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CERT Advisory 117
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=============================================================================
CERT(sm) Advisory CA-96.12
Original issue date: June 26, 1996
Last revised: August 30, 1996
Information previously in the README was inserted
into the advisory.
A complete revision history is at the end of this file.
Topic: Vulnerability in suidperl
- -----------------------------------------------------------------------------
The CERT Coordination Center has received reports of a vulnerability in
systems that contain the suidperl program and that support saved
set-user-ID and saved set-group-ID. By exploiting this vulnerability,
anyone with access to an account on such a system may gain root access.
Saved set-user-IDs and set-group-IDs are sometimes referred to as POSIX
saved IDs. suidperl is also known as sperl followed by a version number,
as in sperl5.002.
Perl versions 4 and 5 can be compiled and installed in such a way that
they will be vulnerable on some systems. If you have installed the
suidperl or sperl programs on a system that supports saved set-user-ID and
set-group-ID, you may be at risk.
The CERT Coordination Center recommends that you first disable the
suidperl and sperl programs (Section III.A). If you need the
functionality, we further recommend that you either apply a patch for
this problem or install Perl version 5.003 (Section III.B). If neither
a patch nor a new version are viable alternatives, we recommend
installing the wrapper written by Larry Wall as a workaround for this
problem (Section III.C).
We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.
- -----------------------------------------------------------------------------
I. Description
On some systems, setuid and setgid scripts (scripts written in the
C shell, Bourne shell, or Perl, for example, with the set user or
group ID permissions enabled) are insecure due to a race condition in
the kernel. For those systems, Perl versions 4 and 5 attempt to work
around this vulnerability with a special program named suidperl, also
known as sperl. Even on systems that do provide a secure mechanism for
setuid and setgid scripts, suidperl may also be installed--although it
is not needed.
suidperl attempts to emulate the set-user-ID and set-group-ID
features of the kernel. Depending on whether the script is
set-user-ID, set-group-ID, or both, suidperl achieves this emulation
by first changing its effective user or group ID to that of the
original Perl script. suidperl then reads and executes the script as
that effective user or group. To do these user and group ID changes
correctly, suidperl must be installed as set-user-ID root.
On systems that support saved set-user-ID and set-group-ID, suidperl
does not properly relinquish its root privileges when changing its
effective user and group IDs.
II. Impact
On a system that has the suidperl or sperl program installed and
that supports saved set-user-ID and saved set-group-ID, anyone with
access to an account on the system can gain root access.
III. Solution
The command in Section A helps you determine if your system is
vulnerable and, if it is, optionally disables the suidperl and
sperl programs that it locates. After you have run this command
on all of your systems, your system will no longer be vulnerable.
If you find that your system is vulnerable, then you need to replace
the suidperl and sperl programs with new versions. Section B describes
how to do that.
Finally, Section C identifies a wrapper that can be used in place of
the suidperl program.
A. How to determine if your system is vulnerable
To determine if a system is vulnerable to this problem and to
disable the programs that are believed to be vulnerable, use the
following find command or a variant. Consult your local system
documentation to determine how to tailor the find program on your
system.
You will need to run the find command on each system you maintain
because the command examines files on the local disk only. Substitute
the names of your local file systems for FILE_SYSTEM_NAMES in the
example. Example local file system names are /, /usr, and /var.
You must do this as root.
Note that this is one long command, though we have separated
it onto three lines using back-slashes.
find FILE_SYSTEM_NAMES -xdev -type f -user root \
\( -name 'sperl[0-9].[0-9][0-9][0-9]' -o -name \
'suidperl' \) -perm -04000 -print -ok chmod ug-s '{}' \;
This command will find all files on a system that are
- only in the file system you name (FILE_SYSTEM_NAMES -xdev)
- regular files (-type f)
- owned by root (-user root)
- named appropriately (-name 'sperl[0-9].[0-9][0-9][0-9]'
-o -name 'suidperl')
- setuid root (-perm -04000)
Once found, those files will
- have their names printed (-print)
- have their modes changed, but only if you type `y'
in response to the prompt (-ok chown ug-s '{}' \;)
B. Obtain and install the appropriate patch according to the
instructions included with the patch.
