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Random Malware Analysis

2009/05/22

Having recently been left with several hours to kill with nothing but a laptop and my virtual lab I thought I’d try my hand at some rudimentary malware analysis. For a random live sample I selected the most recent submission to my Nepenthes Server.

$ tail -n1 /opt/nepenthes/var/log/logged_submissions
[2009-05-21T19:10:59] 90.130.169.175 -> 195.97.252.143 creceive://90.130.169.175:2526 93715cfc2fbb07c0482c51e02809b937

To start with I wanted to get an idea of what I was dealing with, so I passed the file’s hash to VirusTotal’s Hash Search utility; and promptly found that VirusTotal had no knowledge of this particular hash. Means we could be dealing with a completely new malware strain or variant! or more likely a polymorphic binary creating a unique file signature…

The question was promptly answered when transferring the binary to my analysis machine by AVG, ‘Threat detected: worm/Allaple.b’. Not wanting to take the word of a single AV vendor I proceeded to upload the binary itself to VirusTotal (have I mentioned I like VirusTotal yet?). Sure enough most AV engines agree with AVG’s analysis although there was some dissention over which version of Allaple the sample was. Most AV engines (37/40) flagged file as malicious (Comodo, nProtect and PrevX gave the binary a clean bill of health.)

Beginning with some static analysis, the ‘strings’ utility is always a safe place to start. As I’m using a Windows platform for this analysis I use the SysInternals strings binary. This revealed little, other than confirming the binary is a windows executable (usual ‘!This program cannot be run in DOS mode.’ string) and a reference to Kernal32.dll and some function names (FindFirstVolumeW, GetShortPathNameA, GetConsoleAliasesLengthW, AddConsoleAliasA, GetModuleHandleW, CreateProcessA, GetUserDefaultUILanguage, LocalReAlloc, SetHandleInformation, SetConsoleCursorInfo).

As there was limited information available from a plaintext strings search my next step was to see if the binary had been packed. For this I used PEiD utility, PEiD initially stated that there was ‘Nothing Detected’ although the entropy found within the file (7.93) caused PEiD to suggest that the binary had indeed been packed.

With some basic static analysis undertaken (this could/should have been taken further but my RE/assembly-fu is a bit rusty, especially at 3am) I changed tact and went with some initial behavioural analysis. For an initial run I utilised iDefense’s SysAnalzer tool written by David Zimmer. SysAnalyzer is a great utility for automating behavioural analysis and capturing system changes, from it’s download page:

SysAnalyzer is an automated malcode run time analysis application that monitors various aspects of system and process states.
SysAnalyzer was designed to enable analysts to quickly build a comprehensive report as to the actions a binary takes on a system.

The tool snapshots (not to be confused with VM snapshots) the state of the system, runs a given binary, then snapshots the system after execution before comparing the two snapshots. This can provide some detailed, succinct information to an analyst, but may miss any dynamic and temporary system changes. One weakness (or strength, depending on your perspective) that SysAnalyzer has is that it does not sandbox the malicious binary from the analysis system. Meaning that if the binary is destructive it *will* hose the system it is being analysed on, obviously if you’re utilising virtualisation and snapshop functionality this shouldn’t be an issue.

On starting the analysis, the malicious executable promptly errored (usual Windows’ ‘executable has failed, please send all information to Microsoft’ type pop-up) and SysAnalysis stated that the system was unchanged by the binary. Well that was disappointing, possible some form of VM detection causing the malware to shut down?

Not to be denied, I re-ran the process: Again the executable crashed with Microsoft’s pop-up, but this time SysAnalysis saw some system changes, from API and registry calls to the creation of new processes. However on further analysis the new processes and files were all only related to the DWWIN.exe executable which, as explained here, is part of Windows itself and is the cause of the pop-ups discussed above.

One aspect that may be causing the binary to lock up is that it is isolated from the network. From experience some malware will perform an initial lookup to an external resource, if the code can’t access said resource the malware assumes it is on a closed system and shuts down. To test this theory I re-ran the executable (this time manually, without the SysAnalysis utility) with Wireshark sniffing all network interfaces. As expected the binary crashed with the same error pop-up, reviewing the wireshark capture no traffic was generated outbound to any resource from the infected host.

Another possible reason for malware to refuse to run is newer VM detection techniques. However no evidence of this is present in the API calls captured by SysAnalysis, nor can I find any reference to VM detection capabilities present within the Allaple family from a search of the web. Ideally to test this theory the malware would be executed on a natively installed OS to bypass any potential VM detection. Unfortunately at this stage I do not have resources available to sacrifice a physical machine in this manner, so analysis must stop here.

One final possibility is simply that the binary is defective, just because the malware is spreading does not necessarily mean that the payload delivered upon exploitation is fully functional. It is not uncommon to have one malware strain being propogated by an entirely different strain. This is rapidly becoming more prevelant as ‘cybercrime’ (I hate that phrase) matures with the recent emergence of crimeware-as-a-service.

What-ever the reason for the binary failing to have any perceivable impact on the system, the behaviour that has been observed during this sample’s execution does not match that which is expected from other analysis of the Allaple.b malware strain. Sophos’ analysis for example, states that upon infection Allabple.b will:

  • When first run W32/Allaple-B copies itself to [system]\urdvxc.exe.
  • The W32/Allaple-B is registered as a COM object.
  • W32/Allaple-B installs itself as a service with the name “MSWindows”.

No evidence of this behaviour has been seen during analysis, nor are any of the changes present on the system post infection. This is a good example of why there isn’t always a need to panic when AV picks up a malicious item. Until the infection has been analysed in more depth there is no way of knowing how scary the compromise and infection is.

Andrew Waite

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  1. 2010/05/24 at 22:57

    I’ve seen hackers drop defective or partially functioning malware as decoys/detractors to send forensic teams on a wild goose chase while the hacker is busy doing other things. It’s probably not the case in the above situation, but I thought I would mention it.

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