Suspicious Process Access via Direct System Call

Elastic Stack Serverless Security

Identifies suspicious process access events from an unknown memory region. Endpoint security solutions usually hook userland Windows APIs in order to decide if the code that is being executed is malicious or not. It’s possible to bypass hooked functions by writing malicious functions that call syscalls directly.

Rule type: eql

Rule indices:

• winlogbeat-*
• logs-windows.*

Severity: high

Risk score: 73

Runs every: 5m

Searches indices from: now-9m (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

• https://twitter.com/SBousseaden/status/1278013896440324096
• https://www.ired.team/offensive-security/defense-evasion/using-syscalls-directly-from-visual-studio-to-bypass-avs-edrs

Tags:

• Elastic
• Host
• Windows
• Threat Detection
• Defense Evasion

Version: 3

Rule authors:

• Elastic

Rule license: Elastic License v2

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define event.ingested and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate event.ingested to @timestamp for this rule to work.

process where event.code == "10" and
 length(winlog.event_data.CallTrace) > 0 and

 /* Sysmon CallTrace starting with unknown memory module instead of ntdll which host Windows NT Syscalls */
 not winlog.event_data.CallTrace : ("?:\\WINDOWS\\SYSTEM32\\ntdll.dll*", "?:\\WINDOWS\\SysWOW64\\ntdll.dll*")

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Defense Evasion
  • ID: TA0005
  • Reference URL: https://attack.mitre.org/tactics/TA0005/

• Technique:

  • Name: Process Injection
  • ID: T1055
  • Reference URL: https://attack.mitre.org/techniques/T1055/