Threat Level: green Handler on Duty: Johannes Ullrich

SANS ISC: InfoSec Handlers Diary Blog InfoSec Handlers Diary Blog


Sign Up for Free!   Forgot Password?
Log In or Sign Up for Free!

Keep an Eye on Remote Access to Mailboxes

Published: 2019-10-30
Last Updated: 2019-10-30 09:13:03 UTC
by Xavier Mertens (Version: 1)
3 comment(s)

BEC or "Business Email Compromize" is a trending thread for a while. The idea is simple: a corporate mailbox (usually from a C-level member) is compromized to send legitimate emails to other employees or partners. That's the very first step of a fraud that could have huge impacts.

This morning, while drinking some coffee and reviewing my logs, I detected a peak of rejected authentications against my mail server. There was a peak of attempts but also, amongst the classic usernames, bots tested some interesting alternatives. If the username is "firstname", I saw attempts to log in with:

firstname
okfirstname
mailfirstname
emailfirstname
firstnamemail
domain_firstname
...

And also the classic generic mailboxes ('noreply', 'info', webmaster', 'admin', etc)

The peak of activity was interesting:

Email remains an easy attack vector and is often very easy to compromise. Access to a corporate mailbox can be disastrous based on what people store in their mailbox (documents, passwords, pictures, etc) and mail servers remain often available in the wild. Keep an eye on remote accesses to mailboxes, especially for sensitive accounts! (Do you remember my diary about considering people as IOC's?[1])

[1] https://isc.sans.edu/forums/diary/May+People+Be+Considered+as+IOC/25166/

Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key

3 comment(s)
Diary Archives