Malspam pushes Matanbuchus malware, leads to Cobalt Strike

Published: 2022-06-17
Last Updated: 2022-06-17 03:54:44 UTC
by Brad Duncan (Version: 1)
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On Thursday 2022-06-16, threat researchers discovered a wave of malicious spam (malspam) pushing Matanbuchus malware:

Today's diary reviews the activity, which led to Cobalt Strike in my lab environment.

Shown above:  Flow chart for Matanbuchus activity on Thursday 2022-06-16.

Email and Attachment

Shown above:  Screenshot from one of the emails pushing Matanbuchus on 2022-06-16.

Shown above:  The email attachment is a zip archive that contains an HTML file.

Shown above:  The HTML file pretends to be a OneDrive page, however, the HTML file actually contains base64 text that is converted to a file for download.

Shown above:  Zip archive downloaded from the HTML file contains an MSI package.

Shown above:  MSI extracted from the second zip archive is signed using a certificate, apparently from Digicert.

Running the MSI Package

Shown above:  MSI package pretends to install an Adobe font pack.

Shown above:  Installation process presents a fake error message.

Shown above:  VBS file that generated the fake error message, and the Matanbuchus DLL saved to the infected host in two different locations.

NOTE: In the above image, the Matanbuchus file main.dll was dropped by the .msi package, while 2100.nls was retrieved through HTTPS traffic after main.dll was run.  Both have the same SHA256 hash.

Shown above:  Scheduled task to keep the Matanbuchus malware persistent.

Traffic From an Infected Windows Host

Shown above:  Traffic from an infected Windows host filtered in Wireshark (part 1 of 2).

Shown above:  Traffic from an infected Windows host filtered in Wireshark (part 2 of 2).

Indicators of Compromise (IOCs)

SHA256 hashes for 7 unique attachments from 14 email examples on 2022-06-16:

  • 72426e6b8ea42012675c07bf9a2895bcd7eae15c82343b4b71aece29d96a7b22
  • 6b2428fcf9e3a555a3a29fc5582baa1eda15e555c1c85d7bef7ac981d76b6068
  • af534b21a0a0b0c09047e1f3d4f0cdd73fb37f03b745dbb42ffd2340a379dc42
  • b9720e833fa96fec76f492295d7a46b6f524b958278d322c4ccecdc313811f11
  • 23fe3af756e900b5878ec685b2c80acd6f821453c03d10d23871069b23a02926
  • 53af0319d68b0dcbf7cb37559ddfd70cce8c526614c218b5765babdc54500a49
  • 4242064d3f62b0ded528d89032517747998d2fe9888d5feaa2a3684de2370912

SHA256 hashes for HTML files extracted from the above 7 zip archives:

  • d0e2e92ec9d3921dc73b962354c7708f06a1a34cce67e8b67af4581adfc7aaad  SCAN-016063.html
  • 56ec91b8e594824a678508b694a7107d55cf9cd77a1e01a6a44993836b40ec7a  SCAN-026764.html
  • cc08642ddbbb8f735a3263180164cda6cf3b73a490fc742d5c3e31130504e97c  SCAN-068589.html
  • e3b98dac9c4c57a046c50ce530c79855c9fe4025a9902d0f45b0fb0394409730  SCAN-231112.html
  • c117b17bf187a3d52278eb229a1f2ac8a73967d162ad0cfc55089d304b1cc8a7  SCAN-287004.html
  • 82add858e5a64789b26c77e5ec4608e1f162aacbc9163920a0d4aa53eb3e9713  SCAN-446993.html
  • 5708dced57f30ff79e789401360300fe3d5bdcf8f988ede6539b9608dfeb58fd  SCAN-511007.html

SHA256 hashes for zip archives generated by the above 7 HTML files:

  • 63242d49d842cdf699b0ec04ad7bba8867080f8337d3e0ec7e768d10573142b3
  • 6c5eb5d9a66200f0ab69ee49ba6411abf29840bce00ed0681ec8b48e24fd83da
  • ef4ea3976bad1cd68a2da2d926677c0cb04f4fc6e0b629b9a29a1c61ae984c46
  • 19bbebd1e8ec335262e846149a893f4ce803f201e4dee7f3770d95287f9245f3
  • de26167160e7df91bbd992a3523ea6a82049932b947452bb58e9eed3011c769a
  • 7f0bf9496f21050fbc1a3ce5ad35dc300f595c71ad9e73ff5fc5c06b2e35a435
  • 1bc74dfb2142e4929244c6c7e10415664d4e71a5301eaf8e03cb426fab0876f8

SHA256 hashes for .msi packages extracted from the above 7 zip archives:

  • face46e6593206867da39e47001f134a00385898a36b8142a21ad54954682666  SCAN-016063.pdf.msi
  • e22ec74cd833a85882d5a8e76fa3b35daff0b7390bfbcd6b1ab270fd3741ceea  SCAN-026764.pdf.msi
  • 2d8740ea16e9457a358ebea73ad377ff75f7aa9bdf748f0d801f5a261977eda4  SCAN-068589.pdf.msi
  • 5dcbffef867b44bbb828cfb4a21c9fb1fa3404b4d8b6f4e8118c62addbf859da  SCAN-231112.pdf.msi
  • c6e9477fd41ac9822269486c77d0f5d560ee2f558148ca95cf1de39dea034186  SCAN-287004.pdf.msi
  • 4fd90cf681ad260f13d3eb9e38b0f05365d3984e38cfba28f160b0f810ffd4d3  SCAN-446993.pdf.msi
  • 7e37d028789ab2b47bcab159da6458da2e8198617b0e7760174e4a0eea07d9c9  SCAN-511007.pdf.msi

