Dark Reading is part of the Informa Tech Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them.Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.

Vulnerabilities / Threats

11/24/2020
05:50 PM
Connect Directly
Twitter
LinkedIn
RSS
E-Mail
50%
50%

Latest Version of TrickBot Employs Clever New Obfuscation Trick

The malware takes advantage of how the Windows command line interpreter works to try and slip past anti-detection tools, Huntress Labs says.

Researchers at Huntress Labs have uncovered what they described as a really clever use of Windows batch scripting by the authors of Trickbot to try and sneak the latest version of their malware past automated detection tools.

The technique takes advantage of the way the Windows command line interpreter, cmd [.] exe, reads and interprets data that is typed on the command line.  

Related Content:

JavaScript Obfuscation Moves to Phishing Emails

The Changing Face of Threat Intelligence

New on The Edge: How Industrial IoT Security Can Catch Up With OT/IT Convergence

What the authors of Trickbot have done is use a batch script to break up their payload into numerous small chunks and then use the command line interpreter to rebuild the original payload, says John Hammond, senior security researcher at Huntress.

"The gist of this technique is substituting each character in a payload with a new mapped value, so the payload can be slowly created with building blocks."

This technique isn't specific to Trickbot. In fact, any other code or malware sample can do this within Windows batch scripting, Hammond says. But this is the first time that Huntress has observed a threat actor using this exact obfuscation technique, he says. "It seems to be a very simple technique, and now that Trickbot has introduced it, it may become more popular."

Though PowerShell and other command line tools are now available for Windows, cmd [.] exe remains the default command line interpreter for the operating system, as it has for decades. The technology makes a good target for attackers because it provides an interactive interface that they can use to execute commands, run malicious programs, delete files, and carry out a variety of other actions.

Typically, the command prompt can be hardened and locked down with application whitelisting or more secure configuration settings, Hammond notes. "But if a threat actor can access it, it is really a high-value target," because of the extent of control that it allows an attacker to establish over the operation system.

According to Huntress, the batch script that Trickbot authors have used to obfuscate their payload looks like a whole of lot of garbled code with random letters and weird percent signs scattered all over. But a closer examination of the code showed that it is designed to create small, one-letter or two-character variable values that are small chunks of the final payload. Though the code might look completely unintelligible, cmd [.] exe interprets it and executes it.

Troublingly, to an automated scanner, the multiple, smaller chunks would not appear like any malicious strings, so the malware would be able to evade detection. "This obfuscated loader primarily evades signature-based detection — which hunts for known bad strings or characters that can indicate malicious activity," Hammond says.

For organizations, the main takeaway is that automated tools don't guarantee protection against all malware threats. In this case, the obfuscation that the authors of Trickbot employed would have been relatively easy to spot for human analysts. But a scanner might not see any evidence of malicious or bad commands and let the malware slip past, Hammond says.

"A real person might look at this batch script and say, 'oh, if you just add this command right here, it spits out the payload and tells you what exactly it is trying to do,'" he says. "Automated solutions do not and cannot think to do that."

Jai Vijayan is a seasoned technology reporter with over 20 years of experience in IT trade journalism. He was most recently a Senior Editor at Computerworld, where he covered information security and data privacy issues for the publication. Over the course of his 20-year ... View Full Bio
 

Recommended Reading:

Comment  | 
Print  | 
More Insights
Comments
Newest First  |  Oldest First  |  Threaded View
NSA Appoints Rob Joyce as Cyber Director
Dark Reading Staff 1/15/2021
Register for Dark Reading Newsletters
White Papers
Video
Cartoon Contest
Current Issue
2020: The Year in Security
Download this Tech Digest for a look at the biggest security stories that - so far - have shaped a very strange and stressful year.
Flash Poll
Assessing Cybersecurity Risk in Today's Enterprises
Assessing Cybersecurity Risk in Today's Enterprises
COVID-19 has created a new IT paradigm in the enterprise -- and a new level of cybersecurity risk. This report offers a look at how enterprises are assessing and managing cyber-risk under the new normal.
Twitter Feed
Dark Reading - Bug Report
Bug Report
Enterprise Vulnerabilities
From DHS/US-CERT's National Vulnerability Database
CVE-2021-22847
PUBLISHED: 2021-01-22
Hyweb HyCMS-J1's API fail to filter POST request parameters. Remote attackers can inject SQL syntax and execute commands without privilege.
CVE-2021-22849
PUBLISHED: 2021-01-22
Hyweb HyCMS-J1 backend editing function does not filter special characters. Users after log-in can inject JavaScript syntax to perform a stored XSS (Stored Cross-site scripting) attack.
CVE-2020-8567
PUBLISHED: 2021-01-21
Kubernetes Secrets Store CSI Driver Vault Plugin prior to v0.0.6, Azure Plugin prior to v0.0.10, and GCP Plugin prior to v0.2.0 allow an attacker who can create specially-crafted SecretProviderClass objects to write to arbitrary file paths on the host filesystem, including /var/lib/kubelet/pods.
CVE-2020-8568
PUBLISHED: 2021-01-21
Kubernetes Secrets Store CSI Driver versions v0.0.15 and v0.0.16 allow an attacker who can modify a SecretProviderClassPodStatus/Status resource the ability to write content to the host filesystem and sync file contents to Kubernetes Secrets. This includes paths under var/lib/kubelet/pods that conta...
CVE-2020-8569
PUBLISHED: 2021-01-21
Kubernetes CSI snapshot-controller prior to v2.1.3 and v3.0.2 could panic when processing a VolumeSnapshot custom resource when: - The VolumeSnapshot referenced a non-existing PersistentVolumeClaim and the VolumeSnapshot did not reference any VolumeSnapshotClass. - The snapshot-controller crashes, ...