Detect Local Email Collection in CrowdStrike LogScale
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/
LogScale Detection Query
// Branch 1 & 2: File write/creation events targeting .pst or .ost files
#event_simpleName = "PeFileWritten" OR #event_simpleName = "NewExecutableWritten" OR #event_simpleName = "SuspiciousFileWritten"
| FileName = /(?i)\.(pst|ost)$/
| FilePath != null
| isOutlookPath := match(field=FilePath, pattern=/(AppData\\Local\\Microsoft\\Outlook|Documents\\Outlook Files)/i)
| isStagingPath := match(field=FilePath, pattern=/(\\Windows\\Temp|\\Temp\\|\\Downloads\\|\\Public\\|\\ProgramData\\|\\AppData\\Roaming\\|\\Users\\Public\\)/i)
| isTrustedProc := match(field=ImageFileName, pattern=/(outlook\.exe|msoia\.exe|ocpubmgr\.exe|olk\.exe|searchindexer\.exe|searchprotocolhost\.exe|msosync\.exe)/i)
| where (isOutlookPath = true AND isTrustedProc = false) OR isStagingPath = true
| DetectionBranch := if(isOutlookPath = true AND isTrustedProc = false, "NonOutlookProcessAccessingEmailStore",
if(isStagingPath = true, "EmailFileStagedInSuspiciousLocation", "EmailFileWritten"))
| RiskScore := if(isStagingPath = true AND isTrustedProc = false, 3,
if(DetectionBranch = "NonOutlookProcessAccessingEmailStore", 2, 1))
| table([_timstamp, ComputerName, UserName, FileName, FilePath, ImageFileName,
ParentBaseFileName, DetectionBranch, RiskScore])
// Branch 3: Process execution with PST/OST in command line
| join(
#event_simpleName = "ProcessRollup2"
| ImageFileName = /(?i)(cmd\.exe|powershell\.exe|pwsh\.exe|xcopy\.exe|robocopy\.exe|wmic\.exe|forfiles\.exe)/
| CommandLine = /(?i)\.(pst|ost)/
| isCopyOp := match(field=CommandLine, pattern=/(\bcopy\b|xcopy|robocopy|Compress-Archive|Invoke-WebRequest|\bcurl\b|wmic.*process|\bmove\b)/i)
| where isCopyOp = true
| DetectionBranch := "CommandLinePstCopyOperation"
| RiskScore := 3
| table([_timstamp, ComputerName, UserName, FileName, CommandLine,
ParentBaseFileName, DetectionBranch, RiskScore])
, field=ComputerName, joinType=full
)
| sort(field=RiskScore, order=desc)
| sort(field=_timstamp, order=desc)CrowdStrike LogScale (Falcon) query detecting T1114.001 Local Email Collection using Falcon endpoint telemetry. Monitors PeFileWritten and related file events for PST/OST writes by non-Outlook processes or to staging directories, and ProcessRollup2 events for command-line utilities referencing PST/OST files with copy/exfiltration operations. Leverages native Falcon event schema.
Data Sources
Required Tables
False Positives & Tuning
- CrowdStrike Falcon sensor's own processes or third-party EDR agents that inspect PST/OST files for malware scanning will match Branch 1 — exclude by CID-verified sensor process ImageFileName values
- Corporate PST archival workflows using PowerShell or cmd.exe scheduled tasks for nightly PST compaction or backup — these produce identical Branch 3 signals; correlate CommandLine hash against approved automation script registry
- Network-attached or cloud backup clients (e.g., Backblaze, Carbonite, OneDrive sync client for large PST files) writing PST/OST data to staging areas before upload — verify ImageFileName digital signature publisher field matches expected backup vendor
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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