Vendor patches
--------------
You may be vulnerable if your vendor supports saved set-user-ID
and set-group-ID and ships suidperl or sperl. You need to get
a patched version from your vendor. Appendix A contains
information provided by the following vendors. If you vendor is not on
this list, please contact the vendor directly.
Vendor or Source
----------------
Apple Computer, Inc.
Data General Corp.
Digital Equipment Corp.
FreeBSD, Inc.
Hewlett-Packard Company
IBM Corporation
Linux
NEC
Open Software Foundation
Sony Corporation
X.org
Until you can install a patch, we recommend disabling suidperl.
The find command above will help you do that. If you need
suidperl or sperl, an alternative is to install the wrapper
described in Section C.
Source code patches
-------------------
If you have installed Perl from source code, you should install
source code patches. Patches are available from the CPAN
(Comprehensive Perl Archive Network) archives.
Patch for Perl Version 4:
File src/fixsuid4-0.pat
MD5 Checksum af3e3c40bbaafce134714f1381722496
Patch for Perl Version 5:
File src/fixsuid5-0.pat
MD5 Checksum 135c96ee400fd37a38a7ef37edd489e9
In addition, Perl version 5.003 contains this patch, so installing
it on your system also addresses this vulnerability. Perl 5.003 is
available from the CPAN archives. Here are the specifics:
File src/5.0/perl5.003.tar.gz
MD5 Checksum b1bb23995cd25e5b750585bfede0e8a5
The CPAN archives can be found at the following locations:
CPAN master site
ftp://ftp.funet.fi/pub/languages/perl/CPAN/
Africa
ftp://ftp.is.co.za/programming/perl/CPAN/
Asia
ftp://dongpo.math.ncu.edu.tw/perl/CPAN/
ftp://ftp.lab.kdd.co.jp/lang/perl/CPAN/
Australasia
ftp://coombs.anu.edu.au/pub/perl/
ftp://ftp.mame.mu.oz.au/pub/perl/CPAN/
ftp://ftp.tekotago.ac.nz/pub/perl/CPAN/
Europe
ftp://ftp.arnes.si/software/perl/CPAN/
ftp://ftp.ci.uminho.pt/pub/lang/perl/
ftp://ftp.cs.ruu.nl/pub/PERL/CPAN/
ftp://ftp.demon.co.uk/pub/mirrors/perl/CPAN/
ftp://ftp.funet.fi/pub/languages/perl/CPAN/
ftp://ftp.ibp.fr/pub/perl/CPAN/
ftp://ftp.leo.org/pub/comp/programming/languages/perl/CPAN/
ftp://ftp.pasteur.fr/pub/computing/unix/perl/CPAN/
ftp://ftp.rz.ruhr-uni-bochum.de/pub/programming/languages/perl/CPAN/
ftp://ftp.sunet.se/pub/lang/perl/CPAN/
ftp://ftp.switch.ch/mirror/CPAN/
ftp://unix.hensa.ac.uk/mirrors/perl-CPAN/
North America
ftp://ftp.cis.ufl.edu/pub/perl/CPAN/
ftp://ftp.delphi.com/pub/mirrors/packages/perl/CPAN/
ftp://ftp.sedl.org/pub/mirrors/CPAN/
ftp://ftp.sterling.com/programming/languages/perl/
ftp://ftp.uoknor.edu/mirrors/CPAN/
ftp://uiarchive.cso.uiuc.edu/pub/lang/perl/CPAN/
C. If you need setuid or setgid Perl scripts and are unable to apply
the source code patches listed in Section B, we suggest that you
retrieve Larry Wall's fixsperl script noted below. fixsperl is a
script that replaces the suidperl and sperl programs with a wrapper
that eliminates the vulnerability. The script is available from the
CPAN archives as
File src/fixsperl-0
MD5 Checksum f13900d122a904a8453a0af4c1bdddc6
Note that this script should be run one time, naming every suidperl
or sperl file on your system. If you add another version of
suidperl or sperl to your system, then you must run fixsperl
on those newly installed versions.
.........................................................................
Appendix A: Vendor Information
Below is information we have received from vendors concerning the
vulnerability described in this advisory. If you do not see your vendor's
name, please contact the vendor directly for information.
Apple Computer, Inc.
