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[LUG] OT: XLL file (Excel Add-ins) malware

 

Having just updated a Linux mail server to reject ".xll" file attachments in 
emails I got to wondering if this is a new vector for infection, or just under 
used? I received a couple of emails today with .XLL attachments, obviously 
malicious.

 XLL files have been around since the 90s, but this is the first time I added it 
to my filter, and I usually cull unusual file attachments actually used in 
malware campaigns to stop others without a need for the format from tripping 
up too easily.

Obviously doing this in a mail server doesn't stop people sending it via 
encrypted emails, emails with links, file shares, torrents, etc, but does stop 
simple attachments. The users needing protection most are the ones least 
likely to be able to save and decrypt an encrypted attachment.

A quick search brought it up as being used for malware in July 2021 via a 
different attack vector, so I'm guessing that has attracted attention to the 
format's utility for infection of Excel users.

https://isc.sans.edu/forums/diary/Hancitor+tries+XLL+as+initial+malware+file/
27618/





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