can forge the selected identity header and authenticate as an existing user, including an administrator, gaining access to stored 2FA secrets and account or application management functions. This issue is fixed in version 8.0.0.