On Wed, Jul 11, 2012 at 10:14 AM, Michael Felber <MichaelFelber@gmx.net> wrote:

Hi folks,

Testing impscan with zeus.vmem I have a little question about the capabilities of impscan:

Malfind finds 2 regions with injected code as seen many times:

C:\Micha\Forensics\Volatility-2.1a>python vol.py malfind -f D:\X-Ways-Images\zeus.vmem -p 1724

Volatile Systems Volatility Framework 2.1_rc1
Process: explorer.exe Pid: 1724 Address: 0x1600000

Vad Tag: VadS Protection: PAGE_EXECUTE_READWRITE
Flags: CommitCharge: 1, MemCommit: 1, PrivateMemory: 1, Protection: 6

0x01600000 b8 35 00 00 00 e9 cd d7 30 7b b8 91 00 00 00 e9   .5......0{......

…

Process: explorer.exe Pid: 1724 Address: 0x15d0000
Vad Tag: VadS Protection: PAGE_EXECUTE_READWRITE

Flags: CommitCharge: 38, MemCommit: 1, PrivateMemory: 1, Protection: 6

0x015d0000 4d 5a 90 00 03 00 00 00 04 00 00 00 ff ff 00 00   MZ..............

…

Base 0x015d0000 is a “real” exe-module and impscan can detect the hooked calls very well:

C:\Micha\Forensics\Volatility-2.1a>python vol.py impscan -f D:\X-Ways-Images\zeus.vmem -p 1724 --base 0x015d0000

Volatile Systems Volatility Framework 2.1_rc1
IAT       Call       Module               Function

---------- ---------- -------------------- --------
0x015d1000 0x77dea43c ADVAPI32.dll         CryptGetHashParam

0x015d1004 0x77dd7535 ADVAPI32.dll         RegCreateKeyExW
0x015d1008 0x77de8546 ADVAPI32.dll        CryptReleaseContext

0x015d100c 0x77dd6fc8 ADVAPI32.dll         RegQueryValueExW
0x015d1010 0x77dd778e ADVAPI32.dll         InitializeSecurityDescriptor

0x015d1014 0x77df986b ADVAPI32.dll         GetSidSubAuthorityCount
0x015d1018 0x77dd77b3 ADVAPI32.dll        SetSecurityDescriptorDacl

0x015d101c 0x77df1285 ADVAPI32.dll         SetNamedSecurityInfoW
0x015d1020 0x77dfcaf6 ADVAPI32.dll         LookupPrivilegeValueW

0x015d1024 0x77dea2f9 ADVAPI32.dll         CryptCreateHash
0x015d1028 0x77de2cde ADVAPI32.dll         ConvertStringSecurityDescriptorToSecurityDescriptorW

0x015d102c 0x77dd6a78 ADVAPI32.dll         RegOpenKeyExW
…

Base 0x01600000 contains jump instructions to other addresses:

0x1600000 b835000000       MOV EAX, 0x35
0x1600005 e9cdd7307b       JMP 0x7c90d7d7
0x160000a b891000000       MOV EAX, 0x91

0x160000f e94fdf307b       JMP 0x7c90df63
0x1600014 8bff             MOV EDI, EDI

0x1600016 55               PUSH EBP
0x1600017 8bec             MOV EBP, ESP

0x1600019 e9ef17c175       JMP 0x7721180d

So it seems to be consistent that impscan is unable to find hooked calls there:

True, as seen with vadinfo, the region at 0x01600000 ends at 0x01600fff (only 1 page):

VAD node @ 0xff38cad0 Start 0x01600000 End 0x01600fff Tag VadS

Flags: CommitCharge: 1, MemCommit: 1, PrivateMemory: 1, Protection: 6

Protection: PAGE_EXECUTE_READWRITE

If you were to disassemble all code in that region, you would not see any calls to imported functions:

>>> cc(pid = 1724)

Current context: process explorer.exe, pid=1724, ppid=1708 DTB=0x6cc0280

>>> dis(0x01600000, length = 0x1000)

0x1600000 b835000000 MOV EAX, 0x35

0x1600005 e9cdd7307b JMP 0x7c90d7d7

0x160000a b891000000 MOV EAX, 0x91

0x160000f e94fdf307b JMP 0x7c90df63

0x1600014 8bff MOV EDI, EDI

0x1600016 55 PUSH EBP

0x1600017 8bec MOV EBP, ESP

......

