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The U.S. Department of Energy
Computer Incident Advisory Capability
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/ | /_\ /
\___ __|__ / \ \___
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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]
______________________________________________________________________________
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.
Mac OS X versions prior to 10.2.8
IRIX 6.5.22
SPARC Solaris 9
x86 Solaris 9
Red Hat Linux products
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)
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
______________________________________________________________________________
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.
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). CIAC is located at the Lawrence Livermore
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