Colin Mc Hugo

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Colin Mc Hugo
Security Engineer Manager & CEO at Quantum Infinite Solutions Group Ltd.

This New Malware Family Using CLFS Log Files to Avoid Detection

September 4, 2021
Malware Attack

Cybersecurity researchers have disclosed particulars a couple of new malware household that depends on the Widespread Log File System (CLFS) to cover a second-stage payload in registry transaction information in an try and evade detection mechanisms.

FireEye’s Mandiant Superior Practices crew, which made the invention, dubbed the malware PRIVATELOG, and its installer, STASHLOG. Specifics concerning the identities of the risk actor or their motives stay unclear.

Though the malware is but to be detected in real-world assaults geared toward buyer environments or be noticed launching any second-stage payloads, Mandiant suspects that PRIVATELOG might nonetheless be in growth, the work of a researcher, or deployed as a part of a extremely focused exercise.

CLFS is a general-purpose logging subsystem in Home windows that is accessible to each kernel-mode in addition to user-mode functions akin to database programs, OLTP programs, messaging purchasers, and community occasion administration programs for constructing and sharing high-performance transaction logs.

“As a result of the file format isn’t broadly used or documented, there aren’t any accessible instruments that may parse CLFS log information,” Mandiant researchers explained in a write-up revealed this week. “This supplies attackers with a possibility to cover their information as log data in a handy manner, as a result of these are accessible by way of API features.”

PRIVATELOG and STASHLOG include capabilities that permit the malicious software program to linger on contaminated units and keep away from detection, together with the usage of obfuscated strings and management circulation methods which might be expressly designed to make static evaluation cumbersome. What’s extra, the STASHLOG installer accepts a next-stage payload as an argument, the contents of that are subsequently stashed in a selected CLFS log file.

Long-established as an un-obfuscated 64-bit DLL named “prntvpt.dll,” PRIVATELOG, in distinction, leverages a method referred to as DLL search order hijacking to be able to load the malicious library when it’s referred to as by a sufferer program, on this case, a service referred to as “PrintNotify.”

“Equally to STASHLOG, PRIVATELOG begins by enumerating *.BLF information within the default person’s profile listing and makes use of the .BLF file with the oldest creation date timestamp,” the researchers famous, earlier than utilizing it to decrypt and retailer the second-stage payload.

Mandiant recommends that organizations apply YARA guidelines to scan inner networks for indicators of malware and be careful for potential Indicators of Compromise (IoCs) in “course of”, “imageload” or “filewrite” occasions related to endpoint detection and response (EDR) system logs.

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