Suspicious WebDav Client Execution Via Rundll32.EXE — Sigma Rule

Rule metadata and linked tags

Author: Nasreddine Bencherchali (Nextron Systems), Florian Roth (Nextron Systems). Source status: test; severity: high. Source dates: 2023-03-16 / 2023-09-18.

{
  "category": "process_creation",
  "product": "windows"
}

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: ec0f71854a8f1de9ac18e1fb7b13db9d7c406f29d4e65034f7b7195922fb9ec7

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: Suspicious WebDav Client Execution Via Rundll32.EXE
id: 982e9f2d-1a85-4d5b-aea4-31f5e97c6555
status: test
description: |
    Detects "svchost.exe" spawning "rundll32.exe" with command arguments like C:\windows\system32\davclnt.dll,DavSetCookie. This could be an indicator of exfiltration or use of WebDav to launch code (hosted on WebDav Server) or potentially a sign of exploitation of CVE-2023-23397
references:
    - https://twitter.com/aceresponder/status/1636116096506818562
    - https://www.mdsec.co.uk/2023/03/exploiting-cve-2023-23397-microsoft-outlook-elevation-of-privilege-vulnerability/
    - https://www.pwndefend.com/2023/03/15/the-long-game-persistent-hash-theft/
    - https://www.microsoft.com/en-us/security/blog/wp-content/uploads/2023/03/Figure-7-sample-webdav-process-create-event.png
    - https://www.microsoft.com/en-us/security/blog/2023/03/24/guidance-for-investigating-attacks-using-cve-2023-23397/
author: Nasreddine Bencherchali (Nextron Systems), Florian Roth (Nextron Systems)
date: 2023-03-16
modified: 2023-09-18
tags:
    - attack.exfiltration
    - attack.t1048.003
    - cve.2023-23397
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\svchost.exe'
        ParentCommandLine|contains: '-s WebClient'
        Image|endswith: '\rundll32.exe'
        CommandLine|contains: 'C:\windows\system32\davclnt.dll,DavSetCookie'
        CommandLine|re: '://\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}'
    filter_local_ips:
        CommandLine|contains:
            - '://10.' # 10.0.0.0/8
            - '://192.168.' # 192.168.0.0/16
            - '://172.16.' # 172.16.0.0/12
            - '://172.17.'
            - '://172.18.'
            - '://172.19.'
            - '://172.20.'
            - '://172.21.'
            - '://172.22.'
            - '://172.23.'
            - '://172.24.'
            - '://172.25.'
            - '://172.26.'
            - '://172.27.'
            - '://172.28.'
            - '://172.29.'
            - '://172.30.'
            - '://172.31.'
            - '://127.' # 127.0.0.0/8
            - '://169.254.' # 169.254.0.0/16
    condition: selection and not 1 of filter_*
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://twitter.com/aceresponder/status/1636116096506818562
• https://www.mdsec.co.uk/2023/03/exploiting-cve-2023-23397-microsoft-outlook-elevation-of-privilege-vulnerability/
• https://www.pwndefend.com/2023/03/15/the-long-game-persistent-hash-theft/
• https://www.microsoft.com/en-us/security/blog/wp-content/uploads/2023/03/Figure-7-sample-webdav-process-create-event.png
• https://www.microsoft.com/en-us/security/blog/2023/03/24/guidance-for-investigating-attacks-using-cve-2023-23397/