Cyber Crime

Unusual Malspam campaign targets banks with Microsoft Publisher files

Researchers from Trustwave have uncovered a malspam campaign targeting banks with the FlawedAmmyy RAT.

The peculiarity of this malspam campaign is the unusual use of a Microsoft Office Publisher file to infect victims’ systems.

Experts noticed an anomalous spike in the number of emails with a Microsoft Office Publisher file (a .pub attachment) and the subject line, “Payment Advice,” that was sent to domains belonging to banks.

This campaign is very small but appears to be very focused on banks.

The spam messages contained URLs that downloaded FlawedAmmyy remote-access trojan (RAT), a well-known backdoor.

Another interesting aspect of the campaign is that It was powered by the Necurs botnet.

“This campaign was unusual in the use of .pub files. It also appeared to originate from the Necurs botnet, a notorious botnet responsible for much mass malware distribution in the past,” reads the analysis published by Trustwave.

“Unlike previous mass campaigns, this campaign was small and, interestingly, all of the To: addresses we saw targeted were domains belonging to banks, indicating a desire for the attackers to get a foothold within banks with the FlawedAmmyy RAT.”

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When the victims open the pub file, they are prompted to “Enable Macros,” earlier versions of Microsoft Publisher may display instructions to “Enable Editing” and “Enable Content”

When manually opening the Visual Basic Editor (VBA Editor) in Microsoft Publisher and clicking “ThisDocument” in Project Explorer, the VBScript executes a weaponized archive containing the RAT.

“The macro script is triggered with the function Document_Open(). As the name implies, when the file is opened, the script will access a URL and execute a downloaded file.” continues the analysis.

The malicious code leverages control objects in forms to hide the URL from which It downloads the RAT, the URL is stored in the Tag Property.

“By the time we examined the sample, the URL was not accessible anymore, but a little further research indicated this URL was used for downloading a self-extracting archive, which contained the FlawedAmmyy RAT,” researchers said.

In July, Proofpoint uncovered another massive malspam campaign delivering the FlawedAmmyy RAT that was leveraging emails with weaponized PDF documents containing malicious SettingContent-ms files.

The campaign was attributed to the financially motivated cybercriminal group TA505.

“this campaign was unusual in the use of .pub files. It also appeared to originate from the Necurs botnet, a notorious botnet responsible for much mass malware distribution in the past (see here and here).” concludes Trustwave.

“Unlike previous mass campaigns, this campaign was small and, interestingly, all of the To: addresses we saw targeted were domains belonging to banks, indicating a desire for the attackers to get a foothold within banks with the FlawedAmmyy RAT.” 

Technical details, including the IoCs, are reported in the analysis published by the experts.

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Pierluigi Paganini

(Security Affairs – Malspam, Publisher)

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Pierluigi Paganini

Pierluigi Paganini is member of the ENISA (European Union Agency for Network and Information Security) Threat Landscape Stakeholder Group and Cyber G7 Group, he is also a Security Evangelist, Security Analyst and Freelance Writer. Editor-in-Chief at "Cyber Defense Magazine", Pierluigi is a cyber security expert with over 20 years experience in the field, he is Certified Ethical Hacker at EC Council in London. The passion for writing and a strong belief that security is founded on sharing and awareness led Pierluigi to find the security blog "Security Affairs" recently named a Top National Security Resource for US. Pierluigi is a member of the "The Hacker News" team and he is a writer for some major publications in the field such as Cyber War Zone, ICTTF, Infosec Island, Infosec Institute, The Hacker News Magazine and for many other Security magazines. Author of the Books "The Deep Dark Web" and “Digital Virtual Currency and Bitcoin”.

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