-----BEGIN PGP SIGNED MESSAGE----- CERT Advisory CA-2001-21 Buffer Overflow in telnetd Original release date: July 24, 2001 Last revised: -- Source: CERT/CC A complete revision history can be found at the end of this file. Systems Affected Systems running versions of telnetd derived from BSD source. Overview The telnetd program is a server for the Telnet remote virtual terminal protocol. There is a remotely exploitable buffer overflow in Telnet daemons derived from BSD source code. This vulnerability can crash the server, or be leveraged to gain root access. I. Description There is a remotely exploitable buffer overflow in Telnet daemons derived from BSD source code. During the processing of the Telnet protocol options, the results of the "telrcv" function are stored in a fixed-size buffer. It is assumed that the results are smaller than the buffer and no bounds checking is performed. The vulnerability was discovered by TESO. An exploit for this vulnerability has been publicly released; internal testing at CERT/CC confirms this exploit works against at least one target system. For more information, see http://www.team-teso.net/advisories/teso-advisory-011.tar.gz II. Impact An intruder can execute arbitrary code with the privileges of the telnetd process, typically root. III. Solution Apply a patch Appendix A contains information from vendors who have provided information for this advisory. We will update the appendix as we receive more information. If you do not see your vendor's name, the CERT/CC did not hear from that vendor. Please contact your vendor directly. Restrict access to the Telnet service (typically port 23/tcp) using a firewall or packet-filtering technology. Until a patch can be applied, you may wish to block access to the Telnet service from outside your network perimeter. This will limit your exposure to attacks. However, blocking port 23/tcp at a network perimeter would still allow attackers within the perimeter of your network to exploit the vulnerability. It is important to understand your network's configuration and service requirements before deciding what changes are appropriate. Appendix A. - Vendor Information This appendix contains information provided by vendors for this advisory. When vendors report new information to the CERT/CC, we update this section and note the changes in our revision history. If a particular vendor is not listed below, we have not received their comments. BSDI All current versions of BSD/OS are vulnerable. Patches are available via our web site at http://www.bsdi.com/services/support/patches and via ftp at ftp://ftp.bsdi.com/bsdi/support/patches as soon as testing has been completed. Cisco Systems Cisco IOS does not appear to be vulnerable. Certain non-IOS products are supplied on other operating system platforms which themselves may be vulnerable as described elsewhere in this CERT Advisory. The Cisco PSIRT is continuing to investigate the vulnerability to be certain and, if necessary, will provide updates to the CERT and publish an advisory. Cisco Security Advisories are on-line at http://www.cisco.com/go/psirt/. FreeBSD All released versions of FreeBSD are vulnerable to this problem, which was fixed in FreeBSD 4.3-STABLE and FreeBSD 3.5.1-STABLE on July 23, 2001. An advisory has been released, along with a patch to correct the vulnerability and a binary upgrade package suitable for use on FreeBSD 4.3-RELEASE systems. For more information, see the advisory at the following location: ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-01:49.telnetd.asc or use an FTP mirror site from the following URL: http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/mirrors-ftp.html Hewlett-Packard [This issue is] actively under investigation to determine vulnerability ramifications. Sun Microsystems Sun is currently investigating and have confirmed that one can make the in.telnetd daemon dump core but Sun has not yet determined if this issue is potentially exploitable on Solaris. Appendix B. - References 1. http://www.ietf.org/rfc/rfc0854.txt 2. http://www.team-teso.net/advisories/teso-advisory-011.tar.gz 3. http://www.kb.cert.org/vuls/id/745371 4. ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-01:49.telnetd.asc _________________________________________________________________ _________________________________________________________________ The CERT Coordination Center thanks TESO, who published an advisory on this issue. We would also like to thank Jeff Polk for technical assistance. _________________________________________________________________ Authors: Jason A. Rafail, Ian A. Finlay, and Shawn V. Hernan. ______________________________________________________________________ This document is available from: http://www.cert.org/advisories/CA-2001-21.html ______________________________________________________________________ CERT/CC Contact Information Email: cert@cert.org Phone: +1 412-268-7090 (24-hour hotline) Fax: +1 412-268-6989 Postal address: CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh PA 15213-3890 U.S.A. CERT personnel answer the hotline 08:00-17:00 EST(GMT-5) / EDT(GMT-4) Monday through Friday; they are on call for emergencies during other hours, on U.S. holidays, and on weekends. Using encryption We strongly urge you to encrypt sensitive information sent by email. Our public PGP key is available from http://www.cert.org/CERT_PGP.key If you prefer to use DES, please call the CERT hotline for more information. Getting security information CERT publications and other security information are available from our web site http://www.cert.org/ To subscribe to the CERT mailing list for advisories and bulletins, send email to majordomo@cert.org. Please include in the body of your message subscribe cert-advisory * "CERT" and "CERT Coordination Center" are registered in the U.S. Patent and Trademark Office. ______________________________________________________________________ NO WARRANTY Any material furnished by Carnegie Mellon University and the Software Engineering Institute is furnished on an "as is" basis. Carnegie Mellon University makes no warranties of any kind, either expressed or implied as to any matter including, but not limited to, warranty of fitness for a particular purpose or merchantability, exclusivity or results obtained from use of the material. Carnegie Mellon University does not make any warranty of any kind with respect to freedom from patent, trademark, or copyright infringement. _________________________________________________________________ Conditions for use, disclaimers, and sponsorship information Copyright 2001 Carnegie Mellon University. Revision History July 24, 2001: Initial release -----BEGIN PGP SIGNATURE----- Version: PGPfreeware 5.0i for non-commercial use Charset: noconv iQCVAwUBO14kUgYcfu8gsZJZAQHsZAP/V+d+lCvTxW2z4tCWoFTYri/cwuVtKJbg 7tP11jlPMQjYraTLpF2dEwFedikk31PRCBWsTHksfw7tV5ntsz58avZ+4K4NZeJj bEBTegtRHTRgwDQMv6AApz8tNVpAVhk4TBxKYoQENK0t1nwwO/Cluywy7mPWDXZY 6Jb+p+9Ai78= =Eu3D -----END PGP SIGNATURE-----