Detect Internal Spearphishing in Sumo Logic CSE
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/
Sumo Detection Query
// Signal 1: Outlook macro child process execution
(_sourceCategory="windows/sysmon" OR _sourceCategory="endpoint/windows/process")
| where EventID = "1"
| parse field=ParentImage "*\\*" as parentDir, parentBin nodrop
| where parentBin = "outlook.exe"
| parse field=Image "*\\*" as procDir, procBin nodrop
| where procBin in ("cmd.exe", "powershell.exe", "pwsh.exe", "wscript.exe",
"cscript.exe", "mshta.exe", "rundll32.exe", "regsvr32.exe",
"certutil.exe", "bitsadmin.exe", "msiexec.exe", "wmic.exe",
"curl.exe", "wget.exe")
| fields _messageTime, Computer, User, procBin, CommandLine, ParentImage, ParentCommandLine
| concat("OutlookMacroChildProcess: ", procBin, " | ", CommandLine) as signal_detail
// Signal 2: High-volume internal email send (run as separate search against O365 source)
// (_sourceCategory="o365" OR _sourceCategory="microsoft/o365")
// | json field=_raw "Operation", "UserId", "ClientIP" nodrop
// | where Operation = "Send"
// | where !(UserId matches "*#EXT#*")
// | parse field=UserId "*@*" as localPart, senderDomain
// | timeslice 1h
// | count as EmailsSent, dcount(ClientIP) as UniqueIPs by UserId, senderDomain, _timeslice
// | where EmailsSent > 20
// | concat("HighVolumeInternalSend: ", UserId, " sent ", EmailsSent, " in 1h") as signal_detail
// Signal 3: Teams suspicious link delivery
// (_sourceCategory="o365" OR _sourceCategory="microsoft/teams")
// | json field=_raw "Operation", "UserId", "ExtraProperties" nodrop
// | where Operation in ("MessageCreatedHasLink", "MessageUpdatedHasLink")
// | where ExtraProperties matches "(?i)(https?://|\.(?:zip|exe|lnk|iso|vbs|js|hta|bat|ps1))"
// | where !(ExtraProperties matches "(?i)(microsoft\.com|sharepoint\.com|teams\.microsoft\.com)")
// | concat("TeamsSuspiciousLink: ", UserId, " | ", ExtraProperties) as signal_detail
| count as EventCount by Computer, User, signal_detail
| sort by EventCount descSumo Logic CSE detection for T1534 internal spearphishing across three signals. Signal 1 (primary) matches Sysmon Event ID 1 where outlook.exe spawns known LOLBin processes, indicating VBA macro execution from an internal phishing email. Signals 2 and 3 (commented, run separately against O365 index) detect high-volume send behavior from compromised internal mailboxes and Teams-delivered suspicious links respectively.
Data Sources
Required Tables
False Positives & Tuning
- Outlook integrated workflows using VBScript or PowerShell for legitimate business automation (e.g., IT service desk macros, automated reporting pipelines initiated from Outlook).
- Mass internal communications during corporate events such as earnings announcements, RIF notifications, or all-staff policy changes sent from executive or HR shared mailboxes.
- Microsoft Teams bots or integration webhooks that post links to external file storage (Box, Dropbox, GitHub) may match the suspicious link pattern if the domain is not in the allowlist.
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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