CVE-2026-53646: FOSSBilling: Client password reset token reuse allows persistent account takeover

FOSSBilling is a free, open-source billing and client management system. In versions 0.5.6 through 0.7.2, when a ClientPasswordReset record already exists for a client (from a previous unexpired reset request), subsequent calls to the resetpassword guest API endpoint reuse the existing token instead of generating a new one. The 15-minute validity window is anchored to the first request's createdat timestamp, not the time of the most recent email. An attacker who obtained the original reset link remains able to use it even after the victim requests a new reset, because the original token is never invalidated or rotated. Version 0.8.0 patches the issue. Some workarounds are available. Configure a reverse proxy (e.g., Nginx, Apache, Cloudflare) to apply per-IP rate limiting to the /client/reset-password endpoint to minimize the window of opportunity, and/or manually clear expired clientpasswordreset records from the database after a client reports a suspected compromise.