Detect Internal Spearphishing in CrowdStrike LogScale
Adversaries who have already compromised an account or system may abuse the trusted internal identity to send phishing messages to other users within the same organization. Because the message originates from a known colleague, recipients are far more likely to open attachments, click links, or provide credentials. Campaigns typically combine a compromised mailbox or chat account with a weaponized attachment, a credential-harvesting link, or a malicious macro-enabled document. Real-world actors include Gamaredon (Outlook VBA module auto-sending phishing to contacts), Kimsuky (stolen credentials reused for internal mail), Leviathan/APT40, and HEXANE. Detection surfaces include anomalous send volume or recipient patterns from an internal account, Outlook spawning suspicious child processes (macro execution), Microsoft Teams delivering external URLs or files, and mass-BCC or reply-all abuse patterns.
MITRE ATT&CK
- Tactic
- Lateral Movement
- Technique
- T1534 Internal Spearphishing
- Canonical reference
- https://attack.mitre.org/techniques/T1534/
LogScale Detection Query
// Signal 1: Outlook spawning suspicious child processes (macro execution)
// Uses Falcon ProcessRollup2 events
#event_simpleName = "ProcessRollup2"
| ParentBaseFileName = "outlook.exe"
| FileName = /^(cmd|powershell|pwsh|wscript|cscript|mshta|rundll32|regsvr32|certutil|bitsadmin|msiexec|wmic|curl|wget)\.exe$/i
| table([_time, ComputerName, UserName, FileName, CommandLine, ParentBaseFileName, ParentCommandLine])
| eval Signal = "OutlookMacroChildProcess"
| eval SuspicionScore = 3
// Signal 2: Anomalous process creation burst from Outlook (proxy for mass-send behavior in EDR)
// CrowdStrike does not natively ingest O365 MailSend audit — use Falcon LogScale Connector for O365
// If O365 logs are forwarded to LogScale:
// #type = "o365" event.Operation = "Send"
// | groupBy([UserId, timebucket("1h", _time)], function=count(as=EmailsSent))
// | EmailsSent > 20
// | eval Signal = "HighVolumeInternalSend"
// | eval SuspicionScore = 2
// Signal 3: Network connection from Outlook to non-Microsoft external hosts post-process-spawn
| join(
[
#event_simpleName = "NetworkConnectIP4"
| LocalAddressIP4 != "127.0.0.1"
| not RemoteAddressIP4 = /^(10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.)/
| not RemotePort in [443, 80]
],
field=[TargetProcessId],
include=[RemoteAddressIP4, RemotePort, RemoteAddressIP4]
)
| groupBy([ComputerName, UserName, FileName, Signal], function=count(as=EventCount))
| sort(EventCount, order=desc)CrowdStrike LogScale (Falcon) detection for T1534 internal spearphishing. Signal 1 targets ProcessRollup2 events where outlook.exe is the parent of known LOLBin processes — the primary high-fidelity indicator. An optional join with NetworkConnectIP4 enriches events with external connection attempts immediately after macro execution, increasing fidelity. O365 high-volume send signal requires the Falcon LogScale O365 connector or Cribl pipeline to forward O365 management activity logs into LogScale (commented section).
Data Sources
Required Tables
False Positives & Tuning
- Outlook COM add-ins from enterprise vendors (Zoom, Salesforce, ServiceNow) frequently spawn rundll32.exe or powershell.exe as part of plugin initialization or update checks, generating false ProcessRollup2 matches.
- Automated internal notification workflows where Outlook macros legitimately call cmd.exe or PowerShell to query internal APIs, generate ticket numbers, or populate document templates.
- Security awareness phishing simulation platforms (KnowBe4, Proofpoint Security Awareness) that send internal test phishing emails may trigger the high-volume send signal from simulation accounts if not excluded by sender address pattern.
Other platforms for T1534
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 1Outlook VBA Macro Auto-Send (Simulated Gamaredon Pattern)
Expected signal: Sysmon Event ID 1: powershell.exe spawned with Outlook COM object instantiation. OfficeActivity O365 log: Operation=Send from the test account. If Outlook is running, Sysmon Event ID 10 (ProcessAccess) may show PowerShell accessing the Outlook process. Exchange/O365 message trace will record the outbound message.
- Test 2Write Malicious Macro to Outlook VbaProject.OTM
Expected signal: Sysmon Event ID 11 (File Create): file creation event for the test artifact in %TEMP%. Sysmon Event ID 1: powershell.exe with path references to VbaProject.OTM. If Outlook is running and VbaProject.OTM is actually modified, Sysmon will log file modification events against the OTM path.
- Test 3Microsoft Teams Message with External Link (Simulated via Graph API)
Expected signal: O365 OfficeActivity: RecordType=MicrosoftTeams, Operation=MessageCreatedHasLink, with the external URL in ExtraProperties. Azure AD sign-in log entry for the Graph API token use. Microsoft Defender for Cloud Apps (MCAS) may generate an alert for 'Suspicious inbox forwarding' or 'Unusual file share' depending on policy.
- Test 4Simulate Compromised Account Bulk Send via PowerShell Exchange Online
Expected signal: O365 Unified Audit Log: multiple Send operations from [email protected] within a short window. Exchange message trace: batch of outbound messages with identical subject. Azure AD: interactive authentication event for the PowerShell connection. OfficeActivity table in Sentinel: Operation=Send entries for each recipient.
References (9)
- https://attack.mitre.org/techniques/T1534/
- https://blog.trendmicro.com/phishing-starts-inside/
- https://www.microsoft.com/en-us/security/blog/2023/08/02/midnight-blizzard-conducts-targeted-social-engineering-over-microsoft-teams/
- https://www.welivesecurity.com/2020/06/11/gamaredon-group-grows-its-game/
- https://www.cisa.gov/sites/default/files/publications/AA21-200A.pdf
- https://secureworks.com/research/lyceum-takes-center-stage-in-middle-east-campaign
- https://learn.microsoft.com/en-us/microsoft-365/compliance/audit-log-search-tool
- https://learn.microsoft.com/en-us/defender-office-365/anti-phishing-policies-about
- https://learn.microsoft.com/en-us/microsoftteams/teams-security-guide
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