Potential Powershell ReverseShell Connection

SIGMA detection rule by FPT.EagleEye, wagga, Nasreddine Bencherchali (Nextron Systems) · NOASSERTION

Detects usage of the "TcpClient" class. Which can be abused to establish remote connections and reverse-shells. As seen used by the Nishang "Invoke-PowerShellTcpOneLine" reverse shell and other.

title: Potential Powershell ReverseShell Connection
id: edc2f8ae-2412-4dfd-b9d5-0c57727e70be
status: stable
description: Detects usage of the "TcpClient" class. Which can be abused to establish remote connections and reverse-shells. As seen used by the Nishang "Invoke-PowerShellTcpOneLine" reverse shell and other.
references:
    - https://www.volexity.com/blog/2021/03/02/active-exploitation-of-microsoft-exchange-zero-day-vulnerabilities/
    - https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/
    - https://github.com/samratashok/nishang/blob/414ee1104526d7057f9adaeee196d91ae447283e/Shells/Invoke-PowerShellTcpOneLine.ps1
author: FPT.EagleEye, wagga, Nasreddine Bencherchali (Nextron Systems)
date: 2021-03-03
modified: 2023-04-05
tags:
    - attack.execution
    - attack.t1059.001
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
    selection_cli:
        CommandLine|contains|all:
            - ' Net.Sockets.TCPClient'
            - '.GetStream('
            - '.Write('
    condition: all of selection_*
falsepositives:
    - In rare administrative cases, this function might be used to check network connectivity
level: high

[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

a4ce7ff5-5297-41f1-b638-cc763efbe1a6

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Executable code, not a declarative rule

This submission is arbitrary [[ currentRule.format ? currentRule.format.toUpperCase() : '' ]] code, not a declarative detection rule — review it as you would any script before running it, and note that it cannot be safely aggregated or auto-executed alongside YARA/Sigma/Suricata/CRS rules.

Rejected pattern present

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Format & documentation suggestions

Not a security issue — this rule is valid and was accepted as-is. These are optional fields/conventions its own format recommends, mainly affecting its quality score and how well it documents itself for other reviewers.

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[[ currentRule.title && currentRule.title.length > 60 ? currentRule.title.slice(0, 60) + '…' : currentRule.title ]]

[[ currentRule.title ]]

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