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CERT(r) Advisory CA-2000-03 Continuing Compromises of DNS servers

   Original release date: April 26, 2000
   Last revised: April 26, 2000
   Source: CERT/CC
Systems Affected

     * Systems running various vulnerable versions of BIND (including on
       machines where the system administrator does not realize a DNS
       server is running)

   This CERT Advisory addresses continuing compromises of machines
   running the Domain Name System (DNS) server software that is part of
   BIND ("named"), including compromises of machines that are not being
   used as DNS Servers. The Advisory also reports that a significant
   number of delegated(*) DNS servers in the tree are running
   outdated versions of DNS software, and urges system and network
   administrators to ensure that they are up-to-date with DNS security
   patches and workarounds.
   The CERT Coordination Center has received reports of continuing
   activity indicating that intruders are targeting machines running
   vulnerable versions of "named" . We continue to receive regular, daily
   reports that sites running unpatched, vulnerable versions of "named"
   have been compromised. CERT Advisory CA-99-14 "Multiple
   Vulnerabilities in BIND" describes the BIND NXT record privileged
   compromise vulnerability that is being exploited. We encourage you to
   review this advisory and to apply the appropriate patches if you have
   not done so already. The advisory is available at
   Some sites with compromised systems have found one of the following
   empty directories on systems where the NXT record vulnerability was
   successfully exploited:
   Other artifacts that are commonly found include
     * inetd started with an intruder-supplied configuration file in /tmp
       that provides a backdoor into the system
     * modified /etc/inittab and/or system startup files to load intruder
       processes at boot time
     * Trojan horse versions of sshd and /bin/login designed to provide a
       backdoor into a compromised system
     * complete rootkits that include Trojan horse replacements for
       system binaries, sniffers, denial-of-service tools, vulnerability
       scanners, exploits, etc.
     * newer versions of BIND
   Compromised systems are commonly used to search for and attack other
   potentially vulnerable systems.
   In many of the reports of DNS server compromises, compromised machines
   running DNS server software were not being used as DNS servers. The
   DNS server software was running because it was installed by default
   (unknowingly in many cases) when the machines were configured. This
   software was not up to date with security patches and workarounds; and
   since the system administrators were not planning to have the machines
   operate as DNS servers, they did not ensure the software was up to
   date, or simply disable the DNS server software on the machine. We
   encourage system and network administrators to disable DNS server
   software, and other services, on machines where the services are not
   We have also received information from Bill Manning of the USC/ISI
   concerning DNS servers running vulnerable versions of domain name
   server software. Since 1997, Bill Manning sweeps the inverse tree
   ( on a quarterly basis to verify the accuracy of
   delegations within that hierarchy. Using the first quarter survey
   results, he compiled a list of what version of DNS server software
   the servers were running. Of the responding DNS servers that are
   delegated(*) DNS servers for the zone, more than 50%
   of these DNS servers were running older, vulnerable versions of
   BIND (any vulnerabilities, not just the NXT vulnerability). This is
   significant because the compromise of DNS servers that are
   delegated DNS servers can have impact on the security of other
   organizations in addition to the organization operating the DNS
   A copy of the survey results are available at
   Based on the number of older versions being run, and the rate of
   compromises, we believe the number of DNS servers running older,
   vulnerable versions of BIND have not significantly decreased since the
   survey was published.
   We encourage DNS server operators to ensure that their DNS server
   software is up to date with the most recent versions of the DNS server
   software and that all security patches and workarounds have been
   delegated DNS server: a delegated DNS is a DNS server that is assigned
   responsibility for responding to requests for a portion of the DNS
   hierarchy. For more information on delegation, see the section on
   delegation in DNS and BIND third edition, by Paul Albitz and Cricket
   Liu, O'Reilly and Associates, 1998.
   Advisory Author: Jeffrey J. Carpenter
   The CERT Coordination Center thanks Bill Manning, USC/ISI, for
   providing information used in this CERT Advisory.
   This document is available from:
CERT/CC Contact Information

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          Phone: +1 412-268-7090 (24-hour hotline)
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          Postal address:
          CERT Coordination Center
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          Carnegie Mellon University
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