FreeBSD shellcode

[Joshua Davis <jdavis () transient-iss com>]

  Hi.  I developed some simple shellcode and sent it to my FreeBSD box along 
with a custom format string to exploit Qpop 2.53.  When the shellcode didn't 
work and GDB reported 'illegal instruction', I compared and contrasted.  To 
my suprise, Qpop or FreeBSD had taken the bytes 0x80, 0x88, and 0x89 from my 
shellcode.  Does anyone have any idea why this occurred?  I assume a range of 
values is being exclused.  0x79 was fine.

-- 

  Joshua Davis
  Information Security Program Operations
  Transient Infrastructure Security Solutions