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=============================================================================
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: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris Exp $
     + * $Id: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris 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: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris Exp $
     + * $Id: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris 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: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris Exp $
     + * $Id: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris 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: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris Exp $
     + * $Id: FreeBSD-SA-96:15.ppp.asc,v 1.1 2001/09/02 00:04:38 kris 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);
     
=============================================================================
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.
=============================================================================

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