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CERT(sm) Advisory CA-96.13
Original issue date: July 9, 1996
Last revised: August 30, 1996
              Removed references to the advisory README file.

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

Topic: Vulnerability in the dip program
- -----------------------------------------------------------------------------

The CERT Coordination Center has received several reports of exploitations of
a vulnerability in the dip program on Linux systems. The dip program is
shipped with most versions of the Linux system; and versions up to and
including version 3.3.7n are vulnerable. An exploitation script for Linux
running on X86-based hardware is publicly available. Although exploitation
scripts for other architectures and operating systems have not yet been found,
we believe that they could be easily developed.

The CERT Coordination Center recommends that you disable dip and re-enable it
only after you have installed a new version. Section III below describes how
to do that.

We will update this advisory as we receive additional information.
Please check advisory files regularly for updates that relate to your site.

- -----------------------------------------------------------------------------

I.   Description

     dip is a freely available program that is included in most distributions
     of Linux. It is possible to build it for and use it on other UNIX systems.

     The dip program manages the connections needed for dial-up links such
     as SLIP and PPP. It can handle both incoming and outgoing connections.
     To gain access to resources it needs to establish these IP connections,
     the dip program must be installed as set-user-id root.

     A vulnerability in dip makes it possible to overflow an internal buffer
     whose value is under the control of the user of the dip program. If this
     buffer is overflowed with the appropriate data, a program such as a
     shell can be started. This program then runs with root permissions on the
     local machine.

     Exploitation scripts for dip have been found running on Linux systems for
     X86 hardware. Although exploitation scripts for other architectures
     and operating systems have not yet been found, we believe that they could
     be easily developed.

II.  Impact

     On a system that has dip installed as set-user-id root, anyone with
     access to an account on that system can gain root access.

III. Solution

     Follow the steps in Section A to disable your currently installed version
     of dip. Then, if you need the functionality that dip provides, follow the
     steps given in Section B.

     A.  Disable the presently installed version of dip.
         As root,
                chmod 0755 /usr/sbin/dip

         By default, dip is installed in the /usr/sbin directory. Note that it
         may be installed elsewhere on your system.


     B.  Install a new version of dip.
         If you need the functionality that dip provides, retrieve and install
         the following version of the source code for dip, which fixes this
         vulnerability. dip is available from

ftp://sunsite.unc.edu/pub/Linux/system/Network/serial/dip/dip337o-uri.tgz
ftp://sunsite.unc.edu/pub/Linux/system/Network/serial/dip/dip337o-uri.tgz.sig

         MD5   (dip337o-uri.tgz) = 45fc2a9abbcb3892648933cadf7ba090
         SHash (dip337o-uri.tgz) = 6e3848b9b5f9d5b308bbac104eaf858be4dc51dc


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The CERT Coordination Center staff thanks Uri Blumenthal for his solution to
the problem and Linux for their support in the development of 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).

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 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-96.13.dip_vul
           http://www.cert.org
               click on "CERT Advisories"


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Revision history

Aug. 30, 1996  Removed references to CA-96.13.README.




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