Potential Persistence Via Custom Protocol Handler

Hunt Hypothesis

Detects potential persistence activity via the registering of a new custom protocole handlers. While legitimate applications register protocole handlers often times during installation. And attacker c

Detection Rule

Sigma (Original)

title: Potential Persistence Via Custom Protocol Handler
id: fdbf0b9d-0182-4c43-893b-a1eaab92d085
status: test
description: Detects potential persistence activity via the registering of a new custom protocole handlers. While legitimate applications register protocole handlers often times during installation. And attacker can abuse this by setting a custom handler to be used as a persistence mechanism.
references:
    - https://ladydebug.com/blog/2019/06/21/custom-protocol-handler-cph/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2022-05-30
modified: 2023-05-12
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1112
logsource:
    category: registry_set
    product: windows
detection:
    selection:
        TargetObject|startswith: 'HKCR\'
        Details|startswith: 'URL:'
    filter_main_ms_trusted:
        Details|startswith: 'URL:ms-' # Microsoft Protocols usually start with "ms-"
    filter_main_generic_locations:
        Image|startswith: # Add more folders to avoid FP
            - 'C:\Program Files (x86)'
            - 'C:\Program Files\'
            - 'C:\Windows\System32\'
            - 'C:\Windows\SysWOW64\'
    # Uncomment This section to add specific Protocol Handler names that are know
    # filter_specific:
    #     Details: 'URL:'
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Many legitimate applications can register a new custom protocol handler. Additional filters needs to applied according to your environment.
level: medium

KQL (Azure Sentinel)

imRegistry
| where (RegistryKey =~ "HKEY_LOCAL_MACHINE\\CLASSES*" and RegistryValueData startswith "URL:") and (not((RegistryValueData startswith "URL:ms-" or (ActingProcessName startswith "C:\\Program Files (x86)" or ActingProcessName startswith "C:\\Program Files\\" or ActingProcessName startswith "C:\\Windows\\System32\\" or ActingProcessName startswith "C:\\Windows\\SysWOW64\\"))))

Required Data Sources

False Positive Guidance

• Many legitimate applications can register a new custom protocol handler. Additional filters needs to applied according to your environment.

MITRE ATT&CK Context

• Tactic: Persistence
• Technique: T1112 — T1112

References

• https://ladydebug.com/blog/2019/06/21/custom-protocol-handler-cph/
• SigmaHQ Rule