Detect Local Email Collection in Elastic Security
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/
Elastic Detection Query
sequence by host.name with maxspan=5m
[file where event.action in ("creation", "overwrite", "rename") and
(file.name like~ "*.pst" or file.name like~ "*.ost") and
not (
file.path like~ "*\\AppData\\Local\\Microsoft\\Outlook\\*" or
file.path like~ "*\\Documents\\Outlook Files\\*"
)
] by process.entity_id
| [process where event.type == "start" and
(process.name like~ "*.exe") and
not process.name in~ ("outlook.exe", "msoia.exe", "ocpubmgr.exe", "olk.exe",
"searchindexer.exe", "searchprotocolhost.exe", "msosync.exe")
] by process.entity_id
/* Standalone: non-Outlook process accessing PST/OST in Outlook directories */
OR
file where event.action in ("creation", "overwrite", "rename", "access") and
(file.name like~ "*.pst" or file.name like~ "*.ost") and
(
file.path like~ "*\\AppData\\Local\\Microsoft\\Outlook\\*" or
file.path like~ "*\\Documents\\Outlook Files\\*"
) and
not process.name in~ ("outlook.exe", "msoia.exe", "ocpubmgr.exe", "olk.exe",
"searchindexer.exe", "searchprotocolhost.exe", "msosync.exe")
/* Process command-line referencing PST/OST with copy operations */
OR
process where event.type == "start" and
process.name in~ ("cmd.exe", "powershell.exe", "pwsh.exe", "xcopy.exe",
"robocopy.exe", "wmic.exe", "forfiles.exe") and
(
process.args like~ "*.pst*" or process.args like~ "*.ost*" or
process.command_line like~ "*.pst*" or process.command_line like~ "*.ost*"
) and
(
process.command_line like~ "* copy *" or process.command_line like~ "*xcopy*" or
process.command_line like~ "*robocopy*" or process.command_line like~ "*Compress-Archive*" or
process.command_line like~ "*Invoke-WebRequest*" or process.command_line like~ "*curl*"
)Detects local email collection targeting Outlook PST/OST files via three branches: (1) non-Outlook processes accessing email stores in Outlook directories, (2) PST/OST files staged outside normal Outlook paths, and (3) command-line copy/exfiltration operations referencing PST/OST file paths. Covers APT1, QakBot, Carbanak, and RedCurl TTPs for T1114.001.
Data Sources
Required Tables
False Positives & Tuning
- Backup software (e.g., Veeam, Acronis, Windows Backup) legitimately copies PST/OST files during scheduled backup jobs — verify process ancestry and destination path against known backup schedules
- IT administrators using robocopy or xcopy during migration projects (e.g., Office 365 migration) to stage PST files for upload — correlate with change tickets and source IP
- Third-party email archiving or compliance tools (e.g., Mimecast, Veritas Enterprise Vault) that access Outlook data files as part of their normal archiving operations — whitelist known service account names
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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