From: mea culpa (jerichoat_private)
Date: Tue Aug 18 1998 - 17:21:28 PDT

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    Forwarded From: RSI Advise <adviseat_private>
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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
    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
                   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:
    --- [LINUX PATCH] ---------------------------------------------------------
    Solution:      Working in conjunction with Patrick Volkerding and the
                   Slackware Linux development staff, RSI has produced the
                   following patches:
                   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:
    -	if(strpbrk(s, ";|&<>`'#!?*()[]^/") != NULL)
    +       if (strspn(s, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ-_=:+1234567890@%,.")
                   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. 
    +        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);
    -	(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)) {
    --- [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: adviseat_private
    FTP: ftp://ftp.repsec.com
    WWW: http://www.repsec.com
    Version: 2.6.2
    Copyright August 1998  RepSec, Inc.
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    Mark Zielinski
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