__________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN OpenSSH Buffer Management Error September 17, 2003 17:00 GMT Number N-151 [REVISED 22 Sept 2003] [REVISED 23 Sept 2003] [REVISED 1 Oct 2003] [REVISED 2 Oct 2003] [REVISED 27 Oct 2003] [REVISED 16 Dec 2003] [REVISED 18 Apr 2005] ______________________________________________________________________________ PROBLEM: OpenSSH has announced an upgrade that fixes a buffer management error. When a function that expands the size of a buffer detects that the new size will be greater then 10Meg it generates a fatal error. When the error is generated, the function incorrectly sets the size of the allocated buffer to a value larger than the actual allocation. The fatal error processing routines will then attempt to deallocate more memory than was allocated. PLATFORM: -All systems using versions of OpenSSH earlier than 3.7 -Hewlett Packard HP-UX B.11.00, B.11.11, B.11.22 only with the T1471AA HP-UX Secure Sheel product installed. -Hewlett Packard HP-UX B.11.23 -Mac OS X versions prior to 10.2.8 -IRIX 6.5.22 -SPARC Solaris 9 -x86 Solaris 9 -Red Hat Linux products -Sun Linux 5.0 with OpenSSH versions 3.1p1-6 or earlier -Sun Cobalt RaQ550 with OpenSSH-3.5p1-1C1stackguard or earlier DAMAGE: Could possibly cause a system to crash. SOLUTION: Upgrade to OpenSSH version 3.7.1. Download and install appropriate files from appropriate vendor. ______________________________________________________________________________ VULNERABILITY The risk is LOW. There are no known exploits. We believe it is ASSESSMENT: unlikely that this problem can be exploited. If it can be exploited, it might be possible to crash a system that does not use protected memory (Windows 95, 98, ME). On systems with protected memory (UNIX, Linux, Windows NT, 2000, XP) you might be able to crash ssh but it is already shutting down because of the fatal error. ______________________________________________________________________________ LINKS: CIAC BULLETIN: http://www.ciac.org/ciac/bulletins/n-151.shtml ORIGINAL BULLETIN: http://www.openssh.com/txt/buffer.adv ADDITIONAL LINKS: http://www.cert.org/advisories/CA-2003-24.html RED HAT https://rhn.redhat.com/errata/RHSA-2003-279.html https://rhn.redhat.com/errata/RHSA-2003-280.html CISCO http://www.cisco.com/warp/public/707/cisco-sa-20030917- openssh.shtml Visit HEWLETT PACKARD Subscription Service for: HPSBUX0309-282 (SSRT3629)(rev.1) Apple Security Advisory - Mac OS X 10.2.8 (APPLE-SA-2003-09-22) http://net-security.org/advisory.php?id=2546 http://docs.info.apple.com/article.html?artnum=61798 SGI Security Advisory 20030904-01-P http://www.sgi.com/support/security/advisories.html Sun Alert ID: 56861 http://www.sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsalert% 2F56861&zone_32=category%3Asecurity Sun Alert ID: 56862 http://www.sunsolve.sun.com/search/document.do?assetkey=1 -26-56862-1&searchclause=%22category:security%22%20%22 availability,%20security%22 ______________________________________________________________________________ REVISION HISTORY: 9/22/03 - Updated PLATFORM section; SOLUTION section; and added link for Hewlett Packard HPSBUX0309-282 (SSRT3629). 9/23/03 - Updated PLATFORM section; SOLUTION section; and added link for Apple Security Advisory - Mac OS X 10.2.8 (APPLE-SA-2003-09-22). 10/1/03 - Updated PLATFORM section; added link for SGI Security Advisory 20030904-01-P. 10/2/03 - Added link for Sun Alert ID: 56861 and updated PLATFORM section. 10/27/03 - Added link for Red Hat Advisory RHSA-2003:280 for information on patches to their Red Hat Enterprise Linux products. 12/16/03 - Added Hewlett Packard HP-UX B.11.23 as an affected platform with patches now available. HPSBUX0309-282 (rev. 1) 04/18/05 - revised to add a link to Sun Alert ID: 56862 for Sun Linux 5.0 with OpenSSH versions 3.1p1-6 or earlier and Sun Cobalt RaQ550 with OpenSSH-3.5p1-1C1stackguard or earlier. The description of this vulnerability exposes the fact that if a buffer in sshd can be expanded beyond about 10Meg, that sshd will shut down by design. It may be possible to exploit this feature but only to the copy of sshd that you are connected to. That is, you can possibly kill your own process. [****** Start OpenSSH Bulletin ******] Subject: OpenSSH Security Advisory: buffer.adv This is the 2nd revision of the Advisory. This document can be found at: http://www.openssh.com/txt/buffer.adv 1. Versions affected: All versions of OpenSSH's sshd prior to 3.7.1 contain buffer management errors. It is uncertain whether these errors are potentially exploitable, however, we prefer to see bugs fixed proactively. Other implementations sharing common origin may also have these issues. 