Suspicious File Write to SharePoint Layouts Directory — Sigma Rule

Rule metadata and linked tags

Author: Swachchhanda Shrawan Poudel (Nextron Systems). Source status: experimental; severity: high. Source dates: 2025-07-24 / not supplied.

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

Pinned original Sigma rule · Detection Rule License 1.1

Source SHA-256: 972534517212498d5e6a30011d4783d4bc823b556d82b5f6969d393b8b5988d6

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 File Write to SharePoint Layouts Directory
id: 1f0489be-b496-4ddf-b3a9-5900f2044e9c
status: experimental
description: |
    Detects suspicious file writes to SharePoint layouts directory which could indicate webshell activity or post-exploitation.
    This behavior has been observed in the exploitation of SharePoint vulnerabilities such as CVE-2025-49704, CVE-2025-49706 or CVE-2025-53770.
references:
    - https://unit42.paloaltonetworks.com/microsoft-sharepoint-cve-2025-49704-cve-2025-49706-cve-2025-53770/
    - https://www.microsoft.com/en-us/security/blog/2025/07/22/disrupting-active-exploitation-of-on-premises-sharepoint-vulnerabilities/
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-07-24
tags:
    - attack.initial-access
    - attack.t1190
    - attack.persistence
    - attack.t1505.003
logsource:
    product: windows
    category: file_event
detection:
    selection:
        Image|endswith:
            - '\cmd.exe'
            - '\powershell_ise.exe'
            - '\powershell.exe'
            - '\pwsh.exe'
            - '\w3wp.exe'
        TargetFilename|startswith:
            - 'C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\'
            - 'C:\Program Files (x86)\Common Files\Microsoft Shared\Web Server Extensions\'
        TargetFilename|contains:
            - '\15\TEMPLATE\LAYOUTS\'
            - '\16\TEMPLATE\LAYOUTS\'
        TargetFilename|endswith:
            - '.asax'
            - '.ascx'
            - '.ashx'
            - '.asmx'
            - '.asp'
            - '.aspx'
            - '.bat'
            - '.cmd'
            - '.cer'
            - '.config'
            - '.hta'
            - '.js'
            - '.jsp'
            - '.jspx'
            - '.php'
            - '.ps1'
            - '.vbs'
    condition: selection
falsepositives:
    - Unknown
level: high

Original YAML and metadata in JSON

False positives

• Unknown

Source references

• https://unit42.paloaltonetworks.com/microsoft-sharepoint-cve-2025-49704-cve-2025-49706-cve-2025-53770/
• https://www.microsoft.com/en-us/security/blog/2025/07/22/disrupting-active-exploitation-of-on-premises-sharepoint-vulnerabilities/