CERT Advisory CA-96.19 - Vulnerability in expreserve

[cert-advisory () cert org (CERT Advisory)]

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CERT(sm) Advisory CA-96.19
August 15, 1996

Topic: Vulnerability in expreserve
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            *** 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.

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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

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The CERT Coordination Center thanks all the vendors who provided input
for this advisory.
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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).

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The CERT Coordination Center can support a shared DES key and PGP. Contact
the CERT staff for more information.

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         ftp://info.cert.org/pub/CERT_PGP.key

CERT Contact Information
- ------------------------
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Copyright 1996 Carnegie Mellon University
This material may be reproduced and distributed without permission provided
it is used for noncommercial purposes and the copyright statement is
included.

CERT is a service mark of Carnegie Mellon University.

This file: ftp://info.cert.org/pub/cert_advisories/CA-96.19.expreserve
           http://www.cert.org
               click on "CERT Advisories"



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