The FWDOWNL firmware-download implementation in Asterisk Open Source 1.0.x 1.2.x before 1.2.30 and 1.4.x before 1.4.21.2; Business Edition A.x.x B.x.x before B.2.5.4 and C.x.x before C.1.10.3; AsteriskNOW; Appliance Developer Kit 0.x.x; and s800i 1.0.x before 1.2.0.1 allows remote attackers to cause a denial of service (traffic amplification) via an IAX2 FWDOWNL request.