Malware Tricks to Avoid Detection by using Big Junk Data and Activates a Backdoor

[jpshare]A New technique used by Malware authors by Creating More unwanted junk file embedded with Malicious payload which leads to Avoid Detection by AV. Those unwanted Garbage files contains more than 100 MB junk files.

According to the Researchers from Kaspersky ,attacker has been using the XXMM malware toolkit and this sample has a very big overlay of junk data and 20 other similar samples are collected by YARA Rules.

This Malware identified as a Trojan loader which leads to Open a Backdoor in Victim Machine and the Backdoor name is Discovered as a “wali”

config strings with “[wali]” [souce :Kaspersky]

According to Kaspersky The size of one wali loader (MD5:d1e24c3cc0322b22988a1ce366d702e5) was initially 1,124,3,52 bytes. The function that appends garbage produced a new malware file in a real attack (MD5: 8bd0ddeb11518f3eaaddc6fd82627f33) and the file size was increased to 105,982,049 bytes.

What is inside the wali loader:

its contains more then 100 MB of non related junk files  is the Reason Behind of the Wali loader’s big Size Backdoor .

According to Researchers ShadowWali was an earlier version of Wali. The fact that ShadowWali only supported 32-bit architectures, while Wali runs on both 32-bit and 64-bit systems.

The wali loader is installed onto the victim’s machine when the overlay data is generated by the wali dropper.

Structure of wali modules [Source:Kaspersky]

“Wali dropper1 checks the CPU architecture. If the CPU is 64-bit, this malware decrypts the 64-bit version of the wali loader from resource id 101. Otherwise, it decrypts the 32-bit version of the wali loader from resource id 102″

Based Upon the Random Values Malware junk size may Differ betweek 50 MB to 200 MB.

Some of sample Malware Detected by Kaspersky,

• Trojan.Win32.Xxmm
• Trojan.Win64.Xxmm
• Trojan-Downloader.Win32.Xxmm
• Trojan-Downloader.Win64.Xxmm
• Trojan-Dropper.Win32.Xxmm
• Trojan-Dropper.Win64.Xxmm

 Once ShadowWali or Wali are installed, the malware injects itself into other processes.

In most infections, the process of choice has been Internet Explorer (iexplorer.exe), but there have been cases where the malware was injected into Windows Explorer (explorer.exe) and the Local Security Authority Subsystem Service (lsass.exe).

Also Researchers said, executable malwares disguised as movie files and ISO files spread over torrents, which in these cases, the malware size is inflated to a few gigabytes in order to mimic true content .

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