Hi fellow users! The members of GOBBLES Research have discovered a flaw in the authentication protocol for Yahoo! Messenger. Attached to this letter is a full disclosure advisory + discussion of the vulnerability. At this time there is no "fix" available. Thanks for all your support! The GOBBLES Research Team http://www.bugtraq.org ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++GOBBLES+SECURITY+RESEARCH+TEAM+INCORPORATED+++++++++++++++++ ALERT! ALERT! YAHOO MESSENGER REPLAY ATTACK! ALERT! ALERT! ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ "Overt control... always has a finite life, because in the end there will be a challenge and rebellion against it. Covert control... can go on forever, because you don't rebel against something you don't know exists." oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo PRODUCT ******* program: Yahoo! Messenger YMSG protocol website: http://messenger.yahoo.com/ BACKGROUND ********** GOBBLES was sitting down in lab with Yahoo! Messenger client running chatting with beautiful Susie who on he friends list on Yahoo. GOBBLES trying finish read Bruce Schneier _Applied Cryptography_ but Susie keep buzzing like crazy about music and pets (she say she has nice pussy) and then suddenly she say she writing some SPARC assembly codes and GOBBLES just go crazy hehe. Anyway after GOBBLES wake up to see she still talk about silly gossip, he click 'ignore' button and begin determined to break Messenger protocol with he new crypto knowledge. GOBBLES discovered very inane move made by Yahoo engineers in apparent effort to stop cleartext transmission of password during initial login packet exchange. Without full disclosure this hole not brought to public attention and make Yahoo more secure, so how can idiot say that full disclosure only secure a job? It wrong saying that only people who defend full disclosure are they who capitalize on it because not like GOBBLES acquire sports car working at GOBBLES BUGTRAQ SECURITY INC. When aleph1 leave r00t hacking group to be security professional he not profit like everyone say, so why everyone have to give these people hard time if they become security professional and contribute earth-shattering vulnerability like GOBBLES does in order to improve security and liberate humanity from darkside malicious cracker out there in wild? Revealing symlink vulnerability in Bruce Piano Tuner v0.7 help admin protect system from cracker out there and make cracker lose root. GOBBLES owes securityfocus website great deal because they provide helpful information that help me with cracking incident last year. This cracker he come on one of my system using team bugtraq penetrator exploit in bad way because GOBBLES was asleep and couldn't apply patch before cracker gank it from bugtraq. Anyway, cracker not do any damage, but he thought it his base. With patch information from securityfocus, GOBBLES was able fix security hole and lock him out :P TECHNICAL DETAILS ***************** GOBBLES look at Dug Song dsniff msgsnarf.c and observe that YMSG application header have following format: struct ymsg { unsigned char version[8]; unsigned short length; unsigned short type; unsigned char unknown1[4]; unsigned char unknown2[4]; } GOBBLES look at libyahoo code from sourceforge and observe: /* Service constants */ #define YAHOO_SERVICE_LOGON 1 GOBBLES doing this on FreeBSD machine so he get patch for like... FreeBSD-SA-01:48 Security Advisory FreeBSD, Inc. Topic: tcpdump contains remote buffer overflow Category: core Module: tcpdump Announced: 2001-07-17 Credits: Nick Cleaton <nickat_private> Affects: All releases of FreeBSD 4.x prior to 4.4, FreeBSD 4.3-STABLE prior to the correction date FreeBSD 3.x is unaffected. Corrected: 2001-07-09 Vendor status: Patch released FreeBSD only: NO ... this so while he run tcpdump next he won't be compromised by darkside malicious cracker out there in wild or penetrator typing in wrong host to Vetescan stealth vulnerability assessment tool. GOBBLES then run tcpdump and using YMSG structure above as reference he find first packet with service type constant 0x01. This LOGIN packet. GOBBLES notice it use MCF/MD5 encryption of user password with crypt(3) salt like $1$_2S43d5f$. Encrypted password is sent over the wire in LOGIN packet. User is immediately authenticated. MAJOR VULNERABILITY #1 IS THAT ATTACKER MAY SNIFF THIS AND BRUTE FORCE USER PASSWORD AKIN TO RECENT TEAM BUGTRAQ POP3 'APOP PASSWORDS AT RISK' ADVISORY: http://archives.neohapsis.com/archives/bugtraq/2001-07/0163.html MAJOR VULNERABILITY #2 IS THAT ATTACKER WHO CAPTURES LOGIN PACKET CAN USE SIMPLE REPLAY ATTACK WITH PASSWORD HASH INJECTED IN PACKET SENT BY CUSTOM CLIENT. So only defense afforded by this dumb scheme over sending password unencrypted is protection against password reuse attack: "Sociological Ghasche Tree Model And Its Ramifications Concerning Password Reuse On Worldwide Computer Networks - USENIX 1999" http://www.sec-lab.cs.qwe.edu/professors/Floyd/whitepapers/1999/reuse.pdf FIX *** GOBBLES suggest Yahoo engineer use brain and come up with challenge-response mechanism. They set bad example for commercial security research community. They should pull finger out of bum and focus on protecting user instead of just pulling in money from job. Here $0.2 -- go buy clue. DEMONSTRATION ************* As you see above, easy to observe packets with tcpdump. Ethereal not seem to have YMSG protocol support yet, so SANS professional at sans.org might need make $50,000/hour other way by using different tool for analysis instead of ethereal. Come with most operating system is tcpdump or snoop. Can also get sweet tool ngrep from route[GUARDENT] site: http://www.packetfactory.net/ Or maybe you be creative and roll your own with Michael Schiffman libnet socket wrapper. It easy reproduce, no hurry, just take your time and see what you come up with. GREETS ****** dianora / evil angelica, tsk, snow, carolyn meinel, john vranesevich, steve gibson, kimble, knightmare, emmanuel goldstein, box.sk, @stake, securityfocus, sans.org, blackhat.com, defcon.org, 2600.com, #phrack@efnet, #hackphreak@undernet, bugtraq (thanks aleph1 and david ahmad for devoting your time to a great list), ntbugtraq (russel the love muscle ;D), cert.org, paul vixie, vesselin bontchev, reese witherspoon, kirsten dunst, katie holmes, aleister crowley, manly p hall, franz bardon, dennis ritchie, nietzsche, w. richard stevens, radiohead, george michael, larry wall, beethoven, francis bacon, bruce willis, bruce schneier, alan turing, john von neumann, donald knuth, michael abrash, robert sedgewick, and all our friends and family. GOBBLES SECURITY http://www.bugtraq.org/
This archive was generated by hypermail 2b30 : Wed Nov 21 2001 - 19:41:50 PST