Sigma rule: Access To Windows Outlook Mail Files By Uncommon Applications

Rule

Title

Access To Windows Outlook Mail Files By Uncommon Applications

Status

test

Level

low

Author

frack113

Date

2024-05-10

Modified

2024-07-29

File

rules-threat-hunting/windows/file/file_access/file_access_win_office_outlook_mail_credential.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects file access requests to Windows Outlook Mail by uncommon processes.
Could indicate potential attempt of credential stealing.
Requires heavy baselining before usage

Log source

product

windows

category

file_access

definition

Requirements: Microsoft-Windows-Kernel-File ETW provider

Detection

selection_unistore:
    FileName|contains: '\AppData\Local\Comms\Unistore\data'
selection_unistoredb:
    FileName|endswith: '\AppData\Local\Comms\UnistoreDB\store.vol'
filter_main_system:
    Image: 'System'
filter_main_generic:
    # This filter is added to avoid large amount of FP with 3rd party software. You should remove this in favour of specific filter per-application
    Image|startswith:
        - 'C:\Program Files (x86)\'
        - 'C:\Program Files\'
        - 'C:\Windows\system32\'
        - 'C:\Windows\SysWOW64\'
filter_optional_defender:
    Image|startswith: 'C:\ProgramData\Microsoft\Windows Defender\'
    Image|endswith:
        - '\MpCopyAccelerator.exe'
        - '\MsMpEng.exe'
filter_optional_thor:
    Image|endswith:
        - '\thor64.exe'
        - '\thor.exe'
condition: 1 of selection_* and not 1 of filter_main_* and not 1 of filter_optional_*

False positives (as the rule lists them)

• Antivirus, Anti-Spyware, Anti-Malware Software
• Backup software
• Legitimate software installed on partitions other than "C:\"
• Searching software such as "everything.exe"

Tags

• attack.stealth
• attack.t1070.008
• detection.threat-hunting

MITRE ATT&CK ids this rule names

• T1070.008

References

• https://darkdefender.medium.com/windows-10-mail-app-forensics-39025f5418d2
• https://github.com/redcanaryco/atomic-red-team/blob/58496ee3306e6e42a7054d36a94e6eb561ee3081/atomics/T1070.008/T1070.008.md#atomic-test-4---copy-and-modify-mailbox-data-on-windows

Read on 2026-11-03T00:58:21.399Z under licence sigma-drl-1.1@d5f4c36a from https://github.com/SigmaHQ/sigma/blob/ccbb0369507f796db0b0ae6854c8a2be471b9d84/rules-threat-hunting/windows/file/file_access/file_access_win_office_outlook_mail_credential.yml