The Guloader sample in question uses the control flow obfuscation technique to hide its functionalities and evade detection.
This technique impedes both static and dynamic analysis.
First, looking at how this threat hampers static analysis. In short, it uses CPU instructions that trigger exceptions, resulting in unintelligible code during static analysis.
After peeling away the packer layer of Guloader sample, analysts see that its code is obfuscated.
Using static analysis tools such as IDA Pro, analysts observe many 0xCC bytes (or int3 instructions) littered throughout the sample.
Following the 0xCC bytes are junk instructions. These added bytes disrupt the static analysis tool’s disassembly process, resulting in the wrong disassembly listing.
0xCC bytes are CPU instructions that trigger an exception EXCEPTION_BREAKPOINT (0x80000003), which pauses the execution of a process.
The CPU will pass the code flow to the handler function before the execution continues. The handler function is responsible for moving the instruction pointer to the correct address.
The presence of these same 0xCC bytes make it so that using a debugger during dynamic analysis would crash the Guloader sample. Debuggers insert 0xCC bytes as software breakpoints to halt the execution of the sample. The debugger handles the exception instead of the handler function.
Before understanding what happens in the handler function, analysts first have to locate its address.
Guloader uses the AddVectoredExceptionHandler function to register the handler function.
The second argument of the AddVectoredExceptionHandler function points to the address of the handler function.
Using a debugger, analysts locate the address of the handler function registered by the Guloader sample. With the address information, analysts can examine its code.
Notably, this ExceptionHandler is registered with the order of 1, meaning it is the first handler to be invoked.
Sign Up For Threat Alerts
Jul 04, 2023
Rhysida Ransomware RaaS Crawls Out of Crimeware...
The Rhysida ransomware-as-a-service (RaaS) group has gone from a dubious newcomer to a fully-fledged ransomware...
Jun 26, 2023
Operation Magalenha – Long-Running Campaign Pursues Portuguese...
The attackers can steal credentials and exfiltrate users' data and personal information, which can be...
Apr 24, 2023
Lazarus Group Adds Linux Malware to Arsenal...
Researchers have discovered a new campaign conducted by Lazarus, known as "Operation DreamJob," which targets...
Apr 23, 2023
Additional IOCs for 3cx breach
Recently an unexpected malicious activity emanating from a legitimate, signed binary, 3CXDesktopApp was observed.
Apr 23, 2023
Ex-Conti and FIN7 Actors Collaborate with New...
IBM Security X-Force recently discovered a new malware family Analysts have called "Domino," which Analysts...
Apr 20, 2023
AuKill EDR killer malware abuses Process Explorer...
The AuKill tool abuses an outdated version of the driver used by version 16.32 of...
Apr 20, 2023
Fake Chrome updates spread malware
A campaign running since the end of last year is using hacked sites to push...
Apr 20, 2023
QBot using new attack vector in its...
QBot, also known as QakBot, previously operated as a banking trojan and has since transformed...
Apr 20, 2023
CrossLock Ransomware Emerges: New Golang – Based...
The CrossLock ransomware employs the double extortion technique to increase the likelihood of payment from...
Apr 20, 2023
Windows Zero-Day Vulnerability CVE-2023-28252 Exploited by Nokoyawa...
A zero-day vulnerability in the Microsoft Windows system, which also affects Windows 11, has been...
Apr 18, 2023
Additional IOcs for 3cx breach
Recently an unexpected malicious activity emanating from a legitimate, signed binary, 3CXDesktopApp was observed. As...
Apr 18, 2023
Additional IOcs for 3cx breach
Recently an unexpected malicious activity emanating from a legitimate, signed binary, 3CXDesktopApp was observed. As...
Apr 18, 2023
APT36 Expands Interest Within Indian Education Sector
Symantec described UPS in 2016 report as Buckeye (also known as APT3 Gothic Panda UPS...
Apr 17, 2023
ChinaZ DDoS Bot Malware Distributed To Linux...
The ChinaZ DDoS bot malware was discovered targeting Linux systems while a version for Microsoft...
Apr 16, 2023
Resurgence Of The Mexals Cryptojacking Campaign
The Mexals crypto jacking campaign has been in operation since at least 2021 and continues...