The threat actors behind a loader malware called HijackLoader have added new techniques for defense evasion, as the malware continues to be increasingly used by other threat actors to deliver additional payloads and tooling.
"The malware developer used a standard process hollowing technique coupled with an additional trigger that was activated by the parent process writing to a pipe," CrowdStrike researchers Donato Onofri and Emanuele Calvelli said in a Wednesday analysis. "This new approach has the potential to make defense evasion stealthier."
HijackLoader was first documented by Zscaler ThreatLabz in September 2023 as having been used as a conduit to deliver DanaBot, SystemBC, and RedLine Stealer. It's also known to share a high degree of similarity with another loader known as IDAT Loader.
Both the loaders are assessed to be operated by the same cybercrime group. In the intervening months, HijackLoader has been propagated via ClearFake and put to use by TA544 (aka Narwhal Spider, Gold Essex, and Ursnif Gang) to deliver Remcos RAT and SystemBC via phishing messages.
"Think of loaders like wolves in sheep's clothing. Their purpose is to sneak in, introduce and execute more sophisticated threats and tools," Liviu Arsene, director of threat research and reporting at CrowdStrike, said in a statement shared with The Hacker News.
"This recent variant of HijackLoader (aka IDAT Loader) steps up its sneaking game by adding and experimenting with new techniques. This is similar to enhancing its disguise, making it stealthier, more complex, and more difficult to analyze. In essence, they're refining their digital camouflage."
The starting point of the multi-stage attack chain is an executable ("streaming_client.exe") that checks for an active internet connection and proceeds to download a second-stage configuration from a remote server.
The executable then loads a legitimate dynamic-link library (DLL) specified in the configuration to activate shellcode responsible for launching the HijackLoader payload via a combination of process doppelgänging and process hollowing techniques that increases the complexity of analysis and the defense evasion capabilities.
"The HijackLoader second-stage, position-independent shellcode then performs some evasion activities to bypass user mode hooks using Heaven's Gate and injects subsequent shellcode into cmd.exe," the researchers said.
"The injection of the third-stage shellcode is accomplished via a variation of process hollowing that results in an injected hollowed mshtml.dll into the newly spawned cmd.exe child process."
Heaven's Gate refers to a stealthy trick that allows malicious software to evade endpoint security products by invoking 64-bit code in 32-bit processes in Windows, effectively bypassing user-mode hooks.
One of the key evasion techniques observed in HijackLoader attack sequences is the use of a process injection mechanism called transacted hollowing, which has been previously observed in malware such as the Osiris banking trojan.
"Loaders are meant to act as stealth launch platforms for adversaries to introduce and execute more sophisticated malware and tools without burning their assets in the initial stages," Arsene said.
"Investing in new defense evasion capabilities for HijackLoader (aka IDAT Loader) is potentially an attempt to make it stealthier and fly below the radar of traditional security solutions. The new techniques signal both a deliberate and experimental evolution of the existing defense evasion capabilities while also increasing the complexity of analysis for threat researchers."