2. Solution: Upgrade to OpenSSH 3.7.1 or apply the following patch. =================================================================== Appendix A: patch for OpenSSH 3.6.1 and earlier Index: buffer.c =================================================================== RCS file: /cvs/src/usr.bin/ssh/buffer.c,v retrieving revision 1.16 retrieving revision 1.18 diff -u -r1.16 -r1.18 --- buffer.c 26 Jun 2002 08:54:18 -0000 1.16 +++ buffer.c 16 Sep 2003 21:02:39 -0000 1.18 @@ -23,8 +23,11 @@ void buffer_init(Buffer *buffer) { - buffer->alloc = 4096; - buffer->buf = xmalloc(buffer->alloc); + const u_int len = 4096; + + buffer->alloc = 0; + buffer->buf = xmalloc(len); + buffer->alloc = len; buffer->offset = 0; buffer->end = 0; } @@ -34,8 +37,10 @@ void buffer_free(Buffer *buffer) { - memset(buffer->buf, 0, buffer->alloc); - xfree(buffer->buf); + if (buffer->alloc > 0) { + memset(buffer->buf, 0, buffer->alloc); + xfree(buffer->buf); + } } /* @@ -69,6 +74,7 @@ void * buffer_append_space(Buffer *buffer, u_int len) { + u_int newlen; void *p; if (len > 0x100000) @@ -98,11 +104,13 @@ goto restart; } /* Increase the size of the buffer and retry. */ - buffer->alloc += len + 32768; - if (buffer->alloc > 0xa00000) + + newlen = buffer->alloc + len + 32768; + if (newlen > 0xa00000) fatal("buffer_append_space: alloc %u not supported", - buffer->alloc); - buffer->buf = xrealloc(buffer->buf, buffer->alloc); + newlen); + buffer->buf = xrealloc(buffer->buf, newlen); + buffer->alloc = newlen; goto restart; /* NOTREACHED */ } Index: channels.c =================================================================== RCS file: /cvs/src/usr.bin/ssh/channels.c,v retrieving revision 1.194 retrieving revision 1.195 diff -u -r1.194 -r1.195 --- channels.c 29 Aug 2003 10:04:36 -0000 1.194 +++ channels.c 16 Sep 2003 21:02:40 -0000 1.195 @@ -228,12 +228,13 @@ if (found == -1) { /* There are no free slots. Take last+1 slot and expand the array. */ found = channels_alloc; - channels_alloc += 10; if (channels_alloc > 10000) fatal("channel_new: internal error: channels_alloc %d " "too big.", channels_alloc); + channels = xrealloc(channels, + (channels_alloc + 10) * sizeof(Channel *)); + channels_alloc += 10; debug2("channel: expanding %d", channels_alloc); - channels = xrealloc(channels, channels_alloc * sizeof (Channel *)); for (i = found; i < channels_alloc; i++) channels[i] = NULL; } =================================================================== Appendix B: patch for OpenSSH 3.7 Index: buffer.c =================================================================== RCS file: /cvs/src/usr.bin/ssh/buffer.c,v retrieving revision 1.17 retrieving revision 1.18 diff -u -r1.17 -r1.18 --- buffer.c 16 Sep 2003 03:03:47 -0000 1.17 +++ buffer.c 16 Sep 2003 21:02:39 -0000 1.18 @@ -23,8 +23,11 @@ void buffer_init(Buffer *buffer) { - buffer->alloc = 4096; - buffer->buf = xmalloc(buffer->alloc); + const u_int len = 4096; + + buffer->alloc = 0; + buffer->buf = xmalloc(len); + buffer->alloc = len; buffer->offset = 0; buffer->end = 0; } @@ -34,8 +37,10 @@ void buffer_free(Buffer *buffer) { - memset(buffer->buf, 0, buffer->alloc); - xfree(buffer->buf); + if (buffer->alloc > 0) { + memset(buffer->buf, 0, buffer->alloc); + xfree(buffer->buf); + } } /* Index: channels.c =================================================================== RCS file: /cvs/src/usr.bin/ssh/channels.c,v retrieving revision 1.194 retrieving revision 1.195 diff -u -r1.194 -r1.195 --- channels.c 29 Aug 2003 10:04:36 -0000 1.194 +++ channels.c 16 Sep 2003 21:02:40 -0000 1.195 @@ -228,12 +228,13 @@ if (found == -1) { /* There are no free slots. Take last+1 slot and expand the array. */ found = channels_alloc; - channels_alloc += 10; if (channels_alloc > 10000) fatal("channel_new: internal error: channels_alloc %d " "too big.", channels_alloc); + channels = xrealloc(channels, + (channels_alloc + 10) * sizeof(Channel *)); + channels_alloc += 10; debug2("channel: expanding %d", channels_alloc); - channels = xrealloc(channels, channels_alloc * sizeof (Channel *)); for (i = found; i < channels_alloc; i++) channels[i] = NULL; } =================================================================== [****** End OpenSSH Bulletin ******] _______________________________________________________________________________ CIAC wishes to acknowledge the contributions of OpenSSH for the information contained in this bulletin. _______________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). 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