RegAsm.EXE Initiating Network Connection To Public IP

Hunt Hypothesis

Detects “RegAsm.exe” initiating a network connection to public IP adresses

Detection Rule

Sigma (Original)

title: RegAsm.EXE Initiating Network Connection To Public IP
id: 0531e43a-d77d-47c2-b89f-5fe50321c805
status: test
description: Detects "RegAsm.exe" initiating a network connection to public IP adresses
references:
    - https://app.any.run/tasks/ec207948-4916-47eb-a0f4-4c6abb2e7668/
    - https://research.splunk.com/endpoint/07921114-6db4-4e2e-ae58-3ea8a52ae93f/
    - https://lolbas-project.github.io/lolbas/Binaries/Regasm/
author: frack113
date: 2024-04-25
tags:
    - attack.stealth
    - attack.t1218.009
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        Initiated: 'true'
        Image|endswith: '\regasm.exe'
    filter_main_local_ranges:
        DestinationIp|cidr:
            - '127.0.0.0/8'
            - '10.0.0.0/8'
            - '172.16.0.0/12'
            - '192.168.0.0/16'
            - '169.254.0.0/16'
            - '::1/128'  # IPv6 loopback
            - 'fe80::/10'  # IPv6 link-local addresses
            - 'fc00::/7'  # IPv6 private addresses
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
level: medium

KQL (Azure Sentinel)

imNetworkSession
| where (NetworkDirection =~ "true" and (SrcProcessName endswith "\\regasm.exe" or DstProcessName endswith "\\regasm.exe")) and (not((ipv4_is_in_range(DstIpAddr, "127.0.0.0/8") or ipv4_is_in_range(DstIpAddr, "10.0.0.0/8") or ipv4_is_in_range(DstIpAddr, "172.16.0.0/12") or ipv4_is_in_range(DstIpAddr, "192.168.0.0/16") or ipv4_is_in_range(DstIpAddr, "169.254.0.0/16") or ipv4_is_in_range(DstIpAddr, "::1/128") or ipv4_is_in_range(DstIpAddr, "fe80::/10") or ipv4_is_in_range(DstIpAddr, "fc00::/7"))))

Required Data Sources

False Positive Guidance

• Unknown

MITRE ATT&CK Context

• Technique: T1218.009 — T1218.009

References

• https://app.any.run/tasks/ec207948-4916-47eb-a0f4-4c6abb2e7668/
• https://research.splunk.com/endpoint/07921114-6db4-4e2e-ae58-3ea8a52ae93f/
• https://lolbas-project.github.io/lolbas/Binaries/Regasm/
• SigmaHQ Rule