HP-UX newgrp Buffer Overrun Vulnerability

Original issue date: January 7, 1997
Last revised: September 26, 1997
Updated copyright statement

A complete revision history is at the end of this file.

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:


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.


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:


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.

Copyright 1997 Carnegie Mellon University.

Revision History
Sep. 26, 1997 Updates - added copyright statement
Apr. 04, 1997 Updates - added note that the vulnerability is being exploited.
Jan. 14, 1997 Updates - added patch information.