Suspicious Vsls-Agent Command With AgentExtensionPath Load

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: bohops
Source: github.com/SigmaHQ/sigma

Detects Microsoft Visual Studio vsls-agent.exe lolbin execution with a suspicious library load using the --agentExtensionPath parameter

Known false positives

False positives depend on custom use of vsls-agent.exe

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218` System Binary Proxy Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: Suspicious Vsls-Agent Command With AgentExtensionPath Load
id: 43103702-5886-11ed-9b6a-0242ac120002
status: test
description: Detects Microsoft Visual Studio vsls-agent.exe lolbin execution with a suspicious library load using the --agentExtensionPath parameter
references:
    - https://twitter.com/bohops/status/1583916360404729857
author: bohops
date: 2022-10-30
tags:
    - attack.stealth
    - attack.t1218
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\vsls-agent.exe'
        CommandLine|contains: '--agentExtensionPath'
    filter:
        CommandLine|contains: 'Microsoft.VisualStudio.LiveShare.Agent.'
    condition: selection and not filter
falsepositives:
    - False positives depend on custom use of vsls-agent.exe
level: medium

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    Image|endswith: '\vsls-agent.exe'
    CommandLine|contains: '--agentExtensionPath'

Stage 2: `not filter`

filter:
    CommandLine|contains: 'Microsoft.VisualStudio.LiveShare.Agent.'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`CommandLine`	match	`Microsoft.VisualStudio.LiveShare.Agent.`	`excludes:CommandLine` `field:"CommandLine" value:"Microsoft.VisualStudio.LiveShare.Agent."`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`--agentExtensionPath`	`field:"CommandLine" kind:match value:"--agentExtensionPath"`
`Image`	ends_with	`\vsls-agent.exe`	`field:"Image" kind:ends_with value:"\vsls-agent.exe"`