__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
___ __ __ _ ___
/ | /_\ /
\___ __|__ / \ \___
__________________________________________________________
INFORMATION BULLETIN
Vulnerabilities in PCNFSD Program
April 22, 1996 17:00 GMT Number G-21
______________________________________________________________________________
PROBLEM: Two vulnerabilities exist in the pcnfsd program.
PLATFORM: The pcnfsd program (also called rpc.pcnfsd) runs on a UNIX
server.
DAMAGE: The first vulnerability allows local users to change the
permissions on any file accessible to the local system that the
root user can change. The second vulnerability allows remote
users to execute arbitrary commands as root on the machine
where pcnfsd runs.
SOLUTION: Check for vulnerabilities and install the proper patch. If
patch is unavailable from vendor, consider using the public
available version describe below.
______________________________________________________________________________
VULNERABILITY Knowledge of how to exploit these vulnerabilities are widely
ASSESSMENT: known.
______________________________________________________________________________
CIAC has obtained information from CERT pertaining to the vulnerabilities
in the pcnfsd program. CIAC recommends that you install the proper patch
and/or follow the solutions described below.
[ Start of CERT Advisory ]
I. Description
The pcnfsd program (also called rpc.pcnfsd) is an authentication and
printing program that runs on a UNIX server. There are many publicly
available versions, and several vendors supply their own version.
pcnfsd supports a printing model that uses NFS to transfer files from
a client to the pcnfsd server. (Note: pcnfsd does *not* provide NFS
services.) When a client wants to print a file, it requests the path
to a spool directory from the server. The client then writes the necessary
files for printing using NFS, and informs the pcnfsd server that the
files are ready for printing.
pcnfsd creates a subdirectory for each of its clients using the client's
hostname, then returns this path name to the client. The returned path
name must be exported via to its clients by the NFS server. The
NFS server and the pcnfsd server may be two separate machines.
The first vulnerability is that pcnfsd, which runs as root, creates the
aforementioned directories with mkdir(2) and then changes their mode
with chmod(2) to mode 777. If the target directory is replaced with a
symbolic link pointing to a restricted file or directory, the mkdir(2)
will fail but the chmod(2) will succeed. This means that the target of
the symbolic link will be mode 777.
Note that pcnfsd must run as root when servicing print requests so that
it can assume the identity of the PC user when interacting with UNIX
print commands. On some systems, pcnfsd may also have to run as root so
it can read restricted files when carrying out authentication tasks.
The second vulnerability is that pcnfsd calls the system(3) subroutine
as root, and the string passed to system(3) can be influenced by the
arguments given in the remote procedure call. Remote users can execute
arbitrary commands on the machine where pcnfsd runs.
II. Impact
For the first vulnerability, local users can change the permissions on
any file accessible to the local system that the root user can change.
For the second vulnerability, remote users can execute arbitrary commands
as root on the machine where pcnfsd runs.
III. Solution
If you are using pcnfsd from a vendor, consult the vendor list in
Section A. If your vendor is not listed, we recommend that you
contact your vendor directly.
Until a vendor patch is available, we recommend that you obtain the
publicly available version of pcnfsd as described in Section B. This
version already has the patch described in Section C.
If you are presently using a public version of pcnfsd, we recommend
that you either change to the version listed in Section B or apply the
patch described in Section C. (The version in Section B already contains
this patch.)
A. Obtain and install the appropriate patch according to the
instructions included with the patch.
Below is a list of the vendors who have reported to us as of the date
of this advisory. More complete information, including how to obtain
patches, is provided in the appendix of this advisory and reproduced
in the CA-96.xx.README file. We will update the README file as we
receive more information.
If your vendor's name is not on this list, please contact the vendor
directly.
Vendor or Source Status
---------------- ------------
BSDI BSD/OS Vulnerable. Patch available.
Hewlett Packard Vulnerable. Patch under development.
IBM AIX 3.2 Vulnerable. Patches available.
IBM AIX 4.1 Vulnerable. Patches available.
NEXTSTEP Vulnerable. Will be fixed in version 4.0.
SCO OpenServer 5 Vulnerable. Patch under development.
SCO UnixWare 2.1 Vulnerable. Patch under development.
SGI IRIX 5.3 Vulnerable. Patch under development.
SGI IRIX 6.2 Not vulnerable.
B. Until you are able to install the appropriate patch, we recommend
that you obtain a version of pcnfsd from one of the following
locations. This version already has the patch mentioned in
Section III.C and included in Appendix B.
ftp://ftp.cert.org/pub/tools/pcnfsd/pcnfsd.93.02.16-cert-dist.tar.Z
ftp://ftp.cert.dfn.de/pub/tools/net/pcnfsd/pcnfsd.93.02.16-cert-dist.tar.Z
MD5 (pcnfsd.93.02.16-cert-dist.tar.Z) = b7af99a07dfcf24b3da3446d073f8649
Build, install, and restart rpc.pcnfsd.
Ensure that the mode of the top-level pcnfsd spool directory is 755.
In this version of pcnfsd, the top level spool directory is
/usr/spool/pcnfs. To change this to mode 755, do the following as
root:
chmod 755 /usr/spool/pcnfs
C. Appendix B contains a patch for the two vulnerabilities described
in this advisory. Apply the patch using the GNU patch utility or
by hand as necessary. Rebuild, reinstall, and restart rpc.pcnfsd.
Set the mode of the top-level pcnfsd spool directory to 755.