====================
A/UX 3.1.1 and earlier support saved set-{user,group}-ids.
A/UX 3.1.1 and earlier do not have Perl as part of the standard
product.
Data General Corporation
========================
Data General does support saved set-user-IDs and set-group-IDs on
DG/UX.
Data General does not ship suidperl or sperl* with DG/UX.
Digital Equipment Corporation
=============================
Digital UNIX and Digital's ULTRIX Operating systems do support
saved suid and saved guid in the process context.
Digital does not ship Perl with any operating system.
FreeBSD, Inc.
=============
This information is taken from FreeBSD advisory SA-96:12.
For the complete text of the advisory, please refer to
ftp://freebsd.org/pub/CERT/patches/SA-96:12/
This vulnerability is present on all systems with the
_POSIX_SAVED_IDS functionality extension where suidperl
has been installed.
One may 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
Other information:
*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 above.
Hewlett-Packard Company
=======================
HP/UX versions 8.X, 9.X, and 10.X all support saved set-user-id.
None of HP/UX versions 8.X, 9.X, and 10.X have Perl as part of the
standard product.
IBM Corporation
===============
AIX versions 3.2.5 and 4.X support saved set-user-id.
AIX versions 3.2.5 and 4.X do not have Perl as part of the standard
product. However, the SP2's PSSP software does contain suidperl, but
the program is not installed with the setuid bit set.
Linux
=====
Linux 1.2 and 2.0 support saved set-user-id.
Most distributions of Linux provide suidperl and sperl.
The fixsperl script works on linux, and it is recommended that this
fix be applied until a new Perl release is made.
NEC
===
OS Support Saved Sets? Provide suidperl?
-------------------------------------------------------------------
UX/4800 yes no
EWS-UX/V (Rel4.2MP) yes no
UP-UX/V (Rel4.2MP) yes no
EWS-UX/V (Rel4.2) yes no
Open Software Foundation
========================
OSF/1 1.3 or later support saved set-user-id
OSF/1 1.3 or later does not have Perl as part of the standard
product.
Sony Corporation
================
NEWS-OS 4.X does not support saved set-user-id and therefore any
version of Perl on that system is not vulnerable.
NEWS-OS 6.X does support saved set-user-id.
X.org
=====
None of X.org's development systems are vulnerable to the saved
set-user-IDs and set-group-IDs problems, and suidperl is not shipped
with either of our products.
- ---------------------------------------------------------------------------
The CERT Coordination Center staff thanks Paul Traina, Larry Wall, Eric
Allman, Tom Christiansen, and AUSCERT for their support in the development
of this advisory.
- ---------------------------------------------------------------------------
If you believe that your system has been compromised, contact the CERT
Coordination Center or your representative in the Forum of Incident
Response and Security Teams (FIRST).
We strongly urge you to encrypt any sensitive information you send by
email. The CERT Coordination Center can support a shared DES key and PGP.
Contact the CERT staff for more information.
Location of CERT PGP key:
ftp://info.cert.org/pub/CERT_PGP.key
CERT Contact Information
- ------------------------
Email cert@cert.org
Phone +1 412-268-7090 (24-hour hotline)
CERT personnel answer 8:30-5:00 p.m. EST
(GMT-5)/EDT(GMT-4), and are on call for
emergencies during other hours.
Fax +1 412-268-6989
Postal address
CERT Coordination Center
Software Engineering Institute
Carnegie Mellon University
Pittsburgh PA 15213-3890
USA
CERT publications, information about FIRST representatives, and other
security-related information are available for anonymous FTP from
http://www.cert.org/
ftp://info.cert.org/pub/
CERT advisories and bulletins are also posted on the USENET newsgroup
comp.security.announce
To be added to our mailing list for CERT advisories and bulletins, send your
email address to
cert-advisory-request@cert.org
Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for non-commercial purposes and the copyright statement is
included.
CERT is a service mark of Carnegie Mellon University.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history
Aug. 30, 1996 Information previously in the README was inserted into the
advisory.
July 01, 1996 Appendix, FreeBSD - added an entry for this vendor.
June 27, 1996 Appendix, NEC - added an entry for this vendor.
June 26, 1996 Appendix, Digital - added an entry for this vendor.
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