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CERT Advisory 134
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=============================================================================
CERT* Advisory CA-97.02
Original issue date: January 7, 1997
Last revised: April 3, 1997
Updates section - Added a note that the vulnerability is being
exploited.
Topic: HP-UX newgrp Buffer Overrun Vulnerability
- -----------------------------------------------------------------------------
The text of this advisory was originally released on December 3, 1996, as
AA-96.16.HP-UX.newgrp.Buffer.Overrun.Vulnerability, developed by
AUSCERT. Because of the seriousness of the problem, we are reprinting the
AUSCERT advisory here with their permission. Only the contact information
at the end has changed: AUSCERT contact information has been replaced with
CERT/CC contact information.
We will update this advisory as we receive additional information.
Look for it in an "Updates" section at the end of the advisory.
===========================================================================
AUSCERT has received information that a vulnerability exists in the
newgrp(1) program under HP-UX 9.x and 10.x.
This vulnerability may allow local users to gain root privileges.
Exploit information involving this vulnerability has been made publicly
available.
Currently there are no vendor patches available that address this
vulnerability. AUSCERT recommends that sites take the steps outlined in
section 3 as soon as possible.
This advisory will be updated as more information becomes available.
- ----------------------------------------------------------------------------
1. Description
AUSCERT has received information that a vulnerability exists in the
HP-UX newgrp(1) program. The newgrp command is used to change a users
group identification, and is installed by default.
Due to insufficient bounds checking on arguments which are supplied
by users, it is possible to overwrite the internal stack space of the
newgrp program while it is executing. By supplying a carefully
designed argument to the newgrp program, intruders may be able to
force newgrp to execute arbitrary commands. As newgrp is setuid
root, this may allow intruders to run arbitrary commands with root
privileges.
This vulnerability is known to affect both HP-UX 9.x and 10.x.
By default, newgrp is located in /bin under HP-UX 9.x and in
/usr/bin under HP-UX 10.x.
Exploit information involving this vulnerability has been made
publicly available.
2. Impact
Local users may gain root privileges.
3. Workarounds/Solution
AUSCERT recommends that sites limit the possible exploitation of this
vulnerability by immediately removing the setuid permissions as stated
in Section 3.1. If the newgrp command is required, AUSCERT recommends
the newgrp wrapper program given in Section 3.2 be installed.
AUSCERT recommends that official vendor patches be installed when
they are made available. See the Updates section for information
about availability of patches.
3.1 Remove setuid and non-root execute permissions
To prevent the exploitation of the vulnerability described in the
advisory, AUSCERT recommends that the setuid permissions be removed from
the newgrp program immediately. As the newgrp program will no
longer work for non-root users, it is recommended that the execute
permissions also be removed. Before doing so, the original permissions
for newgrp should be noted as they will be needed if sites choose to
install the newgrp wrapper program (Section 3.2).
For HP-UX 9.x:
# ls -l /bin/newgrp
-r-sr-xr-x 1 root sys 16384 Dec 2 13:45 /bin/newgrp
# chmod 500 /bin/newgrp
# ls -l /bin/newgrp
-r-x------ 1 root sys 16384 Dec 2 13:45 /bin/newgrp
For HP-UX 10.x:
# ls -l /usr/bin/newgrp
-r-sr-xr-x 1 root sys 12288 Dec 2 13:27 /usr/bin/newgrp
# chmod 500 /usr/bin/newgrp
# ls -l /usr/bin/newgrp
-r-x------ 1 root sys 12288 Dec 2 13:27 /usr/bin/newgrp
Note that this will remove the ability for any non-root user to run the
newgrp program.
3.2 Install newgrp wrapper
AUSCERT has developed a wrapper to help prevent programs from being
exploited using the vulnerability described in this advisory. This
wrapper, including installation instructions, can be found at:
ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper.c
This replaces the newgrp program with a wrapper which checks the
length of the command line arguments passed to it. If an argument
exceeds a certain predefined value (MAXARGLEN), the wrapper exits
without executing the newgrp command. The wrapper program can also
be configured to syslog any failed attempts to execute newgrp with
arguments exceeding MAXARGLEN. For further instructions on using
this wrapper, please read the comments at the top of overflow_wrapper.c.
When compiling overflow_wrapper.c for use with HP-UX newgrp, AUSCERT
recommends defining MAXARGLEN to be 16.
The MD5 checksum for Version 1.0 of overflow_wrapper.c is:
MD5 (overflow_wrapper.c) = f7f83af7f3f0ec1188ed26cf9280f6db
AUSCERT recommends that until vendor patches can be installed, sites
requiring the newgrp functionality apply this workaround.
- ----------------------------------------------------------------------------
AUSCERT thanks Hewlett-Packard for their continued assistance and technical
expertise essential for the production of this advisory. AUSCERT also
thanks Information Technology Services of the University of Southern
Queensland for their assistance.
- ----------------------------------------------------------------------------
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
* Registered U.S. Patent and Trademark Office.
This file: ftp://info.cert.org/pub/cert_advisories/CA-97.02.hp_newgrp
http://www.cert.org
click on "CERT Advisories"
=============================================================================
UPDATES
April 4, 1997
- -------------
The CERT/CC has received reports that the vulnerability described in this
advisory is being exploited.
January 14, 1997
- ----------------
All HP patches are now available, see HEWLETT-PACKARD SECURITY BULLETIN:
#00048, issued on 09 January 1997:
PHCO_9603 for all platforms with HP-UX releases 9.X
PHCO_9604 for all platforms with HP-UX releases 10.00/10.01
PHCO_9605 for all platforms with HP-UX releases 10.10/10.20
Fixing the problem
The vulnerability can be eliminated from HP-UX releases 9.X and
10.X by applying the appropriate patch.
Recommended solution
1. Determine which patch are appropriate for your operating
system.
2. Hewlett-Packard's HP-UX patches are available via email
and the World Wide Web
To obtain a copy of the Hewlett-Packard SupportLine email
service user's guide, send the following in the TEXT PORTION
OF THE MESSAGE to support@us.external.hp.com (no Subject
is required):
send guide
The users guide explains the HP-UX patch downloading process
via email and other services available.
World Wide Web service for downloading of patches
is available via our URL:
(http://us.external.hp.com)
3. Apply the patch to your HP-UX system.
4. Examine /tmp/update.log (9.X), or /var/adm/sw/swinstall.log
(10.X), for any relevant WARNING's or ERROR's.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history
Apr. 04, 1997 Updates - added note that the vulnerability is being exploited.
Jan. 14, 1997 Updates - added patch information.
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