Detect Exploitation for Client Execution in Google Chronicle
Adversaries may exploit software vulnerabilities in client applications to execute code. This includes browser-based exploitation via drive-by compromise or spearphishing links, Office application exploitation through malicious attachments (CVE-2017-11882, CVE-2017-0262, CVE-2021-40444), and third-party application exploitation (Adobe Reader, Flash). These exploits cause vulnerable client software to execute attacker-controlled code, often spawning unexpected child processes or injecting shellcode into memory.
MITRE ATT&CK
- Tactic
- Execution
- Technique
- T1203 Exploitation for Client Execution
- Canonical reference
- https://attack.mitre.org/techniques/T1203/
YARA-L Detection Query
rule t1203_client_exploitation_suspicious_child_spawn {
meta:
author = "Argus Detection Engineering"
description = "Detects T1203 Exploitation for Client Execution via LOLBins or script interpreters spawned by Office apps, browsers, or PDF readers"
severity = "HIGH"
mitre_attack_tactic = "Execution"
mitre_attack_technique = "T1203"
reference = "https://attack.mitre.org/techniques/T1203/"
version = "1.0"
events:
$e.metadata.event_type = "PROCESS_LAUNCH"
re.regex(
$e.principal.process.file.full_path,
`(?i)(winword|excel|powerpnt|outlook|mspub|visio|onenote|msaccess|chrome|firefox|msedge|iexplore|opera|brave|acrord32|acrobat|foxitpdfeditor|sumatrapdf)\.exe$`
)
re.regex(
$e.target.process.file.full_path,
`(?i)(cmd|powershell|pwsh|wscript|cscript|mshta|rundll32|regsvr32|certutil|bitsadmin|msbuild|installutil|regasm|regsvcs|schtasks|wmic|msiexec)\.exe$`
)
$hostname = $e.principal.hostname
condition:
$e
}Chronicle YARA-L 2.0 rule detecting T1203 exploitation using PROCESS_LAUNCH UDM events. Matches principal.process.file.full_path (the spawning parent application) against Office suite, web browser, and PDF reader application regexes, and target.process.file.full_path (the newly created process) against the LOLBin and script interpreter set. The principal/target UDM semantics enforce process lineage so the rule requires the client application to be the direct parent of the suspicious child process. Backtick regex strings in YARA-L are case-insensitive via the (?i) flag.
Data Sources
Required Tables
False Positives & Tuning
- Enterprise IT automation workflows where Office applications invoke PowerShell or cmd.exe via COM automation for managed endpoint deployment scripts, patch management, or inventory collection
- Browser native messaging host integrations for enterprise SSO, hardware security key management, or privileged access management tools that spawn rundll32.exe or msiexec.exe for local middleware communication
- Adobe Acrobat Pro or Foxit enterprise licensing scripts that invoke certutil.exe or wscript.exe during product activation, certificate-based authentication setup, or enterprise policy enforcement on managed desktops
Other platforms for T1203
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate Office Exploitation — Equation Editor Child Process
Expected signal: Sysmon Event ID 1: Process Create with ParentImage containing eqnedt32.exe and Image=cmd.exe. Security Event ID 4688 with similar parent/child relationship if command line auditing enabled.
- Test 2Office Application Spawning PowerShell via Macro Simulation
Expected signal: Sysmon Event ID 1: Process Create chain showing cmd.exe spawning powershell.exe. The detection focuses on the child process spawning pattern. PowerShell ScriptBlock Log Event ID 4104 will record the Write-Output command.
- Test 3Browser Renderer Process Spawning Cmd
Expected signal: Sysmon Event ID 1: Process Create for cmd.exe with subsequent net.exe and whoami.exe child processes. This represents the reconnaissance commands commonly executed immediately following successful browser exploitation.
- Test 4Mshta Spawned from Office Context (CVE-2021-40444 Pattern)
Expected signal: Sysmon Event ID 1: Process Create for mshta.exe. In real exploitation this process would have a parent of winword.exe or excel.exe. Security Event ID 4688 will also record the mshta.exe launch with command line arguments.
References (8)
- https://attack.mitre.org/techniques/T1203/
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2017-11882
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-40444
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1203/T1203.md
- https://www.mandiant.com/resources/blog/evasive-attacker-leverages-solarwinds-supply-chain-compromises-with-sunburst-backdoor
- https://github.com/SigmaHQ/sigma/tree/master/rules/windows/process_creation
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-deviceprocessevents-table
- https://www.sentinelone.com/blog/agent-tesla-old-rat-uses-new-tricks-to-stay-on-top/
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