A flaw was found in freeradius's EAP-FAST module. The SessionTicket callback invoked during the TLS ClientHello phase of the EAP-FAST handshake validates the PAC-Opaque length using mismatched integer types, allowing an attacker-supplied value to underflow and bypass the check. The callback then decrypts attacker-controlled ciphertext into a fixed-size buffer before the authentication tag is verified, so a crafted ClientHello can write data past the end of a stack buffer. A remote, unauthenticated client speaking EAP-FAST to a server with the module enabled can trigger this to crash the RADIUS server process before any credential exchange.