In February, Cisco Managed Threat Defense (MTD) security investigators detected a rash of Dridex credential-stealing malware delivered via Microsoft Office macros. It’s effective, and the lures appear targeted at those responsible for handling purchase orders and invoices. Here’s a breakdown of the types of emails we’ve observed phishing employees and inserting trojans into user devices.
Last month, Microsoft released a security bulletin to patch CVE-2014-6332, a vulnerability within Windows Object Linking and Embedding (OLE) that could result in remote code execution if a user views a maliciously crafted web page with Microsoft Internet Explorer. Since then, there have been several documented examples of attackers leveraging this vulnerability and attempting to compromise users. On November 26th, Talos began observing and blocking an attack disguised as a hidden iframe on a compromised domain to leverage this vulnerability and compromise Internet Explorer users.
Update 7-8-14: Part 2 can be found here
This is part one in a two-part series due to the sheer amount of data we found on this threat and threat actor. This particular attack was a combined spearphishing and exploit attempt. As we’ve seen in the past, this can be a very effective combination.
In this specific example the attackers targeted a feature within Microsoft Word — Visual Basic Scripting for Applications. While basic, the Office Macro attack vector is obviously still working quite effectively. When the victim opens the Word document, an On-Open macro fires, which results in downloading an executable and launching it on the victim’s machine. This threat actor has particularly lavish tastes. This threat actor seem to target high-profile, money-rich industries such as banking, oil, television, and jewelry.
Discovering the threat
The VRT has hundreds of feeds of raw threat intelligence, ranging from suspicious URLs, files, hashes, etc. We take that intelligence data and apply selection logic to it to identify samples that are worthy of review. Using various methods from machine learning to dynamic sandbox analysis, we gather details about the samples – producing indicator of compromise (IOC), and alerts made up of multiple IOCs.
During our analysis we took the last 45 days’ worth of samples, and clustered them together based on a matching set of alert criteria. This process reduced over a million detailed sample reports to just over 15 thousand sample clusters that exhibit similar behavior. Using this pattern of similar behavior, we were capable of identifying families of malware. This led us to discover a Microsoft Word document that downloaded and executed a secondary sample, which began beaconing to a command and control server.
The Malicious Word documents & Associated Phishing campaign
The attacks we uncovered are an extremely targeted spear phish in the form of an invoice, purchase order, or receipt, written specifically for the recipient. For instance, the following is an example message we observed that purportedly came from “Maesrk”, the shipping company.
Steganography is the ancient art of invisible communication, where the goal is to hide the very fact that you are trying to hide something. It adds another layer of protection after cryptography, because encrypted message looks like gibberish and everyone immediately notices that you want to hide something. Steganography embeds the (encrypted) secret message into an innocuous looking object such that the final communication looks perfectly normal. The “analog” form of steganography is the art of writing with invisible ink. The digital version hides the message by a subtle modification of the cover object. Probably the most researched area in digital steganography uses digital images as a cover media into which the message is inserted. The oldest (and very detectable) technique replaces the least significant bit (of each colour channel) with the communicated message. Shown below, the first picture is the cover object and the second one is the stego object.