UNC4841 - SSL Certificate Exfiltration Via Openssl

Status: test
Severity: high
Log source: category process_creation, product linux
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects the execution of "openssl" to connect to an IP address. This techniques was used by UNC4841 to exfiltrate SSL certificates and as a C2 channel with named pipes. Investigate commands executed in the temporal vicinity of this command.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1140` Deobfuscate/Decode Files or Information

Telemetry coverage

Platform	Record / event type
Linux	Event ID 1: Process Create

Rule body

title: UNC4841 - SSL Certificate Exfiltration Via Openssl
id: 60911c07-f989-4362-84af-c609828ef829
status: test
description: Detects the execution of "openssl" to connect to an IP address. This techniques was used by UNC4841 to exfiltrate SSL certificates and as a C2 channel with named pipes. Investigate commands executed in the temporal vicinity of this command.
references:
    - https://www.mandiant.com/resources/blog/barracuda-esg-exploited-globally
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-06-16
tags:
    - attack.stealth
    - attack.t1140
    - detection.emerging-threats
logsource:
    product: linux
    category: process_creation
detection:
    selection:
        Image|endswith: '/openssl'
        CommandLine|re: '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
        CommandLine|contains|all:
            - 's_client'
            - '-quiet'
            - '-connect'
        CommandLine|contains:
            - ':443'
            - ':8080'
    condition: selection
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    Image|endswith: '/openssl'
    CommandLine|re: '[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
    CommandLine|contains|all:
        - 's_client'
        - '-quiet'
        - '-connect'
    CommandLine|contains:
        - ':443'
        - ':8080'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`-connect` `-quiet` `:443` `:8080` `s_client`	`field:"CommandLine" kind:match`
`CommandLine`	regex_match	`[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}`	`field:"CommandLine" kind:regex_match value:"[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}"`
`Image`	ends_with	`/openssl`	`field:"Image" kind:ends_with value:"/openssl"`