Asterisk Project Security Advisory – On certain implementations of libc, the scanf family of functions uses an unbounded amount of stack memory to repeatedly allocate string buffers prior to conversion to the target type. Coupled with Asterisk’s allocation of thread stack sizes that are smaller than the default, an attacker may exhaust stack memory in the SIP stack network thread by presenting excessively long numeric strings in various fields.
You can download this advisory from the following link: https://packetstormsecurity.com/files/download/80271/AST-2009-005.txt
Source: https://packetstormsecurity.com/files/80271/Asterisk-Project-Security-Advisory-Driver-Crash.html