=============================================================================

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:        http://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 

     @@ -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 

     @@ -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);



=============================================================================

FreeBSD, Inc.



Web Site:                       http://www.freebsd.org/

Confidential contacts:          security-officer@freebsd.org

PGP Key:                        http://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.

=============================================================================