For example, in the version of pcnfsd cited in Section B, the top
level spool directory is /usr/spool/pcnfs. To change this to mode
755, do the following as root:
chmod 755 /usr/spool/pcnfs
---------------------------------------------------------------------------
The CERT Coordination Center thanks Josh D., Ben G., and Alfred H. of
Avalon Security Research for providing information for this advisory.
We thank Wolfgang Ley of DFN-CERT for his help in understanding these
problems.
---------------------------------------------------------------------------
.........................................................................
Appendix A: Vendor Information
Current as of April 18, 1996
See CA-96.08.README for updated information.
Below is information we have received from vendors concerning the
vulnerability described in this advisory. If you do not see your vendor's
name, please contact the vendor directly for information.
Berkeley Software Design, Inc. (BSDI)
=====================================
The problem described in these vulnerabilities is present in all versions
of BSD/OS. There is a patch (our patch number U210-007) for our 2.1 version
of BSD/OS and associated products available from our patch and ftp servers
<patches@BSDI.> or ftp://ftp.BSDI.COM/bsdi/patches/patches-2.1/U210-007
Hewlett-Packard Company
=======================
Patches in process, watch for HP an security bulletin for this
vulnerability.
IBM Corporation
===============
See the appropriate release below to determine your action.
AIX 3.2
-------
Apply the following fixes to your system:
APAR - IX57623 (PTF - U442633)
APAR - IX56965 (PTF - U442638)
To determine if you have these PTFs on your system, run the following
commands:
lslpp -lB U442633
lslpp -lB U442638
AIX 4.1
-------
Apply the following fixes to your system:
APAR - IX57616
APAR - IX56730
To determine if you have these APARs on your system, run the following
commands:
instfix -ik IX57616
instfix -ik IX56730
To Order
--------
APARs may be ordered using FixDist or from the IBM Support Center.
For more information on FixDist, reference URL:
http://aix.boulder.ibm.com/pbin-usa/fixdist.pl/
or send e-mail to aixserv@austin.ibm.com with a subject of "FixDist".
IBM and AIX are registered trademarks of International Business Machines
Corporation.
NeXT Software, Inc.
===================
NEXTSTEP is vulnerable. This will be fixed in the 4.0 release of
OpenStep for Mach (aka NEXTSTEP 4.0, due out 2Q96).
The Santa Cruz Operation, Inc.
==============================
Patches for pcnfsd are currently being developed for the
following releases:
SCO OpenServer 5
SCO UnixWare 2.1.
These releases, as well as all prior releases, are vulnerable to
both issues mentioned in the advisory. Should you not need to use
pcnfs, SCO recommends that you not run pcnfsd. This can be done
by commenting out pcnfsd in the appropriate script that starts
pcnfsd, located in /etc/rc2.d.
The README file for this advisory will be updated when further patch
information is available.
Silicon Graphics Corporation
============================
pcnfsd was only released for IRIX 5.3 and IRIX 6.2.
SGI is producing patch1179 for IRIX 5.3.
IRIX 6.2 is not vulnerable.
.........................................................................
Appendix B: Patch Information
Here is the patch for pcnfsd_print.c. It is also available as:
ftp://ftp.cert.org/pub/tools/pcnfsd/pcnfsd_print.c.diffs
ftp://ftp.cert.dfn.de/pub/tools/net/pcnfsd/pcnfsd_print.c.diffs
MD5 (pcnfsd_print.c-diffs) = ec44046ff5c769aa5bf2d8d155b61f1f
---------------------------------CUT HERE---------------------------------
*** /tmp/T0a002c1 Fri Apr 5 13:14:50 1996
--- pcnfsd_print.c Fri Apr 5 13:14:46 1996
***************
*** 221,226 ****
--- 221,227 ----
{
int dir_mode = 0777;
int rc;
+ mode_t oldmask;
*sp = &pathname[0];
pathname[0] = '\0';
***************
*** 231,241 ****
/* get pathname of current directory and return to client */
(void)sprintf(pathname,"%s/%s",sp_name, sys);
(void)mkdir(sp_name, dir_mode); /* ignore the return code */
- (void)chmod(sp_name, dir_mode);
rc = mkdir(pathname, dir_mode); /* DON'T ignore this return code */
if((rc < 0 && errno != EEXIST) ||
- (chmod(pathname, dir_mode) != 0) ||
(stat(pathname, &statbuf) != 0) ||
!(statbuf.st_mode & S_IFDIR)) {
(void)sprintf(tempstr,
--- 232,242 ----
/* get pathname of current directory and return to client */
(void)sprintf(pathname,"%s/%s",sp_name, sys);
+ oldmask = umask(0);
(void)mkdir(sp_name, dir_mode); /* ignore the return code */
rc = mkdir(pathname, dir_mode); /* DON'T ignore this return code */
+ umask(oldmask);
if((rc < 0 && errno != EEXIST) ||
(stat(pathname, &statbuf) != 0) ||
!(statbuf.st_mode & S_IFDIR)) {
(void)sprintf(tempstr,
***************
*** 381,387 ****
** filter with the appropriate arguments.
**------------------------------------------------------
*/
! (void)run_ps630(new_pathname, opts);
}
/*
** Try to match to an aliased printer
--- 382,391 ----
** filter with the appropriate arguments.
**------------------------------------------------------
*/
! (void)sprintf(tempstr,
! "rpc.pcnfsd: ps630 filter disabled for %s\n",
pathname);
! msg_out(tempstr);
! return(PS_RES_FAIL);
}
/*
** Try to match to an aliased printer
---------------------------------CUT HERE---------------------------------
[ End of CERT Advisory ]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of CERT for the
information contained in this bulletin.
_______________________________________________________________________________
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