Threat Level: green Handler on Duty: Xavier Mertens

SANS ISC: Internet Storm Center - Internet Security | DShield Internet Storm Center


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"Blocked" Does Not Mean "Forget It"

Published: 2018-05-24
Last Updated: 2018-05-24 07:16:52 UTC
by Xavier Mertens (Version: 1)
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Today, organisations are facing regular waves of attacks which are targeted... or not. We deploy tons of security controls to block them as soon as possible before they successfully reach their targets. Due to the amount of daily generated information, most of the time, we don’t care for them once they have been blocked. A perfect example is blocked emails. But “blocked” does not mean that we can forget them, there is still valuable information in those data.

Tons of emails are blocked by your <name_your_best_product> solution and you’re feeling safe. Sometimes, one of them isn’t detected and is dropped in the user’s mailbox but you have an incident handling process or the user simply deletes it because he/she got a security awareness training. Everybody is happy in this wonderful world.

What if your organization was targeted and spear phishing emails were received and (hopefully) blocked? A good idea is to review those blocked emails on a daily basis and to search for interesting keywords that could indicate a specifically crafted message targeting the organization. 

Interesting keywords to search for could be:

  • Your domain names

  • Your brands

  • Terms related to your business (health, finance, government, …)

  • ...

If such messages are detected, they could be a good indicator that something weird will happen and to take appropriate actions like raising your SOC DEFCON[1] level or proactively warn users that spear phishing campaigns are ongoing.

Stay safe!

[1] https://en.wikipedia.org/wiki/DEFCON

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

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