A previously unseen malware variant, dubbed the Cannon Trojan, is being used in targeted attacks on government agencies in the United States and Europe. The new malware threat has been strongly linked to a threat group known under many names – APT28, Fancy Bear, Sofacy, Sednet, Strontium – that has links to the Russian government.
The Cannon Trojan is being used to gather information on potential targets, collecting system information and taking screenshots that are sent back to APT28. The Cannon Trojan is also a downloader capable of installing further malware variants onto a compromised system.
The new malware threat is stealthy and uses a variety of tricks to avoid detection and hide communications with its C2. Rather than communicating over HTTP/HTTPS, like other malware variants used by APT28, the Cannon Trojan communicates via email over SMTPs and POP3S.
Once installed, an email is sent over SMTPS through port 465 and a further two email addresses are obtained through which the malware communicates with its C2 using the POP3S protocol to receive instructions and send back data. While the use of email for communicating with a C2 is not unknown, it is relatively rare. One advantage offered by this method of communication is it is more difficult to identify and block that HTTP/HTTPS.
The Cannon Trojan, like the Zebrocy Trojan which is also being used by APT28, is being distributed via spear phishing emails. Two email templates have been intercepted by Palo Alto Networks’ Unit 42 team, one of which takes advantage of interest in the Lion Air plane crash in Indonesia.
The Lion Air spear phishing campaign appears to provide information on the victims of the crash, which the email claims are detailed in an attached Word document titled Crash List (Lion Air Boeing 737).docx. The user must Enable Content to view the contents of the document. It is claimed that the document was created in an earlier version of Word and content must be enabled for the file to be displayed. Opening the email and enabling content would trigger the macro to run, which would then silently download the Cannon Trojan.
Rather than the macro running and downloading the payload straightaway, as an anti-analysis mechanism, the attackers use the Windows AutoClose tool to delay completion of the macro routine until the document is closed. Only then is the Trojan downloaded. Any sandbox that analyzes the document and exits before closing the document would be unlikely to identify it as malicious. Further, the macro will only run if a connection with the C2 is established. Even if the document is opened and content is enabled, the macro will not run without its C2 channel open.
The techniques used by the attackers to obfuscate the macro and hide communications make this threat difficult to detect. The key to preventing infection is blocking the threat at source and preventing it from reaching inboxes. The provision of end user training to help employees identify threats such as emails with attachments from unknown senders is also important.
Enhance Protection Against Zero-Day Malware and Spear Phishing
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Greylisting is used to identify domains used for spamming that have yet to be blacklisted. All incoming emails are subjected to Bayesian analysis, and heuristics are used to identify new threats.
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