Obfuscated IP Download Activity

Hunt Hypothesis

Detects use of an encoded/obfuscated version of an IP address (hex, octal…) in an URL combined with a download command

Detection Rule

Sigma (Original)

title: Obfuscated IP Download Activity
id: cb5a2333-56cf-4562-8fcb-22ba1bca728d
status: test
description: Detects use of an encoded/obfuscated version of an IP address (hex, octal...) in an URL combined with a download command
references:
    - https://h.43z.one/ipconverter/
    - https://twitter.com/Yasser_Elsnbary/status/1553804135354564608
    - https://twitter.com/fr0s7_/status/1712780207105404948
author: Florian Roth (Nextron Systems), X__Junior (Nextron Systems)
date: 2022-08-03
modified: 2026-03-16
tags:
    - attack.discovery
logsource:
    category: process_creation
    product: windows
detection:
    selection_command:
        CommandLine|contains:
            - 'Invoke-WebRequest'
            - 'iwr '
            - 'Invoke-RestMethod'
            - 'irm '
            - 'wget '
            - 'curl '
            - 'DownloadFile'
            - 'DownloadString'
    selection_ip_1:
        CommandLine|contains:
            - ' 0x'
            - '//0x'
            - '.0x'
            - '.00x'
    selection_ip_2:
        CommandLine|contains|all:
            - 'http://%'
            - '%2e'
    selection_ip_3:
        # http://81.4.31754
        - CommandLine|re: 'https?://[0-9]{1,3}\.[0-9]{1,3}\.0[0-9]{3,4}'
        # http://81.293898
        - CommandLine|re: 'https?://[0-9]{1,3}\.0[0-9]{3,7}'
        # http://1359248394
        - CommandLine|re: 'https?://0[0-9]{3,11}'
        # http://0121.04.0174.012
        - CommandLine|re: 'https?://(?:0[0-9]{1,11}\.){3}0[0-9]{1,11}'
        # http://012101076012
        - CommandLine|re: 'https?://0[0-9]{1,11}'
        # For octal format
        - CommandLine|re: ' [0-7]{7,13}'
    filter_main_valid_ip:
        CommandLine|re: 'https?://(?:(?:25[0-5]|(?:2[0-4]|1\d|[1-9])?\d)(?:\.|\b)){4}'
    condition: selection_command and 1 of selection_ip_* and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

KQL (Azure Sentinel)

imProcessCreate
| where (TargetProcessCommandLine contains "Invoke-WebRequest" or TargetProcessCommandLine contains "iwr " or TargetProcessCommandLine contains "Invoke-RestMethod" or TargetProcessCommandLine contains "irm " or TargetProcessCommandLine contains "wget " or TargetProcessCommandLine contains "curl " or TargetProcessCommandLine contains "DownloadFile" or TargetProcessCommandLine contains "DownloadString") and ((TargetProcessCommandLine contains " 0x" or TargetProcessCommandLine contains "//0x" or TargetProcessCommandLine contains ".0x" or TargetProcessCommandLine contains ".00x") or (TargetProcessCommandLine contains "http://%" and TargetProcessCommandLine contains "%2e") or (TargetProcessCommandLine matches regex "https?://[0-9]{1,3}\\.[0-9]{1,3}\\.0[0-9]{3,4}" or TargetProcessCommandLine matches regex "https?://[0-9]{1,3}\\.0[0-9]{3,7}" or TargetProcessCommandLine matches regex "https?://0[0-9]{3,11}" or TargetProcessCommandLine matches regex "https?://(?:0[0-9]{1,11}\\.){3}0[0-9]{1,11}" or TargetProcessCommandLine matches regex "https?://0[0-9]{1,11}" or TargetProcessCommandLine matches regex " [0-7]{7,13}")) and (not(TargetProcessCommandLine matches regex "https?://(?:(?:25[0-5]|(?:2[0-4]|1\\d|[1-9])?\\d)(?:\\.|\\b)){4}"))

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Tactic: Discovery

References

• https://h.43z.one/ipconverter/
• https://twitter.com/Yasser_Elsnbary/status/1553804135354564608
• https://twitter.com/fr0s7_/status/1712780207105404948
• SigmaHQ Rule