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-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2000.216 -- FreeBSD-SA-00:34 dhclient vulnerable to malicious dhcp server 17 August 2000 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: dhclient Vendor: FreeBSD Operating System: FreeBSD 3.2 to 4.0 Linux Unix Platform: N/A Impact: Root Compromise Access Required: Remote Ref: ESB-2000.173 - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- ============================================================================= FreeBSD-SA-00:34 Security Advisory FreeBSD, Inc. Topic: dhclient vulnerable to malicious dhcp server Category: core, ports Module: dhclient, isc-dhcp2 (ports), isc-dhcp3 (ports) Announced: 2000-08-14 Affects: All releases of FreeBSD after FreeBSD 3.2-RELEASE and prior to the correction date (including FreeBSD 4.0 and 3.5, but not 4.1) Ports collection prior to the correction date. Credits: OpenBSD Vendor status: Updated version released Corrected: 2000-07-20 [FreeBSD 4.0 base system] 2000-08-01 [isc-dhcp2 port] 2000-07-21 [isc-dhcp3 port] FreeBSD only: NO I. Background ISC-DHCP is an implementation of the DHCP protocol containing client and server. FreeBSD 3.2 and above includes the version 2 client by default in the base system, and the version 2 and version 3 clients and servers in the Ports Collection. II. Problem Description The dhclient utility (DHCP client), versions 2.0pl2 and before (for the version 2.x series), and versions 3.0b1pl16 and before (for the version 3.x series) does not correctly validate input from the server, allowing a malicious DHCP server to execute arbitrary commands as root on the client. DHCP may be enabled if your system was initially configured from a DHCP server at install-time, or if you have specifically enabled it after installation. FreeBSD 4.1 is not affected by this problem since it contains the 2.0pl3 client. III. Impact An attacker who has or gains control of a DHCP server may gain additional root access to DHCP clients running vulnerable versions of ISC-DHCP. If you are not using dhclient to configure client machines via DHCP, or your DHCP server is "trusted" according to your local security policy, then this vulnerability does not apply to you. IV. Workaround Disable the use of DHCP for configuring client machines: remove the case-insensitive string "dhcp" from the "ifconfig_<foo>" directives in /etc/rc.conf and replace it with appropriate static interface configuration according to the rc.conf(5) manpage. An example of a DHCP-enabled interface is the following line in /etc/rc.conf: ifconfig_xl0="DHCP" V. Solution NOTE: At this time the FreeBSD 3.x branch has not yet been patched, due to logistical difficulties. Users running a vulnerable 3.x system are advised to either upgrade to FreeBSD 4.1, disable the use of DHCP as described above, or use the dhclient binary from the isc-dhcp2 port dated after the correction date. 1) Upgrade your vulnerable FreeBSD 4.0 system to a version dated after the correction date. See http://www.freebsd.org/handbook/makeworld.html for instructions on how to upgrade and recompile your FreeBSD system from source, or perform a binary upgrade, e.g. to FreeBSD 4.1-RELEASE, described here: http://www.freebsd.org/releases/4.1R/notes.html 2) (If using the isc-dhcp2 or isc-dhcp3 ports) One of the following: 2a) Upgrade your entire ports collection and rebuild the isc-dhcp2 or isc-dhcp3 port. 2b) Deinstall the old package and install a new package dated after the correction date, obtained from: [isc-dhcp3] ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/net/isc-dhcp3-3.0.b1.17.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/net/isc-dhcp3-3.0.b1.17.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/net/isc-dhcp3-3.0.b1.17.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/net/isc-dhcp3-3.0.b1.17.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/net/isc-dhcp3-3.0.b1.17.tgz NOTE: The isc-dhcp2 port is not available as a package. 2c) download a new port skeleton for the isc-dhcp2 or isc-dhcp3 port from: http://www.freebsd.org/ports/ and use it to rebuild the port. 2d) Use the portcheckout utility to automate option (3) above. The portcheckout port is available in /usr/ports/devel/portcheckout or the package can be obtained from: ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/portcheckout-2.0.tgz ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/portcheckout-2.0.tgz - -----BEGIN PGP SIGNATURE----- Version: 2.6.2 iQCVAwUBOZh3J1UuHi5z0oilAQHXBQQAmCLlTUfikHbgBelFd22agjTo/AVwR933 El0AMRHakiBJAHTMseZ4Nj+HyGUgVzD3oRMgmjx1u+HUCQM2/akuXXZdSHlur5Jc OyEGxcwxyzYXnNzWAL1vh6MYrpkGDfh74bHircLdO16d6uC1d+0VFmkxUOOFN4zb g7yK3m2ZOxo= =qTwd - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to use any or all of this information is the responsibility of each user or organisation, and should be done so in accordance with site policies and procedures. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the original authors to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/Information/advisories.html If you believe that your system has been compromised, contact AusCERT or your representative in FIRST (Forum of Incident Response and Security Teams). Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for emergencies. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBOaD0zyh9+71yA2DNAQGWCQQAmx7JGU9zyxgx8pWiFjfTEWWiwnazzXdd VVBDpELJf0GEjM9MHHuxpdtUPT3jPXbSmugGb0QHLpx/p6DMtCP7FIfs0EdpH+7l TAhVD0hWkYvVwQw3r7AHrtWxZhMp0NtJcW3qZ5QbMFudCFcnvIgGwOvVKwGgjwRc +rXl+vB5euA= =+XA3 -----END PGP SIGNATURE-----