-----BEGIN PGP SIGNED MESSAGE----- ============================================================================= CERT* Advisory CA-97.28 Original issue date: Dec. 16, 1997 Last revised: December 17, 1997 - Added or updated vendor information for Caldera, NCR, BSDI, and Sun. A complete revision history is at the end of this file. Topic: IP Denial-of-Service Attacks - ----------------------------------------------------------------------------- The CERT Coordination Center has received reports of two attack tools (Teardrop and Land) that are being used to exploit two vulnerabilities in the TCP/IP protocol. Both tools enable a remote user to cause a denial of service. The CERT/CC team recommends installing patches from your vendor. Until you are able to do so, we urge you to use the workaround described in Section III.B. to reduce the likelihood of a successful attack using Land. There is no workaround for Teardrop. We will update this advisory as we receive additional information. Please check our advisory files regularly for updates that relate to your site. - ----------------------------------------------------------------------------- I. Description In recent weeks there has been discussion on public mailing lists about two denial-of-service attack tools, Teardrop and Land. These attack tools have similar effects on some systems (namely, causing the victim machine to crash), but the tools exploit different vulnerabilities. The CERT Coordination Center has received several reports of sites being attacked by either one or both of these tools. It is important to note that it may be necessary for a system administrator to apply separate patches, if they exist, for each attack tool. Topic 1 - Teardrop Some implementations of the TCP/IP IP fragmentation re-assembly code do not properly handle overlapping IP fragments. Teardrop is a widely available attack tool that exploits this vulnerability. Topic 2 - Land Some implementations of TCP/IP are vulnerable to packets that are crafted in a particular way (a SYN packet in which the source address and port are the same as the destination--i.e., spoofed). Land is a widely available attack tool that exploits this vulnerability. II. Impact Topic 1 - Teardrop Any remote user can crash a vulnerable machine. Topic 2 - Land Any remote user that can send spoofed packets to a host can crash or "hang" that host. III. Solution CERT/CC urges you to immediately apply vendor patches if they are available. You may have to apply different patches for each attack tool. You may want to use the workaround for Land, so please review both Sections A and B below. A. Consult your vendor Appendix A contains information from vendors who provided input 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. It is important to note that you may have to apply different patches for each attack tool. B. Apply the following workaround (Land only) A workaround for the Land attack tool is to block IP-spoofed packets. This workaround does not apply to the Teardrop attack tool because the Teardrop attack does not rely on IP-spoofed packets. Attacks like those of the Land tool rely on the use of forged packets, that is, packets where the attacker deliberately falsifies the origin address. With the current IP protocol technology, it is impossible to eliminate IP-spoofed packets. However, you can reduce the likelihood of your site's networks being used to initiate forged packets by filtering outgoing packets that have a source address different from that of your internal network. Currently, the best method to reduce the number of IP-spoofed packets exiting your network is to install filtering on your routers that requires packets leaving your network to have a source address from your internal network. This type of filter prevents a source IP spoofing attack from your site by filtering all outgoing packets that contain a source address from a different network. A detailed description of this type of filtering is available in the Internet Draft "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing" by Paul Ferguson of Cisco Systems, Inc. and Daniel Senie of Blazenet, Inc. Note that although this document is labeled as an IETF "working draft," the content is complete and it is being proposed as an Informational RFC. We recommend it to both Internet Service Providers and sites that manage their own routers. The document is currently available at http://ds.internic.net/internet-drafts/draft-ferguson-ingress-filtering-03.txt ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Appendix A - Vendor Information Below is a list of the vendors who have provided information for this advisory. We will update this appendix as we receive additional information. If you do not see your vendor's name, the CERT/CC did not hear from that vendor. Please contact the vendor directly. Berkeley Software Design, Inc. (BSDI) ===================================== No version of BSD/OS is vulnerable to Teardrop. Patched versions of 2.1 and all 3.0 and 3.1 versions are also not vulnerable to Land. Caldera Corporation =================== Topic 1 - Teardrop Unless patched, Linux 2.0.x kernels prior to 2.0.32 are vulnerable. With the