0x16000ce 8bff MOV EDI, EDI

0x16000d0 55 PUSH EBP

0x16000d1 8bec MOV EBP, ESP

0x16000d3 e975f64e76 JMP 0x77aef74d

0x16000d8 0000 ADD [EAX], AL

0x16000da 0000 ADD [EAX], AL

0x16000dc 0000 ADD [EAX], AL

0x16000de 0000 ADD [EAX], AL

C:\Micha\Forensics\Volatility-2.1a>python vol.py impscan -f D:\X-Ways-Images\zeus.vmem -p 1724 --base 0x01600000

Volatile Systems Volatility Framework 2.1_rc1
IAT        Call       Module               Function

---------- ---------- -------------------- --------
Traceback (most recent call last):

File "vol.py", line 185, in <module>
    main()

File "vol.py", line 176, in main
    command.execute()

File "C:\Micha\Forensics\Volatility-2.1a\volatility\commands.py", line 111, in execute
    func(outfd, data)
File "C:\Micha\Forensics\Volatility-2.1a\volatility\plugins\malware\impscan.py", line 358, in render_text

    for iat, call, mod, func in data:
File "C:\Micha\Forensics\Volatility-2.1a\volatility\plugins\malware\impscan.py", line 338, in calculate

    forward = True)
File "C:\Micha\Forensics\Volatility-2.1a\volatility\plugins\malware\impscan.py", line 130, in _vicinity_scan

    start_addr = sortedlist[0]
IndexError: list index out of range

Or does the error message mean something other?

It just means there are no calls to imported functions in the scanned memory region. However, I need to fix the IndexError. If there are no calls found, the output table should just be empty, not a backtrace.

Looked at the first jump target there is the “detoured” call as expected:

C:\Micha\Forensics\Volatility-2.1a>python vol.py impscan -f D:\X-Ways-Images\zeus.vmem -p 1724 --base 0x7c90d7d7

Volatile Systems Volatility Framework 2.1_rc1
IAT Call Module Function

---------- ---------- -------------------- --------
0x7c97d280 0x7c832b5c kernel32.dll BaseQueryModuleData

So impscan is not able to directly handle such trampoline calls, is it?

No, impscan just scans the memory region you specify with --base. It doesn't follow jumps and calls (i.e. its not an emulator).

Following the trace of the jump targets there are two imports of BaseQueryModuleData:

C:\Micha\Forensics\Volatility-2.1a>python vol.py impscan -f D:\X-Ways-Images\zeus.vmem -p 1724 --base 0x7c90df63

Volatile Systems Volatility Framework 2.1_rc1
IAT        Call       Module               Function

---------- ---------- -------------------- --------
0x7c97d280 0x7c832b5c kernel32.dll         BaseQueryModuleData

Also the next jump targets import the same api calls:

C:\Micha\Forensics\Volatility-2.1a>python vol.py impscan -f D:\X-Ways-Images\zeus.vmem -p 1724 --base 0x7721180d

Volatile Systems Volatility Framework 2.1_rc1
IAT        Call       Module               Function

---------- ---------- -------------------- --------
0x77261000 0x77dd761b ADVAPI32.dll         RegOpenKeyExA

0x77261004 0x77dfd4c9 ADVAPI32.dll         GetUserNameA
0x77261034 0x77dfc41b ADVAPI32.dll         RegOpenKeyA

…
C:\Micha\Forensics\Volatility-2.1a>python vol.py impscan -f D:\X-Ways-Images\zeus.vmem -p 1724 --base 0x771c76bd

Volatile Systems Volatility Framework 2.1_rc1
IAT        Call       Module               Function

---------- ---------- -------------------- --------
0x77261000 0x77dd761b ADVAPI32.dll         RegOpenKeyExA

0x77261004 0x77dfd4c9 ADVAPI32.dll         GetUserNameA
0x77261034 0x77dfc41b ADVAPI32.dll         RegOpenKeyA

…

I have no clue why theses api-call are hooked twice. Does anybody have an idea?

0x7721180d and 0x771c76bd are within the same VAD region, so the calls aren't being hooked twice, you're just scanning the same region twice. They are both inside 0x771b0000-0x77255fff which is where wininet.dll is loaded. So you are seeing the functions imported by wininet.dll.

VAD node @ 0xff221a68 Start 0x771b0000 End 0x77255fff Tag Vad

Flags: CommitCharge: 15, ImageMap: 1, Protection: 7

Protection: PAGE_EXECUTE_WRITECOPY

ControlArea @80f04f30 Segment e16c9008

Dereference list: Flink 00000000, Blink 00000000

NumberOfSectionReferences: 1 NumberOfPfnReferences: 78

NumberOfMappedViews: 21 NumberOfUserReferences: 22

WaitingForDeletion Event: 00000000

Control Flags: Accessed: 1, File: 1, HadUserReference: 1, Image: 1

FileObject @ff3b9130, Name: \WINDOWS\system32\wininet.dll

First prototype PTE: e16c9048 Last contiguous PTE: fffffffc

Flags2: Inherit: 1

MHL

Regards

Michael

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