ProxyLogon MSExchange OabVirtualDirectory — Sigma Rule

Rule metadata and linked tags

Author: Florian Roth (Nextron Systems). Source status: test; severity: critical. Source dates: 2021-08-09 / 2023-01-23.

{
  "product": "windows",
  "service": "msexchange-management"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 9705b2f3f28a85e9c3d4d97ac4022c686de433e040ee3151b0c9ec61e7b5cbf3

Detection logic

Original source YAML. Source-tag agreement is not proof of complete semantic coverage. This rule has not been compiled for a SIEM backend or validated against live telemetry here.

title: ProxyLogon MSExchange OabVirtualDirectory
id: 550d3350-bb8a-4ff3-9533-2ba533f4a1c0
status: test
description: Detects specific patterns found after a successful ProxyLogon exploitation in relation to a Commandlet invocation of Set-OabVirtualDirectory
references:
    - https://bi-zone.medium.com/hunting-down-ms-exchange-attacks-part-1-proxylogon-cve-2021-26855-26858-27065-26857-6e885c5f197c
author: Florian Roth (Nextron Systems)
date: 2021-08-09
modified: 2023-01-23
tags:
    - attack.t1587.001
    - attack.resource-development
logsource:
    product: windows
    service: msexchange-management
detection:
    keywords_cmdlet:
        '|all':
            - 'OabVirtualDirectory'
            - ' -ExternalUrl '
    keywords_params:
        - 'eval(request'
        - 'http://f/<script'
        - '"unsafe"};'
        - 'function Page_Load()'
    condition: keywords_cmdlet and keywords_params
falsepositives:
    - Unlikely
level: critical

Original YAML and metadata in JSON

False positives

• Unlikely

Source references

• https://bi-zone.medium.com/hunting-down-ms-exchange-attacks-part-1-proxylogon-cve-2021-26855-26858-27065-26857-6e885c5f197c