7.8 High
CVSS3
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
9.3 High
CVSS2
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
COMPLETE
Integrity Impact
COMPLETE
Availability Impact
COMPLETE
AV:N/AC:M/Au:N/C:C/I:C/A:C
0.974 High
EPSS
Percentile
99.9%
FireEye recently detected malicious Microsoft Office RTF documents that leverage CVE-2017-0199, a previously undisclosed vulnerability. This vulnerability allows a malicious actor to download and execute a Visual Basic script containing PowerShell commands when a user opens a document containing an embedded exploit. FireEye has observed Office documents exploiting CVE-2017-0199 that download and execute malware payloads from different well-known malware families.
FireEye shared the details of the vulnerability with Microsoft and has been coordinating public disclosure timed with the release of a patch by Microsoft to address the vulnerability, which can be found here.
The vulnerability bypassed most mitigations prior to patch availability; however, FireEye email and network products detected the malicious documents. FireEye recommends that Microsoft Office users apply the patch from Microsoft.
The attack occurs in the following manner:
In the two documents that FireEye observed prior to the initial blog acknowledging these attacks, malicious scripts terminated the winword.exe processes, downloaded additional payloads, and loaded decoy documents. The original winword.exe process was terminated to conceal a user prompt generated by the OLE2link. Figure 1 shows this prompt.
Figure 1: User prompt hidden by the Visual Basic script
The first malicious document identified by FireEye had three stages. An embedded OLE2 link object causes winword.exe to reach out to the following URL to download the stage one malicious HTA file:
http[:]//46.102.152[.]129/template.doc
Once downloaded, the malicious HTA file is processed by the “application/hta” handler. The highlighted line in Figure 2 shows the first download occurring, followed by the additional malicious payloads.
Figure 2: Live attack scenario
Once downloaded, the template file was stored in the user’s temporary internet files with the name template[?].hta, where [?] is determined at run time.
Mshta.exe is responsible for handling the Content-Type “application/hta,” parsing the content, and executing the script. Figure 3 shows winword.exe querying registry value of CLSID for the “application/hta” handler.
Figure 3: Winword query registry value
Winword.exe makes a request to the DCOMLaunch service, which in turn causes the svchost.exe process hosting DCOMLaunch to execute mshta.exe. Mshta.exe then executes the script embedded in the malicious HTA document. Figure 4 shows the deobfuscated VBScript from the first stage download.
Figure 4: First document, stage one VBScript
The script shown in Figure 4 performs the following malicious actions:
Once executed, the downloaded stage two VBScript (ww.vbs/maintenance.vbs) performs the following actions:
The obfuscated eoobvfwiglhiliqougukgm.js script performs the following actions when executed:
Figure 5 shows the process execution chain of events.
Figure 5: Process creation events
The final payload utilized in this malware is a newer variant of the LATENTBOT malware family. Additional details of the updates to this malware follow the Document 2 walkthrough.
MD5
|
Size
|
Name
|
Description
—|—|—|—
5ebfd13250dd0408e3de594e419f9e01
|
37,523
|
hire_form.doc
|
Malicious document
fb475f0d8c8e9bf1bc360211179d8a28
|
27,429
|
template.doc/template[?].hta
|
Malicious HTA file
984658e34e634d56423797858a711846
|
5,704
|
ww.vbs/maintenance.vbs
|
Stage two VBScript
73bf8647920eacc7cc377b3602a7ee7a
|
13,386
|
questions.doc/document.doc
|
Decoy document
11fb87888bbb4dcea4891ab856ac1c52
|
5,292
|
eoobvfwiglhiliqougukgm.js
|
Malicious script
a1faa23a3ef8cef372f5f74aed82d2de |
388,096
|
wood.exe/ dcihprianeeyirdeuceulx.exe
|
Final payload
15e51cdbd938545c9af47806984b1667
|
414,720
|
wood.exe/ dcihprianeeyirdeuceulx.exe
|
Updated final payload
Table 1: First document file metadata
The payload associated with the first document is an updated version of the LATENTBOT malware family. LATENTBOT is a highly-obfuscated BOT that has been in the wild since 2013.
