Agent-Skills.md

Agent Skills: Detecting Evasion Techniques in Endpoint Logs

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UncategorizedID: plurigrid/asi/detecting-evasion-techniques-in-endpoint-logs

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plurigrid/asi
plurigridLicense: MIT
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Skill Metadata

Name
detecting-evasion-techniques-in-endpoint-logs
Description
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Detecting Evasion Techniques in Endpoint Logs

When to Use

Use this skill when:

  • Hunting for adversary defense evasion techniques (MITRE ATT&CK TA0005) in endpoint telemetry
  • Building detection rules for common evasion methods (process injection, timestomping, log clearing)
  • Investigating incidents where adversaries disabled or bypassed security tools
  • Analyzing endpoint logs for indicators of living-off-the-land binary (LOLBin) abuse

Do not use this skill for network-level evasion (use network traffic analysis) or for malware reverse engineering.

Prerequisites

  • Sysmon installed and configured with comprehensive logging rules (SwiftOnSecurity or Olaf Hartong config)
  • Windows Security Event Log with advanced audit policy enabled
  • EDR telemetry (CrowdStrike, SentinelOne, Microsoft Defender for Endpoint)
  • SIEM platform for log correlation (Splunk, Elastic, Sentinel)
  • MITRE ATT&CK Enterprise matrix for technique reference

Workflow

Step 1: Detect Log Tampering (T1070)

Windows Event Log clearing (T1070.001):

# Sysmon Event ID 1 (Process Create) for wevtutil
EventID: 1
CommandLine contains: "wevtutil cl" OR "wevtutil clear-log"

# Security Event ID 1102 - Audit log was cleared
EventID: 1102
Source: Microsoft-Windows-Eventlog

# System Event ID 104 - Event log was cleared
EventID: 104

# PowerShell log clearing
EventID: 1 (Sysmon)
CommandLine contains: "Clear-EventLog" OR "Remove-EventLog"

# Splunk query:
index=windows (EventCode=1102 OR EventCode=104)
  OR (EventCode=1 CommandLine="*wevtutil*cl*")
  OR (EventCode=1 CommandLine="*Clear-EventLog*")
| table _time host user CommandLine EventCode

Timestomping (T1070.006):

# Sysmon Event ID 2 - File creation time changed
EventID: 2
# Look for creation times set far in the past on recently-written files
# Correlate with Event ID 11 (FileCreate) - if FileCreate is recent but
# creation time in Event ID 2 is old, timestomping is likely

# MDE Advanced Hunting (KQL):
DeviceFileEvents
| where ActionType == "FileTimestampModified"
| where Timestamp > ago(7d)
| extend TimeDiff = datetime_diff('day', Timestamp, ReportedFileCreationTime)
| where TimeDiff > 30
| project Timestamp, DeviceName, FileName, FolderPath,
    ReportedFileCreationTime, InitiatingProcessFileName

Step 2: Detect Process Injection (T1055)

# Sysmon Event ID 8 - CreateRemoteThread
EventID: 8
# Alert when source process is unusual (not system processes)
# Filter out known legitimate: antivirus, debugging tools
SourceImage NOT IN ("C:\Windows\System32\csrss.exe",
                     "C:\Windows\System32\lsass.exe")

# Sysmon Event ID 10 - ProcessAccess with suspicious access masks
EventID: 10
GrantedAccess contains: "0x1F0FFF" OR "0x1FFFFF" OR "0x001F0FFF"
# PROCESS_ALL_ACCESS = 0x1F0FFF (common in injection)
# Filter legitimate: AV accessing all processes

# Sysmon Event ID 25 - Process Tampering
EventID: 25
Type: "Image is replaced"  # Process hollowing indicator

# Splunk detection:
index=sysmon EventCode=8
| where NOT match(SourceImage, "(?i)(csrss|svchost|MsMpEng|defender)")
| stats count by SourceImage TargetImage host
| where count < 5
| sort - count

Step 3: Detect Security Tool Disabling (T1562)

# Service stopped events for security services
EventID: 7045 (new service) OR 7036 (service state change)
ServiceName IN ("WinDefend", "Sense", "CrowdStrike Falcon Sensor",
                 "SentinelAgent", "csagent", "MBAMService")

# Sysmon Event ID 1 - Processes that disable Defender
CommandLine contains: "Set-MpPreference -DisableRealtimeMonitoring"
  OR "sc stop WinDefend"
  OR "sc config WinDefend start= disabled"
  OR "net stop" AND ("windefend" OR "sense" OR "csagent")

# Registry modification to disable security features
# Sysmon Event ID 13 - Registry value set
TargetObject contains: "DisableAntiSpyware"
  OR "DisableRealtimeMonitoring"
  OR "DisableBehaviorMonitoring"
Details: "DWORD (0x00000001)"

# MDE KQL:
DeviceRegistryEvents
| where RegistryValueName in ("DisableAntiSpyware", "DisableRealtimeMonitoring")
| where RegistryValueData == "1"
| project Timestamp, DeviceName, RegistryKey, InitiatingProcessFileName