32-bit DLL for Matanbuchus:

SHA256 hash: f8cc2cf36e193774f13c9c5f23ab777496dcd7ca588f4f73b45a7a5ffa96145e

  • File size: 410,624 bytes
  • File location: hxxps://telemetrysystemcollection[.]com/m8YYdu/mCQ2U9/auth.aspx
  • File location: C:\Users\[username]\AppData\Local\AdobeFontPack\main.dll
  • File location: C:\Users\[username]\AppData\Local\x86\[4 ASCII characters for hex].nls
  • File type: PE32 executable (DLL) (console) Intel 80386, for MS Windows
  • Run method: regsvr32.exe [filename]

Note: The above DLL was dropped by the .msi package, then it was also retrieved over HTTPS from telemetrysystemcollection[.]com. The HTTPS traffic is probably a way to update the DLL, but in this case, the new file had the same file hash as the original.

Second file sent over HTTPS traffic from telemetrysystemcollection[.]com:

SHA256 hash: 39ec827d24fe68d341cff2a85ef0a7375e9c313064903b92d4c32c7413d84661

  • File size: 832,128 bytes
  • File location: hxxps://telemetrysystemcollection[.]com/m8YYdu/mCQ2U9/home.aspx
  • File type: base64 text

SHA256 hash: a5b06297d86aee3c261df7415a4fa873f38bd5573523178000d89a8d5fd64b9a

  • File size: 605,184 bytes
  • File description: XOR-ed binary converted from the above base64 text
  • File type: data
  • Note: This binary XOR-ed with the ASCII string: FuHZu4rQgn3eqLZ6FB48Deybj49xEUCtDTAmF

SHA256 hash: bd68ecd681b844232f050c21c1ea914590351ef64e889d8ef37ea63bd9e2a2ec

  • File size: 605,184 bytes
  • File type: PE32 executable (DLL) (console) Intel 80386, for MS Windows
  • File description: DLL file converted from the above XOR-ed binary
  • Note: Unknown entry point for this DLL file

First Cobalt Strike file (ASCII text):

SHA256 hash: 4ee7350176014c7fcb8d33a79dcb1076794a2f86e9b2348f2715ca81f011e799

  • File size: 1,668 bytes
  • File location: hxxp://144.208.127[.]245/cob23_443.txt
  • File type: ASCII text, with very long lines, with no line terminators

SHA256 hash: 7643468adbc1fca4342b7458f0e1dc4ae11c0dde7c06e52fea02c1e057314def

  • File size: 834 bytes
  • File type: data
  • File description: above ASCII text entered into hex editor converted to data binary

Second Cobalt Strike file (32-bit DLL):

SHA256 hash: 6d3259011b9f2abd3b0c3dc5b609ac503392a7d8dea018b78ecd39ec097b3968

  • File size: 16,384 bytes
  • File location: hxxp://144.208.127[.]245/cob_220_443.dll
  • File type: PE32 executable (DLL) (GUI) Intel 80386, for MS Windows
  • Run method: regsvr32.exe [filename]

Infection traffic:

Traffic for Matanbuchus DLL:

  • 213.226.114[.]15 port 443 (HTTPS) - telemetrysystemcollection[.]com - GET /m8YYdu/mCQ2U9/auth.aspx

Additional traffic returning base64 text for XOR-encoded binary:

  • 213.226.114[.]15 port 443 (HTTPS) - telemetrysystemcollection[.]com - GET /m8YYdu/mCQ2U9/home.aspx

Matanbuchus C2 traffic:

  • 213.226.114[.]15 port 48195 (HTTP) - collectiontelemetrysystem[.]com - POST /cAUtfkUDaptk/ZRSeiy/requets/index.php

Traffic caused by Matanbuchus for Cobalt Strike:

  • 144.208.127[.]245 port 80 - 144.208[.]127.245 - GET /cob23_443.txt
  • 144.208.127[.]245 port 80 - 144.208[.]127.245 - GET /cob_220_443.dll

First Cobalt Strike C2 traffic:

  • 185.217.1[.]23 port 443 - hxxps://extic[.]icu/empower/type.tiff
  • 185.217.1[.]23 port 443 - hxxps://extic[.]icu/[unknown]

Second Cobalt Strike C2 traffic:

  • 190.123.44[.]220 port 443 - hxxps://reykh[.]icu/load/hunt.jpgv
  • 190.123.44[.]220 port 443 - hxxps://reykh[.]icu/thaw.txt

Note: The above Cobalt Strike activity did not generate any DNS traffic for the associated .icu domains.

Final Words

14 email examples, a packet capture (pcap) of traffic from an infected Windows host, and the associated malware/artifacts can be found here.

Brad Duncan
brad [at]

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