Detect Local Email Collection in Splunk
Adversaries may target user email on local systems to collect sensitive information. Outlook stores email data in offline data files (.ost) and personal storage table files (.pst), typically located in C:\Users\<username>\AppData\Local\Microsoft\Outlook or C:\Users\<username>\Documents\Outlook Files. Threat actors access, copy, or exfiltrate these files to harvest credentials, reconnaissance data, business intelligence, or email threads for thread-hijacking phishing campaigns. Groups such as APT1, QakBot, Carbanak, and RedCurl have all employed this technique at scale.
MITRE ATT&CK
- Tactic
- Collection
- Technique
- T1114 Email Collection
- Sub-technique
- T1114.001 Local Email Collection
- Canonical reference
- https://attack.mitre.org/techniques/T1114/001/
SPL Detection Query
index=sysmon sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational"
(
(EventCode=11 (TargetFilename="*.pst" OR TargetFilename="*.ost"))
OR
(EventCode=1 (CommandLine="*.pst*" OR CommandLine="*.ost*"))
)
| eval FilePath=coalesce(TargetFilename, "")
| eval CommandLineVal=coalesce(CommandLine, "")
| eval ProcessName=lower(coalesce(Image, ""))
| eval ParentProcessName=lower(coalesce(ParentImage, ""))
| eval IsOutlookPath=if(match(FilePath, "(?i)(AppData\\Local\\Microsoft\\Outlook|Documents\\Outlook Files)"), 1, 0)
| eval IsStagingPath=if(match(FilePath, "(?i)(\\Windows\\Temp|\\Temp\\|\\Downloads\\|\\Public\\|\\ProgramData\\)"), 1, 0)
| eval IsTrustedOutlookProc=if(match(ProcessName, "(outlook\.exe|searchindexer\.exe|searchprotocolhost\.exe|msosync\.exe|ocpubmgr\.exe)"), 1, 0)
| eval IsCopyOp=if(match(CommandLineVal, "(?i)(\bcopy\b|xcopy|robocopy|\bcp\b|move|compress-archive|invoke-webrequest|\bcurl\b|wmic.*process.*call.*create)"), 1, 0)
| eval IsPstOstCmdLine=if(match(CommandLineVal, "(?i)\.(pst|ost)"), 1, 0)
| eval DetectionBranch=case(
EventCode=11 AND IsStagingPath=1, "EmailFileStagedInSuspiciousLocation",
EventCode=11 AND IsTrustedOutlookProc=0, "NonOutlookProcessCreatedEmailFile",
EventCode=1 AND IsPstOstCmdLine=1 AND IsCopyOp=1, "CommandLinePstCopyOperation",
EventCode=1 AND IsPstOstCmdLine=1, "CommandLineReferencingEmailStore",
true(), "Other"
)
| eval RiskScore=case(
IsStagingPath=1 AND IsTrustedOutlookProc=0, 3,
IsCopyOp=1 AND IsPstOstCmdLine=1, 3,
DetectionBranch="NonOutlookProcessCreatedEmailFile", 2,
true(), 1
)
| where DetectionBranch != "Other"
| table _time, host, User, ProcessName, ParentProcessName, CommandLineVal, FilePath,
EventCode, DetectionBranch, RiskScore, IsOutlookPath, IsStagingPath
| sort - RiskScore, - _timeDetects local email collection using Sysmon Event ID 11 (File Create) and Event ID 1 (Process Create). Identifies four detection branches: email files appearing in staging locations (Windows Temp, ProgramData, Downloads), non-Outlook processes creating .pst/.ost files, explicit command-line copy operations referencing email store files, and any command-line reference to .pst/.ost paths. Assigns a RiskScore to prioritize analyst review — score 3 for staging + non-Outlook process combinations or explicit copy operations targeting email stores.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Backup agents (Veeam, Acronis, Windows Backup) accessing Outlook data files during scheduled profile backups — typically identifiable by known parent service processes
- IT PST migration tools used during Exchange Online or M365 transitions that legitimately enumerate and copy .pst files from user workstations
- DLP or antivirus scanning engines that inspect .pst/.ost content and may trigger FileCreate events when extracting or scanning
- Third-party Outlook backup or archiving utilities (MailStore, Stellar, Kernel OST Viewer) that access offline stores as part of their normal operation
Other platforms for T1114.001
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 1Copy Outlook OST File to Windows Temp (cmd.exe)
Expected signal: Sysmon Event ID 1: Process Create with Image=cmd.exe, CommandLine containing '.ost' and 'copy'. Sysmon Event ID 11: File Create with TargetFilename=%TEMP%\staged_email.ost, Image=cmd.exe. Security Event ID 4688 (if process command line auditing enabled) with same details. Security Event ID 4663 (if object access auditing enabled on Outlook directory) showing read access by cmd.exe.
- Test 2Enumerate and Copy PST Files with PowerShell
Expected signal: Sysmon Event ID 1: Process Create with Image=powershell.exe, CommandLine containing 'Get-ChildItem', '.pst', and 'Copy-Item'. Sysmon Event ID 11: File Create with TargetFilename=C:\ProgramData\dftest_email_staged.pst, Image=powershell.exe. PowerShell ScriptBlock Log Event ID 4104 capturing full script. Security Event ID 4688 for the PowerShell process.
- Test 3WMIC Remote Process PST Copy (Chimera APT Pattern)
Expected signal: Sysmon Event ID 1: Process Create with Image=wmic.exe, CommandLine containing 'process call create' and '.ost'. Secondary Sysmon Event ID 1 for the spawned cmd.exe with the copy command. Sysmon Event ID 11 for the created file in Temp. Security Event ID 4688 for both wmic.exe and cmd.exe child process. Sysmon Event ID 3 (Network Connection) for wmic WMI connection to localhost.
- Test 4Archive Outlook Data Files for Exfiltration Preparation
Expected signal: Sysmon Event ID 1: Process Create with Image=powershell.exe, CommandLine containing 'Compress-Archive' and '.pst'. Sysmon Event ID 11: File Create events for both the dummy .pst and the resulting .zip archive in Temp. PowerShell ScriptBlock Log Event ID 4104 with full script. File Create event for the archive file may also trigger DLP rules if archive-in-staging detection is enabled.
References (9)
- https://attack.mitre.org/techniques/T1114/001/
- https://support.office.com/en-us/article/introduction-to-outlook-data-files-pst-and-ost-222eaf92-a995-45d9-bde2-f331f60e2790
- https://practical365.com/clients/office-365-proplus/outlook-cached-mode-ost-file-sizes/
- https://www.mandiant.com/resources/blog/apt1-exposing-one-of-chinas-cyber-espionage-units
- https://blog.talosintelligence.com/2018/07/smoking-guns-smoke-loader-learned-new.html
- https://www.kroll.com/en/insights/publications/cyber/qakbot-malware-growing-threat
- https://www.group-ib.com/resources/threat-research/red-curl.html
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicefileevents-table
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1114.001/T1114.001.md
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