2Apr-20

SLAE – Assignment #7: Custom Shellcode Crypter

Assignment #7: Custom Shellcode Crypter

Seventh and last SLAE’s assignment requires to create a custom shellcode crypter. Since I had to implement an entire encryption schema both in python as an helper and in assembly as the main decryption routine, I've opted for something simple. I've chosen the Tiny Encryption Algorithm (TEA) as it does not require large IV or SBOX initialization vectors (adding a huge overhead to my shellcode's decoding routine), because it's tiny and not too...
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2Apr-20

SLAE – Assignment #6: Polymorphic Shellcode

Assignment #6: Polymorphic Shellcode

Sixth SLAE’s assignment requires to create three different (polymorphic) shellcodes version starting from published Shell Storm's examples. I've decided to take this three in exam: http://shell-storm.org/shellcode/files/shellcode-752.php - linux/x86 execve ("/bin/sh") - 21 bytes http://shell-storm.org/shellcode/files/shellcode-624.php - linux/x86 setuid(0) + chmod("/etc/shadow",0666) - 37 bytes http://shell-storm.org/shellcode/files/shellcode-231.php - linux/x86 open cd-rom loop (follows "/dev/cdrom" symlink) - 39 bytes As always, all the code is also available on GitHub. Stay updated, join...
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26Mar-20

SLAE – Assignment #5: Metasploit Shellcode Analysis

Assignment #5: Metasploit Shellcode Analysis

Fifth SLAE’s assignment requires to dissect and analyse three different Linux x86 Metasploit Payload. Metasploit currently has 35 different payloads but almost half of it are Meterpreter version, thus meaning staged payloads. I’ve then decided to skip meterpreter payloads as they involve multiple stages and higher complexity that will break libemu graph generation (which I find very useful to better explain shellcode’s operations). In this blog we are going to analyse the following shellcodes: linux/x86/shell_find_tag linux/x86/shell_find_port linux/x86/shell/bind_nonx_tcp As always,...
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17Mar-20

SLAE – Assignment #4: Custom shellcode encoder

Assignment #4: Custom Shellcode Encoder

As the 4th SLAE’s assignment I was required to build a custom shellcode encoder for the execve payload, which I did, here how. Stay updated, join VoidSec's Telegram Channel: https://t.me/voidsec_updates

Encoder Implementations

I’ve decided to not relay on XORing functionalities as most antivirus solutions are now well aware of this encoding schema, the same reason for which I’ve skipped ROT13 and other “rotating” encoding. I thought of using some multiple weird shifting schema but that...
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