Packed Code

Packed Code is frequent ingredient of armored malware. Here we demonstrate a few WinDbg commands to detect UPX packed modules with little or no expected strings:

0:000> !dh 00000000`00fd40b0


File Type: DLL
FILE HEADER VALUES
14C machine (i386)
3 number of sections
time date stamp Fri Jan 18 21:27:25 2013


0 file pointer to symbol table
0 number of symbols
E0 size of optional header
2102 characteristics
Executable
32 bit word machine
DLL

OPTIONAL HEADER VALUES
10B magic #
11.00 linker version
6000 size of code
1000 size of initialized data
F000 size of uninitialized data
15600 address of entry point
10000 base of code
----- new -----
0000000010000000 image base
1000 section alignment
200 file alignment
2 subsystem (Windows GUI)
6.00 operating system version
0.00 image version
6.00 subsystem version
17000 size of image
1000 size of headers
0 checksum
0000000000100000 size of stack reserve
0000000000001000 size of stack commit
0000000000100000 size of heap reserve
0000000000001000 size of heap commit
140  DLL characteristics
Dynamic base
NX compatible
16274 [       AC] address [size] of Export Directory
161DC [       98] address [size] of Import Directory
16000 [     1DC] address [size] of Resource Directory
0 [       0] address [size] of Exception Directory

0 [       0] address [size] of Security Directory
16320 [      10] address [size] of Base Relocation Directory
0 [       0] address [size] of Debug Directory
0 [       0] address [size] of Description Directory
0 [       0] address [size] of Special Directory
0 [       0] address [size] of Thread Storage Directory
157CC [      48] address [size] of Load Configuration Directory
0 [       0] address [size] of Bound Import Directory
0 [       0] address [size] of Import Address Table Directory
0 [       0] address [size] of Delay Import Directory
0 [       0] address [size] of COR20 Header Directory
0 [       0] address [size] of Reserved Directory

SECTION HEADER #1
UPX0 name
F000 virtual size
1000 virtual address
0 size of raw data
400 file pointer to raw data
0 file pointer to relocation table
0 file pointer to line numbers
0 number of relocations
0 number of line numbers
E0000080 flags
Uninitialized Data
(no align specified)
Execute Read Write

SECTION HEADER #2
UPX1 name
6000 virtual size
10000 virtual address
5A00 size of raw data
400 file pointer to raw data
0 file pointer to relocation table
0 file pointer to line numbers
0 number of relocations
0 number of line numbers
E0000040 flags
Initialized Data
(no align specified)
Execute Read Write

SECTION HEADER #3
.rsrc name
1000 virtual size
16000 virtual address
400 size of raw data
5E00 file pointer to raw data
0 file pointer to relocation table
0 file pointer to line numbers
0 number of relocations
0 number of line numbers

C0000040 flags
Initialized Data
(no align specified)
Read Write

0:000> s-sa 00000000`00fd40b0 L6600
00000000`00fd40fd  "!This program cannot be run in D"
00000000`00fd411d  "OS mode."
00000000`00fd4188  "Rich"
00000000`00fd4290  "UPX0"
00000000`00fd42b8  "UPX1"
00000000`00fd42e0  ".rsrc"
00000000`00fd448b  "3.08"
00000000`00fd4490  "UPX! "
00000000`00fd449b  "YhHM4"
00000000`00fd44d1  "vqx"
[...]

Such in-memory modules (not yet initialized by a loader) can be saved to disk using .writemem command and unpacked. Once loaded and relocated into some address they still have UPX sections but they now have more strings:

0:000> s-sa 00000000`691c0000 L300
00000000`691c004d  "!This program cannot be run in D"
00000000`691c006d  "OS mode."
00000000`691c00d8  "Rich"
00000000`691c01e0  "UPX0"
00000000`691c0207  "`UPX1"
00000000`691c022f  "`.rsrc"
[...]
00000000`691d620b  "uGC"
00000000`691d621c  "KERNEL32.DLL"
00000000`691d622a  "LoadLibraryA"
00000000`691d6238  "GetProcAddress"
00000000`691d6248  "VirtualProtect"
00000000`691d6258  "VirtualAlloc"
00000000`691d6266  "VirtualFree"
[...]

0:000> s-su 00000000`691c0000 L(00000000`691d7000-00000000`691c0000)
[...]
00000000`691c8178  “http://www.patterndiagnostics.com”
00000000`691c8260  “mscoree.dll”
[...]