New Root Certificate Installed Via CertMgr.EXE

Status: test
Severity: medium
Log source: category process_creation, product windows
Author: oscd.community, @redcanary, Zach Stanford @svch0st
Source: github.com/SigmaHQ/sigma

Detects execution of "certmgr" with the "add" flag in order to install a new certificate on the system. Adversaries may install a root certificate on a compromised system to avoid warnings when connecting to adversary controlled web servers.

Known false positives

Help Desk or IT may need to manually add a corporate Root CA on occasion. Need to test if GPO push doesn't trigger FP

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	`T1553.004` Subvert Trust Controls: Install Root Certificate

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: New Root Certificate Installed Via CertMgr.EXE
id: ff992eac-6449-4c60-8c1d-91c9722a1d48
related:
    - id: 42821614-9264-4761-acfc-5772c3286f76
      type: derived
    - id: 46591fae-7a4c-46ea-aec3-dff5e6d785dc
      type: obsolete
status: test
description: |
    Detects execution of "certmgr" with the "add" flag in order to install a new certificate on the system.
    Adversaries may install a root certificate on a compromised system to avoid warnings when connecting to adversary controlled web servers.
references:
    - https://github.com/redcanaryco/atomic-red-team/blob/f339e7da7d05f6057fdfcdd3742bfcf365fee2a9/atomics/T1553.004/T1553.004.md
    - https://securelist.com/to-crypt-or-to-mine-that-is-the-question/86307/
author: oscd.community, @redcanary, Zach Stanford @svch0st
date: 2023-03-05
tags:
    - attack.defense-impairment
    - attack.t1553.004
logsource:
    category: process_creation
    product: windows
detection:
    # Example: CertMgr.exe /add CertificateFileName.cer /s /r localMachine root /all
    selection_img:
        - Image|endswith: '\CertMgr.exe'
        - OriginalFileName: 'CERTMGT.EXE'
    selection_cli:
        CommandLine|contains|all:
            - '/add'
            - 'root'
    condition: all of selection_*
falsepositives:
    - Help Desk or IT may need to manually add a corporate Root CA on occasion. Need to test if GPO push doesn't trigger FP
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\CertMgr.exe'
    - OriginalFileName: 'CERTMGT.EXE'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains|all:
        - '/add'
        - 'root'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`/add` corpus 9 (sigma 5, splunk 2, kusto 2) `root` corpus 3 (sigma 2, splunk 1)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\CertMgr.exe`	`field:"Image" kind:ends_with value:"\CertMgr.exe"`
`OriginalFileName`	eq	`CERTMGT.EXE`	`field:"OriginalFileName" kind:eq value:"CERTMGT.EXE"`