__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
___ __ __ _ ___
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\___ __|__ / \ \___
__________________________________________________________
INFORMATION BULLETIN
FreeBSD Security Vulnerabilities
(ppp, rdist, and rz)
July 18, 1996 16:00 GMT Number G-31
______________________________________________________________________________
PROBLEM: Three vulnerabilities have been found in the FreeBSD operating
system: 1) ppp program, 2) rdist, and 3) a "trojan horse" via rz
program.
PLATFORM: Vulnerabilities 1 and 2: All platforms running FreeBSD 2.0,
2.0.5, 2.1, 2.1-stable, and 2.2-current.
Vulnerability 3: All FreeBSD ports collections released before
2.1.5-RELEASE.
DAMAGE: 1) The ppp program does not properly manage user privileges,
allowing users to run any program with root access.
2) rdist creates an error message based on a user provided
string, without checking bounds on the buffer used. This buffer
is on the stack, and can therefore be used to execute arbitrary
instructions.
3) The rz program allows the sender of a file to request the
execution of arbitrary commands on the receiver's side. The
user using rz does not have any control over this feature.
SOLUTION: Install the proper patches and/or use the workarounds provided
below.
______________________________________________________________________________
VULNERABILITY Vulnerabilities 1 and 2 are widely known.
ASSESSMENT: Vulnerability 3 is relatively new.
______________________________________________________________________________
[Begin FreeBSD Bulletins]
1. ppp Program Vulnerability
===============================================================================
FreeBSD-SA-96:15 Security Advisory
FreeBSD, Inc.
Topic: security compromise from ppp
Category: core
Module: ppp
Announced: 1996-07-04
Affects: FreeBSD 2.0.5, 2.1, 2.1-stable, and 2.2-current
Corrected: 2.1-stable and 2.2-current as of 1996-06-10
FreeBSD only: unknown
Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:15/
=============================================================================
I. Background
FreeBSD ships a userland ppp program that can be used by users
to set up ppp connections.
This program is also known as ijppp.
The ppp program has a vulnerability that allows any user to run
commands under root privileges.
II. Problem Description
The ppp program does not properly manage user privileges, allowing
users to run any program with root privileges.
III. Impact
This vulnerability can only be exploited by users with a valid
account on the local system to easily obtain superuser access.
IV. Workaround
One may simply disable the setuid bit on all copies of the ppp
program. This will close the vulnerability but will only allow
the superuser to set up ppp connections.
As root, execute the commands:
# chmod 555 /usr/sbin/ppp
then verify that the setuid permissions of the files have been
removed. The permissions array should read "-r-xr-xr-x" as
shown here:
# ls -l /usr/sbin/ppp
-r-xr-xr-x 1 root bin 86016 Nov 16 1995 /usr/sbin/ppp
V. Solution
Patches are available which eliminate this vulnerability.
The following patch should be applied to the system sources and
ppp should be rebuilt and reinstalled. The first patch is against
the FreeBSD 2.1 and FreeBSD-stable source tree. The second patch
is for FreeBSD-current (version before 1996-06-10).
Apply the patch, then (being superuser):
# cd /usr/src/usr.sbin/ppp
# make depend
# make all
# make install
Index: command.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/command.c,v
retrieving revision 1.5.4.3
retrieving revision 1.5.4.4
diff -u -r1.5.4.3 -r1.5.4.4
--- command.c 1996/02/05 17:02:52 1.5.4.3
+++ command.c 1996/06/10 09:41:49 1.5.4.4
@@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
- * $Id: command.c,v 1.5.4.3 1996/02/05 17:02:52 dfr Exp $
+ * $Id: command.c,v 1.5.4.4 1996/06/10 09:41:49 ache Exp $
*
*/
#include <sys/types.h>
@@ -187,9 +187,14 @@
* We are running setuid, we should change to
* real user for avoiding security problems.
*/
- setgid( getgid() );
- setuid( getuid() );
-
+ if (setgid(getgid()) < 0) {
+ perror("setgid");
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ perror("setuid");
+ exit(1);
+ }
TtyOldMode();
if(argc > 0)
execvp(argv[0], argv);
Index: chat.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/chat.c,v
retrieving revision 1.4.4.1
retrieving revision 1.4.4.2
diff -u -r1.4.4.1 -r1.4.4.2
--- chat.c 1995/10/06 11:24:31 1.4.4.1
+++ chat.c 1996/06/10 09:41:45 1.4.4.2
@@ -18,7 +18,7 @@
* Columbus, OH 43221
* (614)451-1883
*
- * $Id: chat.c,v 1.4.4.1 1995/10/06 11:24:31 davidg Exp $
+ * $Id: chat.c,v 1.4.4.2 1996/06/10 09:41:45 ache Exp $
*
* TODO:
* o Support more UUCP compatible control sequences.
