Huntress Explains TrickBot’s Obfuscated Windows Batch Launcher
Summary
Huntress analyzed a TrickBot v100 launcher that uses Windows batch variables to obscure a command. The article explains how the script reconstructs a command to start the malware executable and why the obfuscation may challenge automated detection.
Key points
- Huntress described a batch-script launcher associated with TrickBot v100.
- The script uses cmd.exe variable expansion to assemble pieces of a command from scattered values.
- The reconstructed command starts an executable in a user’s AppData\Roaming\Identities directory.
- Huntress identified the launched executable, ulib8b4.exe, as TrickBot.
- The article says the obfuscation could make malicious commands less apparent to signature-based antivirus or EDR tools.
- An analyst can make the script’s final command readable by echoing it rather than executing it.
Article Details
- Attack Vectors
- A batch-script launcher for TrickBot used cmd.exe variable expansion to assemble and execute a command while obscuring its contents.
- The decoded command started the executable C:\Users\****\AppData\Roaming\Identities1603031315\ulib8b4.exe.
- Defensive Notes
- The article recommends human analysis of suspicious code alongside automated defenses, since signature-based antivirus and EDR may not recognize this obfuscation.
- Use layered security controls rather than relying on a single defensive tool.
MITRE ATT&CK
T1027 · Obfuscated Files or InformationThe TrickBot launcher obscures its command by defining variables containing character fragments and expanding them together in a batch script.T1059.003 · Windows Command ShellThe launcher uses Windows Command Prompt batch scripting and cmd.exe variable expansion to execute the assembled start command.