Suspicious SSL Connection

Status: test
Severity: low
Log source: category ps_script, product windows
Author: frack113
Source: github.com/SigmaHQ/sigma

Adversaries may employ a known encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol.

Known false positives

Legitimate administrative script

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1573` Encrypted Channel

Telemetry coverage

Provider	Record / event type
PowerShell	Event ID 4104: Creating Scriptblock text (MessageNumber of MessageTotal).

Rule body

title: Suspicious SSL Connection
id: 195626f3-5f1b-4403-93b7-e6cfd4d6a078
status: test
description: Adversaries may employ a known encryption algorithm to conceal command and control traffic rather than relying on any inherent protections provided by a communication protocol.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1573/T1573.md#atomic-test-1---openssl-c2
    - https://medium.com/walmartglobaltech/openssl-server-reverse-shell-from-windows-client-aee2dbfa0926
author: frack113
date: 2022-01-23
tags:
    - attack.command-and-control
    - attack.t1573
logsource:
    product: windows
    category: ps_script
    definition: 'Requirements: Script Block Logging must be enabled'
detection:
    selection:
        ScriptBlockText|contains|all:
            - System.Net.Security.SslStream
            - Net.Security.RemoteCertificateValidationCallback
            - '.AuthenticateAsClient'
    condition: selection
falsepositives:
    - Legitimate administrative script
level: low

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    ScriptBlockText|contains|all:
        - System.Net.Security.SslStream
        - Net.Security.RemoteCertificateValidationCallback
        - '.AuthenticateAsClient'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ScriptBlockText`	match	`.AuthenticateAsClient` `Net.Security.RemoteCertificateValidationCallback` `System.Net.Security.SslStream`	`field:"ScriptBlockText" kind:match`