@@ -331,6 +331,15 @@
nb = open("/dev/tty", O_RDWR);
dup2(nb, 0);
LogPrintf(LOG_CHAT, "exec: %s\n", command);
+ /* switch back to original privileges */
+ if (setgid(getgid()) < 0) {
+ LogPrintf(LOG_CHAT, "setgid: %s\n", strerror(errno));
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ LogPrintf(LOG_CHAT, "setuid: %s\n", strerror(errno));
+ exit(1);
+ }
pid = execvp(command, vector);
LogPrintf(LOG_CHAT, "execvp failed for (%d/%d): %s\n", pid, errno, command);
exit(127);
Patch for FreeBSd-current before 1996-06-10:
Index: command.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/command.c,v
retrieving revision 1.17
retrieving revision 1.18
diff -u -r1.17 -r1.18
--- command.c 1996/05/11 20:48:22 1.17
+++ command.c 1996/06/09 20:40:58 1.18
@@ -17,7 +17,7 @@
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
- * $Id: command.c,v 1.17 1996/05/11 20:48:22 phk Exp $
+ * $Id: command.c,v 1.18 1996/06/09 20:40:58 ache Exp $
*
*/
#include <sys/types.h>
@@ -190,9 +190,14 @@
* We are running setuid, we should change to
* real user for avoiding security problems.
*/
- setgid( getgid() );
- setuid( getuid() );
-
+ if (setgid(getgid()) < 0) {
+ perror("setgid");
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ perror("setuid");
+ exit(1);
+ }
TtyOldMode();
if(argc > 0)
execvp(argv[0], argv);
Index: chat.c
===================================================================
RCS file: /home/ncvs/src/usr.sbin/ppp/chat.c,v
retrieving revision 1.10
retrieving revision 1.11
diff -u -r1.10 -r1.11
--- chat.c 1996/05/11 20:48:20 1.10
+++ chat.c 1996/06/09 20:40:56 1.11
@@ -18,7 +18,7 @@
* Columbus, OH 43221
* (614)451-1883
*
- * $Id: chat.c,v 1.10 1996/05/11 20:48:20 phk Exp $
+ * $Id: chat.c,v 1.11 1996/06/09 20:40:56 ache Exp $
*
* TODO:
* o Support more UUCP compatible control sequences.
@@ -393,6 +393,15 @@
nb = open("/dev/tty", O_RDWR);
dup2(nb, 0);
LogPrintf(LOG_CHAT_BIT, "exec: %s\n", command);
+ /* switch back to original privileges */
+ if (setgid(getgid()) < 0) {
+ LogPrintf(LOG_CHAT_BIT, "setgid: %s\n", strerror(errno));
+ exit(1);
+ }
+ if (setuid(getuid()) < 0) {
+ LogPrintf(LOG_CHAT_BIT, "setuid: %s\n", strerror(errno));
+ exit(1);
+ }
pid = execvp(command, vector);
LogPrintf(LOG_CHAT_BIT, "execvp failed for (%d/%d): %s\n", pid, errno, command);
exit(127);
=============================================================================
2. rdist Vulnerability
=============================================================================
FreeBSD-SA-96:16 Security Advisory
Revised: Fri Jul 12 09:32:53 PDT 1996 FreeBSD, Inc.
Topic: security vulnerability in rdist
Category: core
Module: rdist
Announced: 1996-07-12
Affects: FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current
Corrected: 2.1-stable and 2.2-current as of 1996-07-11
Source: 4.4BSD (lite)
FreeBSD only: no
Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:16/
Reference: [8lgm]-Advisory-26.UNIX.rdist.20-3-1996
=============================================================================
I. Background
A bug was found in the BSD rdist utility which can allow
an unprivileged local user to gain unauthorized access.
This problem is present in all source code and binary
distributions of FreeBSD version 2.x released before 1996-07-12.
rdist has been the subject of security vulnerabilities in the past.
This is a newly discovered vulnerability not related to previous
race conditions fixed in rdist.
II. Problem Description
rdist creates an error message based on a user provided string,
without checking bounds on the buffer used. This buffer is
on the stack, and can therefore be used to execute arbitrary
instructions.
III. Impact
This vulnerability can allow a local user to obtain superuser
privileges. It may only be exploited by users with a valid
account on the local system. It is present in almost all BSD
derived operating systems with a "setuid" rdist program.
IV. Workaround
The rdist program must be setuid root to function properly.
This vulnerability can be eliminated by making rdist not
executable by unprivileged users. Since this limits the
usefulness of the program, a software update is advised.
This workaround will work for all versions of FreeBSD affected
by this problem.
As root, execute the commands:
# chflags noschg /usr/bin/rdist
# chmod u-s,go-rx /usr/bin/rdist
then verify that the setuid permissions of the files have been
removed. The permissions array should read "-r-x------" as
shown here:
# ls -l /usr/bin/rdist
-r-x------ 1 root bin 49152 Jun 16 10:46 rdist
V. Solution(s)
Apply the available via FTP from the patch directory noted
at the top of this message. Recompile, and reinstall the
rdist program. This patch is known to apply to all
FreeBSD 2.x systems, it has not been tested with FreeBSD 1.x.