application of the kernel update described in Caldera Security Advisory SA-1997.29 (dated 3-Dec-1997), Caldera OpenLinux is not vulnerable. This Caldera advisory describes how to obtain and install the update and can be found at: http://www.caldera.com/tech-ref/security/SA-1997.29.html Other Caldera Security Advisories can be found at: http://www.caldera.com/tech-ref/security/ Topic 2 - Land There are no known reports of any version of the Linux kernel, including those shipping with Caldera OpenLinux, being vulnerable to this exploit. Cisco Systems ============= Topic 1 - Teardrop No feedback. Topic 2 - Land IOS/7000 software, Catalyst 5xxx and 29xx LAN switches, BPX and IGX WAN switches and AXIS shelf appear to be vulnerable. PIX firewall and Centri firewall are not vulnerable. For more information reference URL: http://www.cisco.com/warp/public/770/land-pub.shtml Digital Equipment Corporation ============================= This reported problem is not present for Digital's ULTRIX or Digital UNIX Operating Systems Software. The FreeBSD Project =================== Topic 1 - Teardrop CSRG 4.4 is not vulnerable. Topic 2 - Land No feedback. Hewlett-Packard Corporation =========================== HP is vulnerable, patches in process. Watch for HP Security Bulletin to be issued. IBM Corporation =============== Topic 1 - Teardrop AIX is not vulnerable. Topic 2 - Land AIX is not vulnerable. Microsoft Corporation ===================== Topic 1 - Teardrop Windows NT 4.0 with SP 3 and post SP 3 fixes applied and Windows 95 with the appropriate patch are not vulnerable. Patch information is available at URL: ftp://ftp.microsoft.com/bussys/winnt/kb/Q154/1/74.TXT Topic 2 - Land Windows NT 4.0 with the appropriate patch is not vulnerable. Patch information is available at URL: ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/ hotfixes-postSP3/land-fix/Q165005.txt Windows 95 without the WinSock 2.0 Update is not vulnerable. Patch information is available at URL: ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/nt40/ hotfixes-postSP3/land-fix/Q177539.TXT NCR Corporation =============== Topic 1 - Teardrop NCR MP-RAS TCP/IP implementation is not vulnerable. Topic 2 - Land Apply a patch for your MP-RAS UNIX TCP/IP depending on the revision of the inet package installed on your system. To check its version execute: pkginfo -x inet For inet 5.01.xx.xx: - PINET501 (Version later than 05.01.01.08) For inet 6.01.xx.xx. - Not vulnerable. For inet 6.02.xx.xx. - Not vulnerable. The NetBSD Project ================== Topic 1 - Teardrop Versions 1.2 and above are not vulnerable. Topic 2 - Land No feedback. Red Hat Software ================ Topic 1 - Teardrop Linux is not vulnerable. Topic 2 - Land Linux is not vulnerable. Sun Microsystems, Inc. ====================== Topic 1 - Teardrop All releases of Solaris are not vulnerable. All supported versions of SunOS 4.1.x (4.1.3_U1 and 4.1.4) are not vulnerable. Topic 2 - Land All releases of Solaris are not vulnerable. SunOS 4.1.3_U1 and 4.1.4 are vulnerable and patches are in progress. - --------------------------------------------------------------------------- The CERT Coordination Center thanks Paul Ferguson and Daniel Senie for providing information on network ingress filtering. - ---------------------------------------------------------------------------- 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 (see http://www.first.org/team-info/). CERT/CC 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 Using encryption We strongly urge you to encrypt sensitive information sent by email. We can support a shared DES key or PGP. Contact the CERT/CC for more information. Location of CERT PGP key ftp://ftp.cert.org/pub/CERT_PGP.key Getting security information CERT publications and other security information are available from http://www.cert.org/ ftp://ftp.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 advisories and bulletins, send email to cert-advisory-request@cert.org In the subject line, type SUBSCRIBE your-email-address - --------------------------------------------------------------------------- Copyright 1997 Carnegie Mellon University. Conditions for use, disclaimers, and sponsorship information can be found in http://www.cert.org/legal_stuff.html and ftp://ftp.cert.org/pub/legal_stuff . If you do not have FTP or web access, send mail to cert@cert.org with "copyright" in the subject line. *CERT is registered in the U.S. Patent and Trademark Office. - --------------------------------------------------------------------------- This file: ftp://ftp.cert.org/pub/cert_advisories/CA-97.28.Teardrop_Land http://www.cert.org click on "CERT Advisories" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Revision history Dec. 17, 1997 Added or updated vendor information for Caldera, NCR, BSDI, and Sun. Dec. 16, 1997 Added vendor information for Digital Equipment Corporation and Hewlett-Packard. -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBNJqbZXVP+x0t4w7BAQFw1gP/a1k4yDO7n4avxiaH3DkxHT2reC55uC8a h+Z3qftD/EycwSXclzMZJnGcjlz22K2YCK1wwjl53KR4HwQSUv8IJuwu8scMVDhL Z59EPzqAXEQZOKjic7rtLZwembSWakgLgwYPuT/3jMdmPzFZmatUw4zWVEgtRaIO v+cUHc9Somo= =Q276 -----END PGP SIGNATURE-----