Freebox v5 HD (firmware = 1.7.20), Freebox v5 Crystal (firmware = 1.7.20), Freebox v6 Révolution r1–r3 (firmware = 4.7.x), Freebox Mini 4K (firmware = 4.7.x), and Freebox One (firmware = 4.7.x) were discovered to expose subscribers IMSI identifiers in plaintext during the initial phase of EAP-SIM authentication over the FreeWifi_secure network. During the EAP-Response/Identity exchange, the subscribers full Network Access Identifier (NAI), which embeds the raw IMSI, is transmitted without encryption, tunneling, or pseudonymization. An attacker located within Wi-Fi range (~100 meters) can passively capture these frames without requiring user interaction or elevated privileges. The disclosed IMSI enables device tracking, subscriber correlation, and long-term monitoring of user presence near any broadcasting Freebox device. The vendor acknowledged the vulnerability, and the FreeWifi_secure service is planned for full deactivation by 1 October 2025.