The [8lgm] organization correctly points out that this program
does not have a particularly good security "history." While
the patch for this vulnerability does solve this particular
problem, it's not clear if other security issues involving rdist
will appear in the future.
Administrators should consider whether it is appropriate to
remove the standard rdist program and upgrade to rdist
version 6, which is available as a FreeBSD port.
FreeBSD, Inc. has not replaced the standard BSD rdist with
the newer code because the new rdist is not protocol-compatible
with the original version.
=============================================================================
3. rz Program Vulnerability
=============================================================================
FreeBSD-SA-96:17 Security Advisory
Revised: Tue Jul 16 21:44:54 PDT 1996 FreeBSD, Inc.
Topic: "Trojan Horse" vulnerability via rz program
Category: ports
Module: rzsz
Announced: 1996-07-16
Affects: All FreeBSD ports collections released before 2.1.5-RELEASE
Corrected: ports collection as of 1996-07-06
Source: rzsz shareware package
FreeBSD only: no
Patches: ftp://freebsd.org/pub/CERT/patches/SA-96:17/
=============================================================================
I. Background
All existing versions of the rz program (a program for receiving
files over serial lines using the Z-Modem protocol) are equipped
with a feature that allows the sender of a file to request the
execution of arbitrary commands on the receiver's side. The user
using rz does not have any control over this feature.
The workaround is to have rz never execute any command, and
always pretend a successful execution.
All FreeBSD users are encouraged to use the workaround provided.
Since the intent of the Z-Modem protocol is to provide a reliable
connection between systems of a vastly different architecture,
the execution of local commands at request of the sending side
cannot even be considered a useful feature at all.
II. Problem Description
The Z-Modem protocol specifies a mechanism which allows the
transmitter of a file to execute an arbitrary command string
as part of the file transfer. This is typically used to rename
files or eliminate temporary files. A malicious "trusted" sender
could send down a command that could damage a user's environment.
III. Impact
The rzsz package is an optional port that made be installed on
some FreeBSD systems. This program is not installed by default.
Systems without this program are not vulnerable.
rz allows "Trojan Horse" type attacks against unsuspecting users.
Since the rz executable does not run with special privileges,
the vulnerability is limited to changes in the operating environment
that the user could willingly perform.
This vulnerability is a fundamental flaw in the Z-Modem protocol.
Other operating systems and other implementations of the Z-Modem
protocol may also suffer similar vulnerabilities.
IV. Workaround
Disable the rz program. If it has been installed, it would
typically be found in /usr/local/bin.
# chmod 000 /usr/local/bin/rz
# ls -l /usr/local/bin/rz
---------- 1 root wheel 23203 Mar 4 23:12 /usr/local/bin/rz
V. Solution(s)
This feature is a relatively unknown part of the Z-Modem protocol.
It is not critical to file transfers in general. The safest
approach is to disable this feature in the receiving program.
Any rzsz port that is obtained from the official ports collection
after 1996-07-06 includes the following patch to disable this feature.
This patch applies to rzsz v3.42, if you have an earlier version
of the rzsz sources, please upgrade to the latest version first.
*** rz.c.orig Sat Jul 6 17:34:26 1996
--- rz.c Sat Jul 6 17:44:52 1996
***************
*** 1020,1039 ****
--- 1020,1045 ----
case ZCOMMAND:
cmdzack1flg = Rxhdr[ZF0];
if (zrdata(secbuf, 1024) == GOTCRCW) {
+ #ifdef BIG_SECURITY_HOLE
void exec2();
if (cmdzack1flg & ZCACK1)
stohdr(0L);
else
stohdr((long)sys2(secbuf));
+ #else
+ stohdr(0L);
+ #endif
purgeline(); /* dump impatient questions */
do {
zshhdr(4,ZCOMPL, Txhdr);
}
while (++errors<20 && zgethdr(Rxhdr) != ZFIN);
ackbibi();
+ #ifdef BIG_SECURITY_HOLE
if (cmdzack1flg & ZCACK1)
exec2(secbuf);
+ #endif
return ZCOMPL;
}
zshhdr(4,ZNAK, Txhdr); goto again;
=============================================================================
FreeBSD, Inc.
Web Site: http://www.freebsd.org/
Confidential contacts: security-officer@freebsd.org
PGP Key: ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications: security-notifications@freebsd.org
Security public discussion: security@freebsd.org
Notice: Any patches in this document may not apply cleanly due to
modifications caused by digital signature or mailer software.
Please reference the URL listed at the top of this document
for original copies of all patches if necessary.
=============================================================================
[End FreeBSD Bulletins]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of FreeBSD, Inc. for the
information contained in this bulletin.
_______________________________________________________________________________
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