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Detection rules › Sigma

UNC4841 - Download Tar File From Untrusted Direct IP Via Wget

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

Detects execution of "wget" to download a "tar" from an IP address that doesn't have a trusted certificate. As seen used by UNC4841 during their Barracuda ESG zero day exploitation.

MITRE ATT&CK coverage

TacticTechniques
StealthT1140 Deobfuscate/Decode Files or Information

Event coverage

ProviderEvent
Sysmon-for-LinuxEvent ID 1

Rule body yaml

title: UNC4841 - Download Tar File From Untrusted Direct IP Via Wget
id: 23835beb-ec38-4e74-a5d4-b99af6684e91
status: test
description: Detects execution of "wget" to download a "tar" from an IP address that doesn't have a trusted certificate. As seen used by UNC4841 during their Barracuda ESG zero day exploitation.
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: '/wget'
        CommandLine|re: 'https://[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
        CommandLine|contains: '--no-check-certificate'
        CommandLine|endswith: '.tar'
    filter_main_local_ips:
        # Note: Uncomment this filter if you want to exclude local IPs
        CommandLine|contains:
            - 'https://10.' # 10.0.0.0/8
            - 'https://192.168.' # 192.168.0.0/16
            - 'https://172.16.' # 172.16.0.0/12
            - 'https://172.17.'
            - 'https://172.18.'
            - 'https://172.19.'
            - 'https://172.20.'
            - 'https://172.21.'
            - 'https://172.22.'
            - 'https://172.23.'
            - 'https://172.24.'
            - 'https://172.25.'
            - 'https://172.26.'
            - 'https://172.27.'
            - 'https://172.28.'
            - 'https://172.29.'
            - 'https://172.30.'
            - 'https://172.31.'
            - 'https://127.' # 127.0.0.0/8
            - 'https://169.254.' # 169.254.0.0/16
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_main_*

Stage 1: selection

selection:
    Image|endswith: '/wget'
    CommandLine|re: 'https://[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}'
    CommandLine|contains: '--no-check-certificate'
    CommandLine|endswith: '.tar'

Stage 2: not filter_main_local_ips

filter_main_local_ips:
    CommandLine|contains:
        - 'https://10.'
        - 'https://192.168.'
        - 'https://172.16.'
        - 'https://172.17.'
        - 'https://172.18.'
        - 'https://172.19.'
        - 'https://172.20.'
        - 'https://172.21.'
        - 'https://172.22.'
        - 'https://172.23.'
        - 'https://172.24.'
        - 'https://172.25.'
        - 'https://172.26.'
        - 'https://172.27.'
        - 'https://172.28.'
        - 'https://172.29.'
        - 'https://172.30.'
        - 'https://172.31.'
        - 'https://127.'
        - 'https://169.254.'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
CommandLinematchhttps://10.
CommandLinematchhttps://127.
CommandLinematchhttps://169.254.
CommandLinematchhttps://172.16.
CommandLinematchhttps://172.17.
CommandLinematchhttps://172.18.
CommandLinematchhttps://172.19.
CommandLinematchhttps://172.20.
CommandLinematchhttps://172.21.
CommandLinematchhttps://172.22.
CommandLinematchhttps://172.23.
CommandLinematchhttps://172.24.
CommandLinematchhttps://172.25.
CommandLinematchhttps://172.26.
CommandLinematchhttps://172.27.
CommandLinematchhttps://172.28.
CommandLinematchhttps://172.29.
CommandLinematchhttps://172.30.
CommandLinematchhttps://172.31.
CommandLinematchhttps://192.168.

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
CommandLineends_with
  • .tar
CommandLinematch
  • --no-check-certificate
CommandLineregex_match
  • https://[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}.[0-9]{1,3}
Imageends_with
  • /wget