title: Antivirus Web Shell Detection
id: fdf135a2-9241-4f96-a114-bb404948f736
description: Detects a highly relevant Antivirus alert that reports a web shell. It's highly recommended to tune this rule to the specific strings used by your anti virus solution by downloading a big webshell repo from e.g. github and checking the matches.
date: 2018/09/09
modified: 2021/05/08
author: Florian Roth, Arnim Rupp
references:
    - https://www.nextron-systems.com/2021/03/25/antivirus-event-analysis-cheat-sheet-v1-8/
    - https://github.com/tennc/webshell
    - https://www.virustotal.com/gui/file/bd1d52289203866645e556e2766a21d2275877fbafa056a76fe0cf884b7f8819/detection
    - https://www.virustotal.com/gui/file/308487ed28a3d9abc1fec7ebc812d4b5c07ab025037535421f64c60d3887a3e8/detection
    - https://www.virustotal.com/gui/file/7d3cb8a8ff28f82b07f382789247329ad2d7782a72dde9867941f13266310c80/detection
    - https://www.virustotal.com/gui/file/e841675a4b82250c75273ebf0861245f80c6a1c3d5803c2d995d9d3b18d5c4b5/detection
    - https://www.virustotal.com/gui/file/a80042c61a0372eaa0c2c1e831adf0d13ef09feaf71d1d20b216156269045801/detection
    - https://www.virustotal.com/gui/file/b219f7d3c26f8bad7e175934cd5eda4ddb5e3983503e94ff07d39c0666821b7e/detection
    - https://www.virustotal.com/gui/file/b8702acf32fd651af9f809ed42d15135f842788cd98d81a8e1b154ee2a2b76a2/detection
tags:
    - attack.persistence
    - attack.t1100
    - attack.t1505.003
logsource:
    product: antivirus
detection:
    selection:
        - Signature|startswith:
            - "PHP/"
            - "JSP/"
            - "ASP/"
            - "Perl/"
            - "PHP."
            - "JSP."
            - "ASP."
            - "Perl."
            - "VBS/Uxor" # looking for "VBS/" would also find downloaders and droppers meant for desktops
            - "IIS/BackDoor"
            - "JAVA/Backdoor"
            - "Troj/ASP"
            - "Troj/PHP"
            - "Troj/JSP"
        - Signature|contains:
            - "Webshell"
            - "Chopper"
            - "SinoChoper"
            - "ASPXSpy"
            - "Aspdoor"
            - "filebrowser"
            - "PHP_"
            - "JSP_"
            - "ASP_" # looking for "VBS_" would also find downloaders and droppers meant for desktops
            - "PHP:"
            - "JSP:"
            - "ASP:"
            - "Perl:"
            - "PHPShell"
            - "Trojan.PHP"
            - "Trojan.ASP"
            - "Trojan.JSP"
            - "Trojan.VBS"
            - "PHP?Agent"
            - "ASP?Agent"
            - "JSP?Agent"
            - "VBS?Agent"
            - "Backdoor?PHP"
            - "Backdoor?JSP"
            - "Backdoor?ASP"
            - "Backdoor?VBS"
            - "Backdoor?Java"
    condition: selection
fields:
    - FileName
    - User
falsepositives:
    - Unlikely
level: critical