Bank Malspam Revisited

Last week we wrote about some malicious spam containing Microsoft Publisher files, leading to the FlawedAmmyy RAT, where the actors behind the campaign were targeting banks.

The same actors have resumed business today, however this time, they embedded the Publisher files within a PDF document. Again, all the target domains were banks.

Below is a representation of how the Trustwave Secure Email Gateway unpacks the message, you can see the Publisher file within the PDF. The ultimate payload was still FlawedAmmyy, so same trick, different package.

21 August – PDF with embossed .pub file – Subject: PDF_2108 or Subject: Payment Notification

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Embedding stuff within a PDF is a favorite trick with this group, which uses the Necurs botnet to distribute its malware. See here and here for previous examples.

We also got curious as to what other attachments this group may be spamming out, so we went back further and studied the historical data more carefully. What we saw was a range of attachments being spammed, again targeting banks, and reaching back as far as 10 August at least. We didn't pick up on these earlier as the gateway was blocking all these samples (as it should). Here are some samples:

10 August – Doc with Macro – Subject: Invoice 7616

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14 & 15 August – IQY file embedded in a PDF – Subject: MIS 93807.15/08/2018 or Subject: dhfl

3

21 August – IQY File – Subject: Sua NF-e foi emitida n° ( 670806)

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21 August – Pub file – Subject: confirmation

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What all this shows is the actors trying their usual array of tricks and file formats, but in different combinations and different packages. And, of course, determined in their widespread targeting of banks.

Banks and, well everyone, should consider blocking IQY files at the email gateway, and closely inspect inbound document files for other suspect embedded files and macros.

For Trustwave Secure Email Gateway customers, the gateway is detecting all the samples seen to date.

IOCs

PDF Files

MD5: 65713d26cf111eb64de1aa524bbecb2b
SHA1: e1f1b2dcf933f5f5fc9957f1d8dd79c3d51ba5cf

MD5: 96df741e40070e964f7bd08bb055015f
SHA1: 8ab68980410395ade6d239c3f4414a52bff39926

Embedded PUB file

MD5: 2cbfcd096e7ba69d528487d5351451e5
SHA1: 6b18a10f4ced27eb8bd18a2b0e441a344296392b

File from URL(hxxp://g78k[.]com/set)

MD5: 0906ab6a9ed0fa8f173d6800f8957f4a
SHA1: 6c8bb389db9c4a8b4228c7f9143ae7731c5a72a9

Unpacked file (FlawedAmmyy RAT)

MD5: 73964f92d3e5e142047574afa78726e3
SHA1: c8d84d0c6894fd2b640a2b699c03ecb042c3ebfc

DOC file with Macro

MD5: bb4dd09e221c17b5878c1996499bbd70
SHA1: 1c4caf598f75b292d0f97dbb39be580e4766c637

PDF with embedded IQY file

MD5: 839e9a3ecec7e8f735875ec65f1466e0
SHA1: 39c007372d262ed7bd9391ff89986b54e060244f

IQY file

MD5: 8347243399a4880ec456661edffe2613
SHA1: 471235ef3411ab474c0481a0527ae8c78e4ca6a6

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