Unspecified vulnerability in Cisco IOS 12.0 through 12.4, when configured with (1) IP Service Level Agreements (SLAs) Responder, (2) Session Initiation Protocol (SIP), (3) H.323 Annex E Call Signaling Transport, or (4) Media Gateway Control Protocol (MGCP) allows remote attackers to cause a denial of service (blocked input queue on the inbound interface) via a crafted UDP packet.