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The U.S. Department of Energy
Computer Incident Advisory Capability
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INFORMATION BULLETIN
dip Program Vulnerability
July 9, 1996 17:00 GMT Number G-29
______________________________________________________________________________
PROBLEM: A vulnerability in the dip program makes it possible to
overflow an internal buffer whose value is under the control of
the user of the dip program. The dip program manages the
connections needed for dial-up links such as SLIP and PPP.
PLATFORM: Linux systems for X86 hardware.
DAMAGE: On systems that have dip installed as set-user-id root, anyone
with access to an account on that system can gain root access.
SOLUTION: Disable the present installed version and install the new
version of dip.
______________________________________________________________________________
VULNERABILITY Exploitation scripts for dip have been found running on Linux
ASSESSMENT: systems for X86 hardware. However, exploitation scripts for
other architectures and operating systems have not been found,
but could be easily developed.
______________________________________________________________________________
[ Start of CERT Advisory ]
=============================================================================
CERT(sm) Advisory CA-96.13
July 9, 1996
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.
As we receive additional information relating to this advisory, we
will place it in
ftp://info.cert.org/pub/cert_advisories/CA-96.13.README
We encourage you to check our README files regularly for updates on
advisories 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
----------------------------------------------------------------------------
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.
----------------------------------------------------------------------------
[ End of CERT Advisory ]
_______________________________________________________________________________
CIAC wishes to acknowledge the contributions of CERT for the information
contained in this bulletin.
_______________________________________________________________________________
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