-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= 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 - --------------------------------------------------------------------------- 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. - --------------------------------------------------------------------------- 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. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBMiTEbHVP+x0t4w7BAQE9CAQAvUU6roTvYG+pMzUiAsSKOKkzSCBgVFHr 3n90176UxogW8MDKjBoX7z3R3VXoAe2AG0zArQ5Kd4l0hYNqc7V/1LqxpaaiCL7o epz9xp402IofSLhkCuThjzgEJjJYEihJtFNLoy1SyYEk4j5c16PIey6RcEM+Izsc 30mQPwwP+Do= =VsOI -----END PGP SIGNATURE-----