__________________________________________________________
The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
Vulnerability in expreserve
August 15, 1996 17:00 GMT Number G-39
______________________________________________________________________________
PROBLEM: A vulnerability in the expreserve utility allows users to
overwrite any file on a system.
PLATFORM: Many UNIX variants; see vendor information in bulletin below.
DAMAGE: By exploiting this vulnerability, users with access to an
account on the system can gain root access.
SOLUTION: Apply the appropriate vendor patches stated in the bulletin
below.
______________________________________________________________________________
VULNERABILITY This vulnerability is not new, and is widely known.
ASSESSMENT: Exploitation scripts are publicly available.
______________________________________________________________________________
[Begin CERT Bulletin]
=============================================================================
CERT(sm) Advisory CA-96.19
August 15, 1996
Topic: Vulnerability in expreserve
------------------------------------------------------------------------------
*** This advisory supersedes CA-93:09 and CA-93:09a. ***
The CERT Coordination Center has received reports of a vulnerability in
expreserve. Though this is not a new vulnerability, it is one that is widely
known and that many users have not yet patched. The CERT/CC team recommends
that you patch your system as soon as possible, as exploitation scripts are
publicly available. Appendix A contains the information we have received from
vendors. Until you can install a patch, you should apply the workaround in
Section III below.
As we receive additional information relating to this advisory, we will place
it in
ftp://info.cert.org/pub/cert_advisories/CA-96.19.README
We encourage you to check our README files regularly for updates on
advisories that relate to your site.
------------------------------------------------------------------------------
I. Description
Expreserve is a utility that preserves the state of a file being edited
by vi(1) or ex(1) when an edit session terminates abnormally or when the
system crashes. Expreserve has a vulnerability that allows users to
overwrite any file on the system. Exploitation scripts are publicly
available.
II. Impact
By exploiting this vulnerability, users with access to an account on the
system can readily gain root privileges.
III. Solution
A. Apply a patch or workaround provided by your vendor.
Below is a summary list of the vendors who have provided information,
which we have placed in Appendix A of this advisory. If your vendor's
name is not on this list, please contact the vendor directly.
Berkeley Software Design, Inc.
Cray Research
Data General Corporation
Digital Equipment Corporation
Hewlett-Packard Company
IBM Corporation
NeXT Software, Inc.
Open Software Foundation
The Santa Cruz Operation, Inc.
Sun Microsystems, Inc.
B. Until you are able to apply a patch or workaround, we recommend
that you remove the execute permissions on the existing
/usr/lib/expreserve program. Do this as root:
% /usr/bin/chmod a-x /usr/lib/expreserve
This workaround disables expreserve functionality. The result of this
workaround is that if vi(1) or ex(1) is running, and the sessions are
interrupted, the files being edited will not be preserved and all
edits not explicitly saved by the users will be lost. Encourage users
to save their files often.
.........................................................................
Appendix A: Vendor Information
Current as of August 15, 1996
See CA-96.19.README for updated 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.
Berkeley Software Design, Inc.
==============================
BSD/OS is not vulnerable to this problem. We ship the
current Keith Bostic nvi which does not use the old expreserve
scheme to save files (it uses the 4.4BSD-style 1777 tmp
directories to store user tmp files in /var/tmp owned by
the user and therefore doesn't require a setuid scheme to
recover them).
Cray Research
=============
We have fixed this problem at Cray Research in Unicos version 7.0.
Data General Corporation
========================
The binary /usr/lib/expreserve is not a setuid program on DG/UX,
any flavor. We are not, therefore, vulnerable to the exploitation
described. Nevertheless, the suggested change has been made and
will be included in subsequent releases of DG/UX.
Digital Equipment Corporation
=============================
This reported problem is not present for Digital's ULTRIX or
Digital UNIX Operating Systems Software.
Source:
Digital Equipment Corporation
Software Security Response Team
Copyright (c) Digital Equipment Corporation 1996.
All rights reserved.
8/13/96 - DIGITAL EQUIPMENT CORPORATION
Hewlett-Packard Company
=======================
Hewlett-Packard recommends that all customers concerned with the
security of their HP-UX systems either apply the appropriate
patch or perform the actions described below as soon as possible.
The vulnerability can be eliminated from releases 9.X of HP-UX
by applying a patch:
Apply patch PHCO_6363 (series 700/800, HP-UX 9.x), or
PHCO_7833 (series 300/400, HP-UX 9.x), or
perform the actions described below in releases of HP-UX prior
to 9.X, and in 10.X)
Since some patches will not be made available on some releases of HP-UX
(e.g., prior to 9.X, and now 10.0X), affected systems can be protected by
system administrators.
They should:
$ su root
# chmod 0555 /usr/lib/expreserve
In the case of 10.X systems execute the following to affect the link
target:
$ su root
# chmod 0555 /usr/lbin/expreserve
The default permission for the file /usr/lib/expreserve (or on HP-UX 10.X
/usr/lbin/expreserve) needs only minimal privileges. If the patches
mentioned above are applied the vulnerability cannot be exploited.
Hewlett-Packard Security Bulletin #HPSBUX9607-033, dated July 18, 1996
contains more details. This bulletin is available from
http://us.external.hp.com/news/
ftp://info.cert.org/pub/vendors/hp/
IBM Corporation
===============
AIX versions 3.2.5, 4.1, and 4.2 are not vulnerable to this
particular problem.
IBM and AIX are registered trademarks of International Business
Machines Corporation.
NeXT Software, Inc.
===================
This problem was fixed in or before release 3.3 of NeXTstep.
Open Software Foundation
========================
OSF's OSF/1 R1.3 is not effected by this vulnerability.
The Santa Cruz Operation, Inc.
==============================
SCO Operating Systems are not vulnerable to this problem.
Sun Microsystems, Inc.
======================
System Patch ID Filename MD5 Checksum
- ------ -------- --------------- -----------
SunOS 101080-01 101080-01.tar.Z 53c8a5c4eee770924560c5fc100542a3
Solaris 2.0 101119-01 101119-01.tar.Z No longer available
Solaris 2.1 101089-01 101089-01.tar.Z No longer available
Solaris 2.2 101090-01 101090-01.tar.Z e9ff98823abbc75d95410a0cb7856644
Solaris 2.3
Solaris 2.4 102756-01 102756-01.tar.Z 61f4a48ddba41ae1c27e70b84f4c8d87
Solaris 2.4_x86 102757-01 102757-01.tar.Z 1f2b7f3824565ef849eb3c4677567399
----------------------------------------------------------------------------
The CERT Coordination Center thanks all the vendors who provided input
for this advisory.
----------------------------------------------------------------------------
[End CERT Bulletin]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of CERT and all the vendors who
provided input for the information contained in this bulletin.
_______________________________________________________________________________
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LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC)
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G-32: HP-UX Vulnerabilities in expreserve, rpc.pcnfsd, rpc.statd
G-33: rdist vulnerability
G-34: HP-UX Vulnerabilities (netttune, SAM remote admin)
G-35: SUN Microsystems Solaris vold Vulnerability
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