The newer version of the LATENTBOT has different injection mechanisms for Windows XP (x86) and Windows 7 operating systems:
In Windows 7 or later operating systems, the bot does not use attrib.exe. Rather, it injects code into svchost.exe followed by launching the default browser with malicious payload by leveraging NtMapViewOfSection().
This variant then connects to the following command and control (C2) server:
Upon successful communication with the C2 server, LATENTBOT generates a beacon. One of the decrypted beacons are as follows with an updated version number of 5015:
At the time of analysis, the C2 server was offline. The bot comes with a highly modular plugin architecture and has been associated with the “Pony” campaigns as an infostealer.
As of April 10, 2017, the malware hosted at www.modani[.]com/media/wysiwyg/wood.exe has been updated and the C2 server has been moved to: 217.12.203[.]100.
The second malicious document identified by FireEye consisted of two malicious stages. The initial stage reached out to the following URL to download the stage one malicious HTA file:
http[:]//95.141.38[.]110/mo/dnr/tmp/template.doc
This file is downloaded into the user’s temporary internet files directory with the name template[?].hta, where [?] is determined at runtime. Once downloaded, winword.exe utilizes mshta.exe to parse the file. mshta.exe parses through file finding <script> </script> tags and executes the contained script. Figure 6 shows the deobfuscated script.
Figure 6: Second document, first stage VBScript
Figure 6 shows the following malicious actions:
Examination of the malicious payload revealed that it is a variant of the dropper for what Microsoft calls WingBird, which has similar characteristics as FinFisher. The malware is heavily obfuscated with several anti-analysis measures, including a custom VM to slow analysis. A blog post by “Artem” covers a payload driver of WingBird. The blog author briefly mentions the protection techniques of the dropper, which match this sample.
MD5
|
Size
|
Name
|
Description
—|—|—|—
c10dabb05a38edd8a9a0ddda1c9af10e
|
70,269
|
СПУТНИК РАЗВЕДЧИКА.doc
|
Malicious document
9dec125f006f787a3f8ad464d480eed1
|
27,500
|
template.doc
|
Malicious HTA file
acde6fb59ed431000107c8e8ca1b7266
|
1,312,768
|
copy.jpg/winword.exe
|
Final payload
e01982913fbc22188b83f5f9fadc1c17
|
6,220,783
|
docu.doc/document.doc
|
Decoy document
Table 2: Second document metadata
FireEye observed CVE-2017-0199, a vulnerability in Microsoft Word that allows an attacker to execute a malicious Visual Basic script. The CVE-2017-0199 vulnerability is a logic bug and bypasses most mitigations. Upon execution of the malicious script, it downloads and executes malicious payloads, as well as displays decoy documents to the user. The two documents achieve execution of their malicious payloads, with one containing LATENTBOT and the other containing WingBird/FinFisher. The malicious document contained only a link to the attacker controlled server, showing the advantage of FireEye’s MVX engine to detect multi-stage attacks. Further campaigns leveraging this attack have been observed prior to patch availability, but are not covered in this blog.
We recommend that Microsoft Office users apply the patch as soon as possible.
Thank you to Michael Matonis, Dhanesh Kizhakkinan, Yogesh Londhe, Swapnil Patil, Joshua Triplett, and Tyler Dean from FLARE Team, FireEye Labs Team, and FireEye iSIGHT Intelligence for their contributions to this blog. Thank you as well to everyone who worked with us at the Microsoft Security Response Center (MSRC).
7.8 High
CVSS3
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
REQUIRED
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
9.3 High
CVSS2
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
COMPLETE
Integrity Impact
COMPLETE
Availability Impact
COMPLETE
AV:N/AC:M/Au:N/C:C/I:C/A:C
0.974 High
EPSS
Percentile
99.9%