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Detection rules › Sigma

ProxyLogon MSExchange OabVirtualDirectory

Status
test
Severity
critical
Log source
product windows, service msexchange-management
Author
Florian Roth (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects specific patterns found after a successful ProxyLogon exploitation in relation to a Commandlet invocation of Set-OabVirtualDirectory

Known false positives

  • Unlikely

MITRE ATT&CK coverage

TacticTechniques
Resource Development

Rule body

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

Stages and Predicates

Stage 0: condition

keywords_cmdlet and keywords_params

Stage 1: keywords_cmdlet

keywords_cmdlet:
    '|all':
        - 'OabVirtualDirectory'
        - ' -ExternalUrl '

Stage 2: keywords_params

keywords_params:
    - 'eval(request'
    - 'http://f/<script'
    - '"unsafe"};'
    - 'function Page_Load()'