Detectionlowtest

Change Default File Association Via Assoc

Detects file association changes using the builtin "assoc" command. When a file is opened, the default program used to open the file (also called the file association or handler) is checked. File association selections are stored in the Windows Registry and can be edited by users, administrators, or programs that have Registry access or by administrators using the built-in assoc utility. Applications can modify the file association for a given file extension to call an arbitrary program when a file with the given extension is opened.

Convert In Phoenix Studio

Open this Sigma rule in the converter with the YAML preloaded and ready for backend selection.

Launch
Timur Zinniatullin, oscd.communityCreated Mon Oct 21Updated Mon Mar 063d3aa6cd-6272-44d6-8afc-7e88dfef7061windows
Log Source
WindowsProcess Creation
ProductWindows← raw: windows
CategoryProcess Creation← raw: process_creation

Events generated when a new process is spawned on the system. Covers command-line arguments, parent/child relationships, and process metadata.

Detection Logic
Detection Logic2 selectors
detection:
    selection_img:
        - Image|endswith: '\cmd.exe'
        - OriginalFileName: 'Cmd.Exe'
    selection_cli:
        CommandLine|contains: 'assoc'
    condition: all of selection_*
False Positives

Admin activity

Testing & Validation

Regression Tests

by SigmaHQ Team
Positive Detection Test1 matchevtx

Microsoft-Windows-Sysmon