Stephan Berger Profile picture
Jun 16 11 tweets 3 min read Twitter logo Read on Twitter
1/ We recently had an interesting #Azure case where the TA, instead of creating a new Inbox Rule, added email addresses of interest to the list of blocked senders and domains.

The incoming emails will get flagged as spam and moved to the Junk email folder. 📂

🧵
2/ Here is a screenshot from Outlook web access

(the view might differ, as, for example, here on the screenshot from the theitbros [1]) Image
3/ And here from an Outlook client: Image
4/ This is a sneaky way to circumvent monitoring of audit logs which looks for specific keywords like "New-InboxRule".

Check out the excellent Business Email Compromise (BEC) guide from PwC for more keywords and background. [2]
5/ Plus, such a rule will not appear when extracting mailbox rules from the compromised account (or for all accounts for threat-hunting reasons) with the cmdlet Get-InboxRule.
6/ But we see this action in the Unified Audit Log tracked with the Operation "Set-MailboxJunkEmailConfiguration" Image
7/ Or we can read out the active list of blocked senders and domains with PowerShell (might return a long list of domains and addresses):

Get-MailboxJunkEmailConfiguration -Identity $Mailbox.Alias | Format-List BlockedSendersAndDomains
8/ I tweeted about the "Set-MailboxJunkEmailConfiguration" operation before, but last time, the attackers entered a whole list of mail addresses as trusted senders to facilitate receiving spam mail.

9/ Unfortunately, the client had auditing turned off - so there is no easy UAL way to backtrack the attacker's steps.

10/ Nevertheless, the TA must log into the compromised account to read the "interesting" emails received and move to the Junk-Folder (because of the Blocked Senders rule).

Thus we still have a good chance to catch the TA with the traces inside the Sign-In Logs 🎉

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More from @malmoeb

Apr 18
1/ Customer receives an email from a network monitoring device that a host is supposedly infected with a #CoinMiner. The Task Manager on the said system shows the following screenshot 🤕.

A story of an unpatched system, incorrect scoping, and 🍀. 🧵

#CyberSecurity Image
2/ The affected (and remotely accessible) server have had Confluence installed.

One of my first questions I asked the customer was if the system was up to date (Spoiler: it wasn't).

Confluence 6.0.4 was installed at the time of the incident.
3/ Confluence 6.0.4 was released in January 2017 🤯 Image
Read 14 tweets
Apr 17
1/ I used #AutoRuns v14.09 (GUI) in my lab setup but noticed that it failed to find (or display) the malware in the Startup folder, although the file is there (screenshot below).

I checked back and forth, searched manually for the file, and restarted the OS and AutoRuns.

🧵 Image
2/ With #Velociraptor, I ran the hunt Sysinternals.Autoruns, and with the CLI version of AutoRuns, the malware is found in the Startup folder. Image
3/ The same for the #Velociraptor hunt Sys.StartupItems. Image
Read 4 tweets
Mar 21
1/ The content below is from a file named install.bat and stems from a recent investigation where a TA launched this batch file. 👀

What's going on?

Well, VboxUpdate.exe is, in fact, tor.exe, and a new service is created, launching tor with a config file.

🧵 #CyberSecurity Image
2/ Below is an excerpt from the content of config.txt; the configuration file passed as an argument to the tor service.

If you think this looks a lot like RDP Tunneling, you are absolutely right. 🥇 Image
3/ Head over to the allthingsdfir blog to read a more profound write-up about the techniques used here and how they work together.

allthingsdfir.com/rdp-over-tor/
Read 5 tweets
Mar 20
1/ Real-World #PingCastle Finding #13: Allow log on locally

➡️ Domain Users are eligible to log into DC's 🤯🙈

"When you grant an account the Allow logon locally right, you are allowing that account to log on locally to all domain controllers in the domain." [1]

#CyberSecurity Image
2/ Why is this a bad idea?

"If you do not restrict this user right to legitimate users who must log on to the console of the computer, unauthorized users could download and run malicious software to elevate their privileges." [1]
3/ I encountered this finding several times in our AD assessments, so you better check your settings in your domain right now (better safe than sorry 🔒).

Good luck 🍀
Read 4 tweets
Mar 18
1/ Do you monitor newly created services within your environment, and would you notice when a (vulnerable) driver is loaded?

The screenshot below (#Velociraptor 🤩) is from a recent #XMRig CoinMiner investigation ⤵️

🧵 #CyberSecurity
2/ We talked about vulnerable drivers before:

Read 4 tweets
Mar 17
1/ #Velociraptor has covered hunting for malicious WMI Event Consumers for some time. [1]

However, Velociraptor does not provide an eradication hunt for malicious WMI Event Consumers out of the box.

🧵 #CyberSecurity
2/ @threatpunter wrote a detailed blog about WMI persistences and how to remove them.

"The simplest method to remove the entry from the WMI database is to use Autoruns. Launch Autoruns as an administrator and select the WMI tab to review WMI-related persistence." ✂️ Image
3/ "Alternatively, you can remove the WMI event subscriptions from the command line." [2] Image
Read 4 tweets

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