RSI.0008.08-18-98.ALL.RPC_PCNFSD

[advise () enigma repsec com (RSI Advise)]

RSI.0008.08-18-98.ALL.RPC_PCNFSD



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                   Repent Security Incorporated, RSI
                       [ http://www.repsec.com ]


                       *** RSI ALERT ADVISORY ***


--- [CREDIT] --------------------------------------------------------------

'Bermuda Brian': Research and development
Mark Zielinski : Author of advisory


--- [SUMMARY] -------------------------------------------------------------

Announced:     July 14, 1998
Report code:   RSI.0008.08-18-98.ALL.RPC_PCNFSD
Report title:  All rpc.pcnfsd
Vulnerability: Please see the details section
Vendor status: IBM contacted on August 3, 1998
               Hewlett Packard contacted on August 3, 1998
               Sun Microsystems contacted on August 3, 1998
               Slackware contacted on August 3, 1998
Patch status:  Linux and AIX patch information is provided below
Platforms:     Vulnerable:

               AIX: 4.0, 4.1, 4.2, 4.3
               HP-UX: 7.x, 8.x, 9.x, 10.x, 11.x
               SunOS: 4.1.3, 4.1.4
               Solaris: 2.3, 2.4, 2.5, 2.5.1, 2.6
               Redhat Linux: 4.0, 4.1, 4.2, 5.0, 5.1
               Slackware Linux: 3.0, 3.1, 3.2, 3.3, 3.4, 3.5
               OSF: 3.2

               Not vulnerable:

               OpenBSD, FreeBSD, NetBSD, BSDI

Reference:     http://www.repsec.com/advisories.html
Impact:        If exploited, an attacker could potentially compromise
               root access both locally and remotely on your server


--- [DETAILS] -------------------------------------------------------------

Description:   PCNFSD is a Remote Procedure Call used by NFS clients.
               This service provides username and password authentication
               for networked computers which have installed NFS client
               software.


Problem:       Two vulnerabilities are covered in this advisory which
               both allow root access to be compromised.

               Vulnerable functions:
               ~~~~~~~~~~~~~~~~~~~~~

               A. pr_init ()    : This function will create a spool
                                  directory for a client.  When
                                  passing data to this function, it
                                  calls secure () attempting to find
                                  any insecure characters.

                                  The list of characters that suspicious ()
                                  checks for are: ";|&<>`'!?*()[]^/".

                                  By sending a "." as the printer name,
                                  rpc.pcnfsd will attempt to make that
                                  directory and set the mode to 777.
                                  By doing this, an attacker sets the
                                  main spool directory used by rpc.pcnfsd
                                  to world writeable.

                                  To exploit this, an attacker could
                                  locally set a symbolic link from
                                  /var/spool/pcnfsd/printername to
                                  any other file on the system.

                                  Calling pr_init () with the name
                                  of the symbolically linked file will
                                  force rpc.pcnfsd to follow the symlink
                                  and change the destination file to mode
                                  777.

               B. run_ps630 ()  : Upon system bootup, rpc.pcnfsd is
                                  started from the system rc files
                                  which are executed from the / directory.

                                  Because of this, rpc.pcnfsd will
                                  attempt to function out of the root
                                  directory (/).

                                  When run_ps630 () is called,
                                  it calls suspicious () to check
                                  for any insecure characters.

                                  The list of characters that secure ()
                                  checks for are: ";|&<>`'!?*()[]^/".

                                  If it detects that none of these
                                  characters are being used, it will
                                  call strcat () to append the data
                                  to a buffer and then run the
                                  data contained inside it with
                                  system ().

                                  By sending a \ncommand\n as the
                                  printer, "." as the spool
                                  directory, and setting your client
                                  options to "d", arbitary commands
                                  can be executed remotely on the
                                  server as root.

               * Note           : AIX is not vulnerable to problem A,
                                  and HP is only vulnerable to function
                                  A in HP-UX 9.0, 10.0.


--- [FIX] -----------------------------------------------------------------

Solution:      Disable rpc.pcnfsd until an appropriate patch is
               released for your operating system.


--- [AIX PATCH] -----------------------------------------------------------

               AIX users: IBM has provided the following patches in
               reponse to this vulnerability:

               APAR 4.1.x: IX81505
               APAR 4.2.x: IX81506
               APAR 4.3.x: IX81507

               Until the official APARs are available, a temporary
               fix can be downloaded via anonymous ftp from:

               ftp://aix.software.ibm.com/aix/efixes/security/pcnfsd.tar.Z


--- [LINUX PATCH] ---------------------------------------------------------

Solution:      Working in conjunction with Patrick Volkerding and the
               Slackware Linux development staff, RSI has produced the
               following patches:

               ftp://ftp.repsec.com/pub/repsec/0008.patch1

               WARNING! The code quoted below is only fragments of each
               patch! You must download each patch for it to work correctly.

               0008.patch1 replaces the character set that is considered
               suspicious and replaces it with a list of characters that
               are allowed. The following two lines show the change:

[snip...]

-       if(strpbrk(s, ";|&<>`'#!?*()[]^/") != NULL)

[snip...]

+       if (strspn(s, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_=:+1234567890@%,.")

[snip...]

               ---

               ftp://ftp.repsec.com/pub/repsec/0008.patch2

               0008.patch2 replaces the vulnerable code by removing the
               chmod call, and utilizing umask. The following code fragments
               have been stripped out of the patch to show the vulnerable
               pieces of code and the relevant fix.

[snip...]

+        oldumask = umask(0);
+        (void)sprintf(pathname,"%s/%s",sp_name, sys);
+        (void)mkdir(sp_name, dir_mode); /* ignore the return code */
+        rc = mkdir(pathname, dir_mode); /* DON'T ignore this return code */
+        umask(oldumask);

[snip...]

-       (void)chmod(sp_name, dir_mode);
        if((rc < 0 && errno != EEXIST) ||
-          (chmod(pathname, dir_mode) != 0) ||
           (stat(pathname, &statbuf) != 0) ||
           !(statbuf.st_mode & S_IFDIR)) {
           (void)sprintf(tempstr,


--- [OTHER PATCHES] -------------------------------------------------------

               SunOS, Solaris, HPUX, and OSF users should wait
               for their respective vendor to provide a patch.


---------------------------------------------------------------------------

Repent Security Incorporated (RSI)
13610 N. Scottsdale Rd.
Suite #10-326
Scottsdale, AZ 85254

E-Mail: advise () repsec com
FTP: ftp://ftp.repsec.com
WWW: http://www.repsec.com

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