Last October different law enforcement agencies orchestrated a takedown of the Dridex Botnet. However, the threat actors behind Dridex spam runs seem stronger than ever. The resurrection of Dridex after the announced take down has been ferocious. During the last Black Friday in our spam traps we observed at least four different phishing campaigns delivering Dridex. Each campaign was carefully crafted in order to lure the users to open the malicious documents. The creativity of the threat actors is captivating. The below picture illustrates one of these emails that is supposedly sent from the well-known rent-a-car company AVIS. The email contains a Microsoft Office document attached that contains malicious macros on it.
Another one was an email supposedly sent from Bruce Sharpe from the Industrial Pump Supplier Aline Pumps in Australia. According to the social network zoominfo Bruce Sharpe exists and is an account manager in the company. The subject was Tax Invoice and once again the email contained a Microsoft Office document attached with malicious macros.Other one was an email sent from Ivan Jarman from SportSafe UK. The company is a global provider of sports equipment. This time the subject was Invoice and the email contained a Microsoft Office document attached with malicious macros. The last one was an email from the company Integrated Petroleum Services. According to the website one key location is Equatorial Guinea and the emails supposedly come from there. The subject this time was Transfer and the email contained a Microsoft Office document attached with malicious macros. As bonus the footer will mention the email has been scanned by the Antivirus AVAST. All documents use the same technique. Attract the user to enable macros in order to view the document contents.
Across all the campaigns the technique is the same. All the Microsoft Office documents contain embedded macros that download a malicious executable from one of many hard coded URLs. These hard coded URLs are normally collateral victims of the operation. The encoding and obfuscation techniques used in the macros are constantly changing in order to bypass security controls.
Normally these URLs are hosted under legitimate sites that have been compromised to host the malicious file. When the macro is executed it will fetch a second stage payload from the compromised server. This payload is then saved to C:\Users\%%username\AppData\Local\Temp and then executed.
After the machine gets infected Dridex will start beaconing out to the C2 addresses. Dridex uses HTTP to encapsulate the traffic and encrypts the payload. Below an example how the first HTTP POST request made by the infected machine looks like in the network. A POST to the root folder full of gibberish.
From this moment onward the malware is capable of stealing all kinds of credentials from the victim’s computer. It can also redirect victim’s traffic to sites controlled by the threat actors using man-in-the-browser functionality. This allows interception and manipulation of traffic that is supposed to be delivered to legitimate sites. Dridex has remote access functionality that allows the threat actor to connect to websites trough the victim computer.
Phishing campaigns that distribute commodity malware are common and ongoing problem for end users and corporations.E-mail continues to be the weapon of choice for mass delivering malware. The tools and techniques used by attackers continue to evolve and bypass all the security controls in place. From a defense perspective, the US-CERT put together excellent tips for detecting and preventing this type of malware and to avoid scams and phishing attempts applicable to home users and corporations.