Potentially Suspicious Azure Front Door Connection

title: Potentially Suspicious Azure Front Door Connection
id: 8cb4d14e-776e-43c2-8fb9-91e7fcea32b4
status: test
description: |
    Detects connections with Azure Front Door (known legitimate service that can be leveraged for C2)
    that fall outside of known benign behavioral baseline (not using common apps or common azurefd.net endpoints)
references:
    - https://lots-project.com/site/2a2e617a75726566642e6e6574
    - https://medium.com/r3d-buck3t/red-teaming-in-cloud-leverage-azure-frontdoor-cdn-for-c2-redirectors-79dd9ca98178
    - https://www.fortalicesolutions.com/posts/hiding-behind-the-front-door-with-azure-domain-fronting
author: Isaac Dunham
date: 2024-11-07
tags:
    - attack.command-and-control
    - attack.t1102.002
    - attack.t1090.004
    - detection.threat-hunting
logsource:
    category: network_connection
    product: windows
detection:
    selection:
        DestinationHostname|contains: 'azurefd.net'
    filter_main_web_browsers:
        Image|endswith:
            - 'brave.exe'
            - 'chrome.exe'
            - 'chromium.exe'
            - 'firefox.exe'
            - 'msedge.exe'
            - 'msedgewebview2.exe'
            - 'opera.exe'
            - 'vivaldi.exe'
    filter_main_common_talkers:
        Image|endswith: 'searchapp.exe' # Windows search service uses signifcant amount of Azure FD
    filter_main_known_benign_domains:
        DestinationHostname|contains:
            - 'afdxtest.z01.azurefd.net' # used by Cortana; Cisco Umbrella top 1m
            - 'fp-afd.azurefd.net' # used by Cortana; Cisco Umbrella top 1m
            - 'fp-afdx-bpdee4gtg6frejfd.z01.azurefd.net' # used by Cortana; Cisco Umbrella top 1m
            - 'roxy.azurefd.net' # used by Cortana; Cisco Umbrella top 1m
            - 'powershellinfraartifacts-gkhedzdeaghdezhr.z01.azurefd.net' # Used by VS Code; Cisco Umbrella top 1m
            - 'storage-explorer-publishing-feapcgfgbzc2cjek.b01.azurefd.net' # Used by Azure Storage Explorer; Cisco Umbrella top 1m
            - 'graph.azurefd.net' # MS Graph; Cisco Umbrella top 1m
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Results are not inherently suspicious, but should be investigated during threat hunting for potential cloud C2.
    - Organization-specific Azure Front Door endpoints
level: medium