Kids Like Cookies, Malware Too!

Published: 2022-09-23
Last Updated: 2022-09-23 08:41:43 UTC
by Xavier Mertens (Version: 1)
1 comment(s)

Recently, a vulnerability has been disclosed by Vectra that affects Microsoft Teams[1], the very popular communication tool used daily by millions of people (me too). Security researchers found that Teams stores session tokens in clear text on the file system. I won’t discuss the vulnerability here; read the blog post if you want to learn more. The critical element is that once the token has been stolen, an attacker can impersonate the user.

At the end of the blog post, Vectra lists interesting files to watch on the file system. For the Windows operating system, there are:

%AppData%\Microsoft\Teams\Cookies
%AppData%\Microsoft\Teams\Local Storage\leveldb

After reading this, I was curious to see if this is already exploited in the wild. I created a new hunting rule on VT and crossed my fingers. After a few false positives, I got a hit! A DLL was uploaded and contained one of the two strings above.

The file was called “RwWork.dll” (SHA256:5092a18330debda930a73835c8e77c6a7fb3a5904bdc04aad61c6c4136f0d24b). It currently has a VT score of 56/71[2]. The file looks indeed for Teams cookies but even more:

As you can see, many files related to cookies are searched. The malware is from the Floxif family...

[1] https://www.vectra.ai/blogpost/undermining-microsoft-teams-security-by-mining-tokens
[2] https://www.virustotal.com/gui/file/5092a18330debda930a73835c8e77c6a7fb3a5904bdc04aad61c6c4136f0d24b/details

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

1 comment(s)
ISC Stormcast For Friday, September 23rd, 2022 https://isc.sans.edu/podcastdetail.html?id=8186

Comments

What's this all about ..?
password reveal .
<a hreaf="https://technolytical.com/">the social network</a> is described as follows because they respect your privacy and keep your data secure:

<a hreaf="https://technolytical.com/">the social network</a> is described as follows because they respect your privacy and keep your data secure. The social networks are not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go.

<a hreaf="https://technolytical.com/">the social network</a> is not interested in collecting data about you. They don't care about what you're doing, or what you like. They don't want to know who you talk to, or where you go. The social networks only collect the minimum amount of information required for the service that they provide. Your personal information is kept private, and is never shared with other companies without your permission
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Enter comment here... a fake TeamViewer page, and that page led to a different type of malware. This week's infection involved a downloaded JavaScript (.js) file that led to Microsoft Installer packages (.msi files) containing other script that used free or open source programs.
distribute malware. Even if the URL listed on the ad shows a legitimate website, subsequent ad traffic can easily lead to a fake page. Different types of malware are distributed in this manner. I've seen IcedID (Bokbot), Gozi/ISFB, and various information stealers distributed through fake software websites that were provided through Google ad traffic. I submitted malicious files from this example to VirusTotal and found a low rate of detection, with some files not showing as malware at all. Additionally, domains associated with this infection frequently change. That might make it hard to detect.
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