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FreeBSD-SA-96:12              Security Advisory
                      FreeBSD, Inc.

Topic:    security compromise from perl (suidperl) utility

Category:  core and ports
Module:    perl
Announced:  1996-06-28
Affects:  FreeBSD 2.0, 2.0.5, 2.1, 2.1-stable, and 2.2-current
Corrected:  2.1-stable and 2.2-current as of 1996-06-03
FreeBSD only:  no

Patches:  ftp://freebsd.org/pub/CERT/patches/SA-96:12/

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

I.   Background    

     FreeBSD ships perl version 4 as part of the base level system,
     in addition, a port for perl version 5 is also provided with
     a similar vulnerability.  The vulnerability is specific to the
     suidperl flavors of perl installed on the system.

     This problem is present in all source code and binary
     distributions of FreeBSD version 2.0.5 and later released
     before 1996-05-21.  This problem is not present in FreeBSD
     2.0 and earlier versions of FreeBSD.

II.  Problem Description

     The authors of perl provide a "suidperl" program for proper
     processing of setuid perl scripts on systems where race
     conditions where setuid scripts could be exploited to gain
     unauthorized access.  FreeBSD installs this suidperl program
     (and a link) as part of the standard installation.  However,
     privilege processing done by this program does not take into
     account recent functionality extensions in the seteuid/setegid
     system calls.


III. Impact

     This vulnerability can only be exploited by users with a valid
     account on the local system to easily obtain superuser access.

     This vulnerability is present on all systems with the
     _POSIX_SAVED_IDS functionality extension where suidperl
     has been installed.


IV. Workaround

     One may simply disable the setuid bit on all copies of the setuid
     version of perl.  This will close the vulnerability but render
     inoperable setuid perl scripts.  No software currently shipping
     as part of FreeBSD relies on this functionality so the impact is
     only to third party software.

     As root, execute the commands:

   # chmod 111 /usr/bin/suidperl
   # chmod 111 /usr/bin/sperl4.036

     In addition, if you have installed the perl5 port:
   # chmod 111 /usr/local/bin/suidperl
   # chmod 111 /usr/local/bin/sperl5.001

     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/bin/s*perl*
   ---x--x--x  2 root  bin  307200 Jun  1 17:16 /usr/bin/sperl4.036
   ---x--x--x  2 root  bin  307200 Jun  1 17:16 /usr/bin/suidperl

     and for the perl5 port:

   # ls -l /usr/local/bin/s*perl*
   ---x--x--x  2 root  bin  397312 Jan 22 15:15 /usr/local/bin/sperl5.001
   ---x--x--x  2 root  bin  397312 Jan 22 15:15 /usr/local/bin/suidperl


V. Solution

     *NOTE* A patch for perl is available directly from Larry Wall
     (the author of perl) which solves this vulnerability in a
     different fashion than the FreeBSD patches.  You may apply
     either the FreeBSD patches, or Larry's patches, or both.
     The patches solve the problem via two different mechanisms.

     Patches are available which eliminate this vulnerability.
     The following patch should be applied to the system sources and
     suidperl should be rebuilt and reinstalled.

     Apply the patch, then:
  # cd /usr/src/gnu/usr.bin/perl/sperl
  # make depend
  # make all
  # make install

     A similar patch is also available for the perl5 port.
     Apply the following patch by moving it into the patch
     directory for the port distribution and rebuilding and
     installing perl5:

  # cd /usr/ports/lang/perl5
  # cp <location of new patches>/patch-a[ab] patches
  # make all
  # make install

     NOTE: These patches do NOT solve the vulnerability for FreeBSD 2.0
     or 2.0.5.  These only solve the problem for 2.1 and later.
     Patches specific to FreeBSD 2.0 and 2.0.5 are available at
     the URL listed at the top of this file.


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