Webshell ReGeorg Detection Via Web Logs — Sigma Rule

Rule metadata and linked tags

Author: Cian Heasley. Source status: test; severity: high. Source dates: 2020-08-04 / 2023-01-02.

{
  "category": "webserver"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: b76510bdb9979e1336957b3504aa9bf0bdb888989c601510daa7e65ced9642e2

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: Webshell ReGeorg Detection Via Web Logs
id: 2ea44a60-cfda-11ea-87d0-0242ac130003
status: test
description: Certain strings in the uri_query field when combined with null referer and null user agent can indicate activity associated with the webshell ReGeorg.
references:
    - https://community.rsa.com/community/products/netwitness/blog/2019/02/19/web-shells-and-netwitness-part-3
    - https://github.com/sensepost/reGeorg
author: Cian Heasley
date: 2020-08-04
modified: 2023-01-02
tags:
    - attack.persistence
    - attack.t1505.003
logsource:
    category: webserver
detection:
    selection:
        cs-uri-query|contains:
            - 'cmd=read'
            - 'connect&target'
            - 'cmd=connect'
            - 'cmd=disconnect'
            - 'cmd=forward'
    filter:
        cs-referer: null
        cs-user-agent: null
        cs-method: POST
    condition: selection and filter
falsepositives:
    - Web applications that use the same URL parameters as ReGeorg
level: high

Original YAML and metadata in JSON

False positives

• Web applications that use the same URL parameters as ReGeorg

Source references

• https://community.rsa.com/community/products/netwitness/blog/2019/02/19/web-shells-and-netwitness-part-3
• https://github.com/sensepost/reGeorg