Sigma rule: Suspicious File Created in Outlook Temporary Directory

Rule

Title

Suspicious File Created in Outlook Temporary Directory

Status

experimental

Level

high

Author

Florian Roth (Nextron Systems), Swachchhanda Shrawan Poudel (Nextron Systems)

Date

2025-07-22

File

rules/windows/file/file_event/file_event_win_office_outlook_susp_file_creation_in_temp_dir.yml

Commit

ccbb0369507f796db0b0ae6854c8a2be471b9d84

Detects the creation of files with suspicious file extensions in the temporary directory that Outlook uses when opening attachments.
This can be used to detect spear-phishing campaigns that use suspicious files as attachments, which may contain malicious code.

Log source

product

windows

category

file_event

Detection

selection_extension:
    TargetFilename|endswith:
        - '.cpl'
        - '.hta'
        - '.iso'
        - '.rdp'
        - '.svg'
        - '.vba'
        - '.vbe'
        - '.vbs'
selection_location:
    - TargetFilename|contains:
          - '\AppData\Local\Packages\Microsoft.Outlook_'
          - '\AppData\Local\Microsoft\Olk\Attachments\'
    - TargetFilename|contains|all:
          - '\AppData\Local\Microsoft\Windows\'
          - '\Content.Outlook\'
condition: all of selection_*

False positives (as the rule lists them)

• Opening of headers or footers in email signatures that include SVG images or legitimate SVG attachments

Tags

• attack.initial-access
• attack.t1566.001

MITRE ATT&CK ids this rule names

• T1566.001

Related rules

• f748c45a-f8d3-4e6f-b617-fe176f695b8f (obsolete)

References

• https://vipre.com/blog/svg-phishing-attacks-the-new-trick-in-the-cybercriminals-playbook/
• https://thecyberexpress.com/rogue-rdp-files-used-in-ukraine-cyberattacks/
• https://www.microsoft.com/en-us/security/blog/2024/10/29/midnight-blizzard-conducts-large-scale-spear-phishing-campaign-using-rdp-files/

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