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Sophos has published a technical deep dive into Qakbot, explaining how the botnet is becoming more advanced and dangerous to organisations.
In a new article, “Qakbot Injects Itself into the Middle of Your Conversations”, Sophos researchers detail a recent Qakbot campaign that shows how the botnet spreads through email thread hijacking and collects a wide range of profile information from newly infected machines, including all the configured user accounts and permissions, installed software, running services and more. The botnet then downloads a series of additional malicious modules that enhance the functionality of the core botnet, according to Sophos.
Qakbot’s malware code features unconventional encryption, which it also uses to conceal the content of its communications.
According to Sophos, it decrypted the malicious modules and decoded the botnet’s command and control system to interpret how Qakbot receives instructions.
Qakbot is a modular, multipurpose botnet spread by email that has become increasingly popular with attackers as a malware delivery network, like Trickbot and Emotet, Andrew Brandt, principal threat researcher at Sophos further explained.
“Sophos’ deep analysis of Qakbot reveals the capture of detailed victim profile data, the botnet’s ability to process complex sequences of commands and a series of payloads to extend the functionality of the core botnet engine.
“The days of thinking of ‘commodity’ bots as merely annoying are long gone.”
Brandt added that security teams need to take the presence of Qakbot infections on their network seriously and investigate and remove every trace because botnet infections are a known precursor for a ransomware attack.
“This is not simply because botnets can deliver ransomware, but because botnet developers sell or lease their access to breached networks.
“For example, Sophos has encountered Qakbot samples that deliver Cobalt Strike beacons directly to an infected host.
“Once the Qakbot operators have used the infected computer they can transfer, lease out or sell access to these beacons to paying customers,” Brandt said.
The Qakbot infection chain and payloads
In the campaign Sophos analysed, the Qakbot botnet inserted malicious messages into existing email conversations.
The inserted emails include a short sentence and a link to download a zip file containing a malicious Excel spreadsheet. The user was asked to “enable content” to activate the infection chain.
Once the botnet had infected a new target, it performed a detailed profile scan, sharing the data with its command-and-control server and then downloading additional malicious modules.
The Qakbot botnet downloaded at least three different malicious payloads in the form of dynamic link libraries (DLL). According to Sophos, these DLL payloads provide the botnet with a wider range of capabilities.
The payloads were injected into browsers and contained the following:
Security advice
Sophos researchers recommend that users approach unusual or unexpected emails with caution, even when the messages appear to be replies to existing email threads.
In the Qakbot campaign investigated by Sophos, a potential red flag for recipients was the use of Latin phrases in URLs.
Security teams should check that the behavioural protections provided by their security technologies prevent Qakbot infections from taking hold according to Sophos researchers. Network devices will also alert administrators if an infected user attempts to connect to a known command-and-control address or domain.
[Related: Cyber criminals and nation-state actors reportedly converging and collaborating]
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