Suspicious FromBase64String Usage On Gzip Archive - Ps Script

calendar Nov 2, 2023 · attack.command_and_control attack.t1132.001  ·
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Detects attempts of decoding a base64 Gzip archive in a PowerShell script. This technique is often used as a method to load malicious content into memory afterward.

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 1title: Suspicious FromBase64String Usage On Gzip Archive - Ps Script
 2id: df69cb1d-b891-4cd9-90c7-d617d90100ce
 3related:
 4    - id: d75d6b6b-adb9-48f7-824b-ac2e786efe1f
 5      type: similar
 6status: test
 7description: Detects attempts of decoding a base64 Gzip archive in a PowerShell script. This technique is often used as a method to load malicious content into memory afterward.
 8references:
 9    - https://speakerdeck.com/heirhabarov/hunting-for-powershell-abuse?slide=43
10author: frack113
11date: 2022/12/23
12tags:
13    - attack.command_and_control
14    - attack.t1132.001
15logsource:
16    product: windows
17    category: ps_script
18    definition: 'Requirements: Script Block Logging must be enabled'
19detection:
20    selection:
21        ScriptBlockText|contains|all:
22            - 'FromBase64String'
23            - 'MemoryStream'
24            - 'H4sI'
25    condition: selection
26falsepositives:
27    - Legitimate administrative script
28level: medium

References

  • Hunting for PowerShell Abuse

    PowerShell is the favorit tool of IT guys, who are responsible for administration of Windows infrastructures. It allows them to manage differen services of the operating system and automate almost anything. But along with administrators, PowerShell also is liked by attackers and malware authors. The reason PowerShell is so attractive for adversaries is quite obvious: it has been included in essentially every Windows operating system by default for a decade, provides access to Windows API, and is rarely constrained, thus allowing adversaries to perform different tasks without risking being blocked. ttackers can use PowerShell to direct the execution of a local script, retrieve and execute remote resources using various network protocols, encode payloads passed via the command line, or load PowerShell into other processes. Because of so prevalence of PowerShell among adversaries for Threat Hunters it is very important to be able to detect malicious uses of PowerShell and defend against it. In the presentation author is going to demostrate an approaches for detection of PowerShell abuses based on different event sources like native Windows logging capabilities as well as usage of additional tools, like Sysmon or EDR solutions. How to collect traces of using PowerShell, how to filter out false positives, and how to find evidence of malicious uses among the remaining after filtering volume of events — all these questions will be answered in the talk for present and future threat hunters.


    Read More

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