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Showing posts from 2017

Signature Dev using for RTF zero day CVE-2017-8759

After reading the FireEye blog on CVE-2017-8759 we decided to quickly write a signature for the new (though not yet widely used, and now patched) zero day. We decided to use, naturally.

First we searched for the FireEye reported hash fe5c4d6bb78e170abf5cf3741868ea4c in

The first hex block looks interesting:
Clicking the sha256 link brings up the hex view, it's a OLE document embedded in the RTF. We can see a wsdl link and the highlighted hex turns out to be part of the class id, rendered as c7b0abec-197f-d211-978e-0000f8757e2a. Reversing the first three block's byte order comes out to the SoapMoniker class ID ECABB0C7-7F19-11D2-978E-0000F8757E2A

This handy list reveals the SoapMoniker class:

After some testing, we pushed out a CVE-2017-8759 signature to and the free open source version.

EPS obfuscation for MS Office exploits

We took a deeper look into a recent FireEye blog post on 2 new EPS exploits used while zero-day by the APT 28 / Turla group.  Both exploits have been patched. One of the samples used an interesting EPS based obfuscation technique to avoid detection. By using a 4 byte xor within native Postscript commands the exploit code can be obfuscated and decoded in memory at run time defeating static analysis.

CVE-2017-0262 Sample Report

The obfuscation The PostScript code starts with a xor loop using key 0xC45D6491 using only built-in PostScript functionality

Using our Cryptam multi tool, we'll decode the EPS block manually:
$ php cryptam_multi.php eps.test -xor c45d6491 using XOR key c45d6491

$ ./quicksand.out eps.test.out  -0> root {7}   md5:237e6dcbc6af50ef5f5211818522c463   sha1:228c21dff49376c0946fe2bbe21448bbdbfcf13a   sha256:385655e10c8a7718bb50e969979cf4f08a2380f67827ce01d05874c49b3a5c13   head:7b202f48656c7665   size:347320   yara:exploits:exploit_cve_2017_0262   yara:executable…

Office 0day goes mainstream

CVE-2017-0199 MS Office Exploit

On Friday April 7, 2017, McAfee posted that a new Office zero day affecting even the most recent versions of Windows and Office was found in the wild, FireEye released a blog post the next day confirming the zero day.

Using details from the 2 posts we were able to find 5 samples from the targeted attacks which use the "htmlfile" class ID 25336920-03f9-11cf-8fd0-00AA00686f13 to load remote content with trusted permissions.   The remote content which appears to be a RTF file with an embedded HTML-style [script language="VBScript"] exploit to download and run a remote executable using powershell.

More concerning, is the emergence of a mass-emailed campaign today (April 10, 2017). Malware Tracker discovered a large campaign using the exploit and common "Scan Data" themed emails. The emails contain a randomly named nnnnnnnn[1].doc rtf file which uses the zero day exploit in a barely modified form. We have observed 2 samples - a …