Step 4: Detect Masquerading (T1036)

# Sysmon Event ID 1 - Process with legitimate name from unusual path
EventID: 1
Image contains: "svchost.exe" AND Image NOT starts with: "C:\Windows\System32\"
Image contains: "csrss.exe" AND Image NOT starts with: "C:\Windows\System32\"
Image contains: "lsass.exe" AND Image NOT starts with: "C:\Windows\System32\"

# Process name mismatch (original filename vs. current name)
# Sysmon captures OriginalFileName from PE header
EventID: 1
OriginalFileName != (parsed filename from Image path)

# Double extension files
EventID: 11 (FileCreate)
TargetFilename matches: "*\.pdf\.exe" OR "*\.doc\.exe" OR "*\.jpg\.exe"

# Splunk:
index=sysmon EventCode=1
| eval process_name=mvindex(split(Image,"\\"),-1)
| where (process_name="svchost.exe" AND NOT match(Image,"(?i)C:\\\\Windows\\\\System32"))
  OR (process_name="csrss.exe" AND NOT match(Image,"(?i)C:\\\\Windows\\\\System32"))
| table _time host Image ParentImage CommandLine User

Step 5: Detect LOLBin Abuse (T1218, T1127)

# Common LOLBin abuse patterns:

# mshta.exe executing remote content
EventID: 1
Image ends with: "mshta.exe"
CommandLine contains: "http" OR "javascript:" OR "vbscript:"

# certutil.exe downloading files
EventID: 1
Image ends with: "certutil.exe"
CommandLine contains: "-urlcache" OR "-decode" OR "-encode"

# regsvr32.exe executing scriptlets
EventID: 1
Image ends with: "regsvr32.exe"
CommandLine contains: "/s /n /u /i:" OR "scrobj.dll"

# rundll32.exe with unusual DLLs
EventID: 1
Image ends with: "rundll32.exe"
CommandLine contains: "javascript:" OR ".js" OR "http:"

# MSBuild executing inline tasks
EventID: 1
Image contains: "MSBuild.exe"
CommandLine NOT contains: ".sln" AND NOT contains: ".csproj"

Step 6: Build Detection Rule Correlation

# Combine multiple weak signals into high-confidence detection:

# Rule: Potential post-exploitation evasion chain
# Trigger when 3+ evasion techniques observed on same host within 1 hour

# Splunk correlation search:
index=sysmon host=*
| eval technique=case(
    EventCode=2, "timestomping",
    EventCode=8 AND NOT match(SourceImage,"csrss|svchost"), "process_injection",
    EventCode=1 AND match(CommandLine,"(?i)wevtutil.*cl"), "log_clearing",
    EventCode=13 AND match(TargetObject,"DisableRealtimeMonitoring"), "security_disable",
    EventCode=1 AND match(CommandLine,"(?i)(mshta|certutil.*urlcache|regsvr32.*/s.*/n)"), "lolbin_abuse",
    true(), NULL
)
| where isnotnull(technique)
| bin _time span=1h
| stats dc(technique) as technique_count values(technique) as techniques by host _time
| where technique_count >= 3
| sort - technique_count

Key Concepts

| Term | Definition | |------|-----------| | Defense Evasion (TA0005) | MITRE ATT&CK tactic where adversaries attempt to avoid detection during operations | | Process Injection (T1055) | Technique of injecting code into another process's memory space to execute in a trusted context | | Timestomping (T1070.006) | Modifying file timestamps to make malicious files appear old and blend with legitimate files | | Masquerading (T1036) | Naming malicious files or processes to match legitimate system files to avoid detection | | LOLBin | Living Off the Land Binary; legitimate Windows tool repurposed by adversaries | | Indicator Removal (T1070) | Clearing logs, deleting files, or modifying artifacts to remove evidence of compromise |

Tools & Systems

  • Sysmon: Advanced Windows system monitoring with kernel-level visibility
  • Microsoft Defender for Endpoint: EDR with advanced hunting (KQL) for evasion detection
  • CrowdStrike Falcon: IOA-based behavioral detection for evasion techniques
  • Elastic Security: SIEM with prebuilt detection rules for ATT&CK evasion techniques
  • Sigma Rules: Vendor-agnostic detection rule format with extensive evasion rule library

Common Pitfalls

  • Alert fatigue from process injection rules: Many legitimate tools (AV, accessibility) perform process injection. Maintain an allowlist of known-good source processes.
  • Missing Sysmon Event ID 8/10: Default Sysmon configurations may not capture CreateRemoteThread or ProcessAccess. Use a comprehensive Sysmon config.
  • Ignoring parent process context: A suspicious command line from cmd.exe is concerning only if the parent of cmd.exe is unusual (e.g., Excel spawning cmd.exe).
  • Not correlating across event types: Single events are often benign. Combine multiple weak signals (process creation + network connection + file creation) for high-confidence detections.