FW: CERT Advisory CA-2002-12 Format String Vulnerability in ISC D HCPD


Subject: FW: CERT Advisory CA-2002-12 Format String Vulnerability in ISC D HCPD
From: Leif Sawyer (lsawyer@gci.com)
Date: Wed May 08 2002 - 12:37:37 AKDT


Because so many of us use DHCPd ...

-----Original Message-----
From: CERT Advisory [mailto:cert-advisory@cert.org]
Sent: Wednesday, May 08, 2002 9:33 AM
To: cert-advisory@cert.org
Subject: CERT Advisory CA-2002-12 Format String Vulnerability in ISC
DHCPD

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CERT Advisory CA-2002-12 Format String Vulnerability in ISC DHCPD

   Original release date: May 8, 2002
   Last revised:--
   Source: CERT/CC

   A complete revision history can be found at the end of this file.

Systems Affected

     * ISC DHCPD 3.0 to 3.0.1rc8 inclusive

Overview

   The Internet Software Consortium (ISC) provides a Dynamic Host
   Configuration Protocol Daemon (DHCPD), which is a server that is used
   to allocate network addresses and assign configuration parameters to
   hosts. A format string vulnerability may permit a remote attacker to
   execute code with the privileges of the DHCPD (typically root). We
   have not seen active scanning or exploitation of this vulnerability.

I. Description

   ISC's DHCPD listens for requests from client machines connecting to
   the network. Versions 3 to 3.0.1rc8 (inclusive) of DHCPD contains an
   option (NSUPDATE) that is enabled by default. NSUPDATE allows the DHCP
   server to send information about the host to the DNS server after
   processing a DHCP request. The DNS server responds by sending an
   acknowledgement message back to the DHCP server that may contain
   user-supplied data (like a host name). When the DHCP server receives
   the acknowledgement message from the DNS server, it logs the
   transaction.

   A format string vulnerability exists in ISC's DHCPD code that logs the
   transaction. This vulnerability may permit a remote attacker to
   execute code with the privileges of the DHCP daemon.

II. Impact

   A remote attacker may be able to execute code with the privileges of
   the DHCPD (typically root).

III. Solution

   Note that some of the mitigation steps recommended below may have
   significant impact on your normal network operations. Ensure that any
   changes made based on the following recommendations will not
   unacceptably affect any of your operations.

Apply a patch from your vendor

   Appendix A contains information provided by vendors for this advisory.

Disable the DHCP service

   As a general rule, the CERT/CC recommends disabling any service or
   capability that is not explicitly required. Depending on your network
   configuration, you may not need to use DHCP.

Ingress filtering

   As a temporary measure, it may be possible to limit the scope of this
   vulnerability by blocking access to DHCP services at the network
   perimeter.

   Ingress filtering manages the flow of traffic as it enters a network
   under your administrative control. In the network usage policy of many
   sites, there are few reasons for external hosts to initiate inbound
   traffic to machines that provide no public services. Thus, ingress
   filtering should be performed at the border to prohibit externally
   initiated inbound traffic to non-authorized services. For DHCP,
   ingress filtering of the following ports can prevent attackers outside
   of your network from reaching vulnerable devices in the local network
   that are not explicitly authorized to provide public DHCP services.

   bootps 67/tcp # Bootstrap Protocol Server
   bootps 67/udp # Bootstrap Protocol Server
   bootpc 68/tcp # Bootstrap Protocol Client
   bootpc 68/udp # Bootstrap Protocol Client

Appendix A. - Vendor Information

   This appendix contains information provided by vendors for this
   advisory. As vendors report new information to the CERT/CC, we will
   update this section and note the changes in our revision history. If a
   particular vendor is not listed below, please check the Vulnerability
   Note (VU#854315) or contact your vendor directly.

Alcatel

     The security of our customers' networks is of highest priority for
     Alcatel. Alcatel is aware of this security issue in the DHCP
     implementation of ISC and has put measures in place to assess which
     of its products might be affected and to apply the necessary fixes
     where required. An update will be shortly published to provide more
     details on any affected products.

Conectiva

     Conectiva Linux 8 ships dhcp-3.0 and is vulnerable to this problem.
     Updates will be available at our ftp site and an announcement will
     be sent to our mailing lists as soon as CERT publishes its
     advisory.

F5 Networks, Inc.

     F5 Networks' products do not include any affected version of ISC's
     DHCPD, and are therefore not vulnerable.

FreeBSD

     The FreeBSD base system does not ship with the ISC dhcpd server by
     default and is not affected by this vulnerability. The ISC dhcpd
     server is available in the FreeBSD Ports Collection; updates to the
     ISC dhcp port (ports/net/isc-dhcp3) are in progress and corrected
     packages will be available in the near future.

IBM

     IBM's AIX operating system, all versions, is not vulnerable.

Internet Software Consortium

     A patch is included below, and we have a patched version of 3.0
     available (3.0pl1) and a new release candidate for the next bug-fix
     release (3.0.1RC9). Both of these new releases are not vulnerable.

     --- common/print.c Tue Apr 9 13:41:17 2002
     +++ common/print.c.patched Tue Apr 9 13:41:56 2002
     @@ -1366,8 +1366,8 @@
                    *s++ = '.';
            *s++ = 0;
            if (errorp)
     - log_error (obuf);
     + log_error ("%s",obuf);
            else
     - log_info (obuf);
     + log_info ("%s",obuf);
     }
     #endif /* NSUPDATE */
     
Lotus Development Corporation

     This issue does not affect Lotus products.

Microsoft Corporation

     Microsoft does not ship the ISC DHCPD program.

NetBSD

     NetBSD fixed this during a format string sweep performed on
     11-Oct-2000. No released version of NetBSD is vulnerable to this
     issue.

Silicon Graphics, Inc.

     SGI is not vulnerable.
     _________________________________________________________________

   The CERT Coordination Center acknowledges Next Generation Security
   Technologies as the discoverer of this vulnerability and thanks them
   and the Internet Software Consortium (ISC) for their cooperation,
   reporting, and analysis of this vulnerability.
     _________________________________________________________________

   Feedback can be directed to the author: Ian A. Finlay
   ______________________________________________________________________

   This document is available from:
   http://www.cert.org/advisories/CA-2002-12.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.

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   Copyright 2002 Carnegie Mellon University.

   Revision History
May 8, 2002: Initial release

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