Introduction Back in January 2021, law enforcement and judicial authorities worldwide took down the Emotet botnet. Although some Emotet emails still went out in the weeks after that, those were remnants from the inactive botnet infrastructure. We hadn't seen any new Emotet since then. But on Monday 2021-11-15, we saw indicators that Emotet has returned. This diary reviews activity from a recent Emotet infection.
Emails We found some emails from a newly-revived Emotet botnet on Monday 2021-11-15 that have one of three types of attachments:
These emails were all spoofed replies that used data from stolen email chains, presumably gathered from previously infected Windows hosts.
Infection traffic Infection traffic for Emotet is similar to what we saw before the takedown in January 2021. The only real difference is Emotet post-infection C2 is now encrypted HTTPS instead of unencrypted HTTP. My infected lab host turned into a spambot trying to push out more Emotet malspam.
The following are Word documents, Excel files, and a password-protected zip archive I saw from Emotet on Monday 2021-11-15. SHA256 hash: 7c5690577a49105db766faa999354e0e4128e902dd4b5337741e00e1305ced24
SHA256 hash: bd9b8fe173935ad51f14abc16ed6a5bf6ee92ec4f45fd2ae1154dd2f727fb245
SHA256 hash: f7a4da96129e9c9708a005ee28e4a46af092275af36e3afd63ff201633c70285
SHA256 hash: d95125b9b82df0734b6bc27c426d42dea895c642f2f6516132c80f896be6cf32
SHA256 hash: 88b225f9e803e2509cc2b83c57ccd6ca8b6660448a75b125e02f0ac32f6aadb9
SHA256 hash: 1abd14d498605654e20feb59b5927aa835e5c021cada80e8614e9438ac323601
The following are URLs generated by macros from the above files for an Emotet DLL file:
The Emotet DLL was first stored as a random file name with a .dll extension under the C:\ProgramData directory. Then it was moved to a randomly-named directory under the infected user's AppData\Local folder. The DLL is then made persistent through a Windows registry update as shown below.
SHA256 hashes for 7 examples of Emotet DLL files:
HTTPS Emotet C2 traffic:
Final words The emails examples and malware samples from Monday's Emotet activity on 2021-11-15 can be found here. --- Brad Duncan |
Brad 433 Posts ISC Handler Nov 16th 2021 |
Thread locked Subscribe |
Nov 16th 2021 6 months ago |
Thanks for posting these details. I took the opportunity to educate the people in my organization and encourage them to notify us if they receive email that looks suspicious before opening the attachments. I also "borrowed" or "stole" your diagram describing the flow of the infection. For the visual learners out there this is helpful for them to understand that opening the attachment is all it takes to be infected.
And I always remind them, "We would rather spend a few minutes investigating a message you feel uneasy about rather than open an attachment and spend hours or days rebuilding a system or systems." Thanks and keep up the good work. |
Anonymous |
Quote |
Nov 16th 2021 6 months ago |
Thanks for the detailed analysis and heads-up!
Emotet will abuse established trust between people as well as the "known good" / "accepted domains" configurations that have been implemented to improve communications with customers, partners etc. A strong defense is to simply block macro-enabled Office documents via anti-malware policies, do not forget that this even works for docm/xlsm/pptm files inside password protected ZIP files as the file names are not encrypted. Blocking of macro-enabled documents should not affect users at all because they will be notified that this has been blocked and can find ways around this for legitimate use. Did you mean to send a PDF version, could you share via our collaboration tool etc. docs.microsoft[.]com/en-us/microsoft-365/security/office-365-security/configure-anti-malware-policies?view=o365-worldwide#use-the-microsoft-365-defender-portal-to-create-anti-malware-policies Enable the common attachments filter: If you select this option, messages with the specified attachments are treated as malware and are automatically quarantined. You can modify the default list by selecting Customize file types. THANKS from a long time reader. Tor PS: Yes, old macros come in .XLSX or .XLS files.. But, finally, Microsoft has published techcommunity.microsoft[.]com/t5/excel-blog/restrict-usage-of-excel-4-0-xlm-macros-with-new-macro-settings/ba-p/2528450 and promise that "XLM macros will soon be disabled by default" Users can expect this coming change in default behavior to occur in the following M365 updates: 2021 October Current Channel 2021 December Monthly Enterprise Channel 2022 January Semi-Annual Enterprise Channel (Preview) 2022 July Semi-Annual Enterprise Channel |
dotBATman 70 Posts |
Quote |
Nov 17th 2021 6 months ago |
Sign Up for Free or Log In to start participating in the conversation!