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Detection rules › Sigma

RegAsm.EXE Initiating Network Connection To Public IP

Status
test
Severity
medium
Log source
category network_connection, product windows
Author
frack113
Source
github.com/SigmaHQ/sigma

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

MITRE ATT&CK coverage

TacticTechniques
Stealth

Telemetry coverage

ProviderRecord / event type
SysmonEvent ID 3: Network connection

Rule body

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

Stages and Predicates

Stage 0: condition

selection and not 1 of filter_main_*

Stage 1: selection

selection:
    Initiated: 'true'
    Image|endswith: '\regasm.exe'

Stage 2: not filter_main_local_ranges

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'
        - 'fe80::/10'
        - 'fc00::/7'

Exclusions

The rule actively suppresses these predicates.

FieldKindExcluded valuesSearch
DestinationIpcidr_match10.0.0.0/8excludes:DestinationIp field:"DestinationIp" value:"10.0.0.0/8"
DestinationIpcidr_match127.0.0.0/8excludes:DestinationIp field:"DestinationIp" value:"127.0.0.0/8"
DestinationIpcidr_match169.254.0.0/16excludes:DestinationIp field:"DestinationIp" value:"169.254.0.0/16"
DestinationIpcidr_match172.16.0.0/12excludes:DestinationIp field:"DestinationIp" value:"172.16.0.0/12"
DestinationIpcidr_match192.168.0.0/16excludes:DestinationIp field:"DestinationIp" value:"192.168.0.0/16"
DestinationIpcidr_match::1/128excludes:DestinationIp field:"DestinationIp" value:"::1/128"
DestinationIpcidr_matchfc00::/7excludes:DestinationIp field:"DestinationIp" value:"fc00::/7"
DestinationIpcidr_matchfe80::/10excludes:DestinationIp field:"DestinationIp" value:"fe80::/10"

Indicators

These rows show field, operator, and value matches.

FieldKindValuesSearch
Imageends_with
  • \regasm.exe corpus 9 (sigma 9)
field:"Image" kind:ends_with value:"\regasm.exe"
Initiatedeq
  • true corpus 50 (sigma 50)
field:"Initiated" kind:eq value:"true"