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Text File | 1994-07-02 | 17KB | 393 lines

NASIRC BULLETIN #94-02 February 4, 1994 Network Monitoring Vulnerability and System Breakins =========================================================== __ __ __ ___ ___ ____ ____ /_/\ /_/| /_/ / _/\ /_/| / __/ \ / __/\ | |\ \| || / \ \ | /\/ | || | /\ \/ | | \/ | ||\ \ || / /\ \ \ \ \ | || |_\/ /\ | | | || \ \|| / /--\ \ \ /\_\\ | || | |\ \ \ | \_/\ |_|/ \_|//_/ \_\/ \/__/ |_|/ |_| \_\/ \___\/ NASA Automated Systems Incident Response Capability =========================================================== NASIRC has received the following information pertaining to network monitoring vulnerabilities associated with systems connected to the Internet or any private TCP/IP network. NASIRC will continue to monitor the situation and post additional information as it becomes available. The following guidelines have been extracted (with minor modifications) from the CERT Coordination Center's Advisory CA-94:01 and CIAC Advisory E-09, and full credit is given to them. [Beginning of modified CIAC extract.] NASIRC and other response teams affiliated with the Forum of Incident Response and Security Teams (FIRST) have observed many compromised systems surreptitiously monitoring network traffic, obtaining username, password, host-name combinations (and potentially other sensitive information) as users connect to remote systems using TELNET, RLOGIN, AND FTP. This is for both local and wide area network connections. The intruders may (and presumably do) use this information to compromise new hosts and expand the scope of their attacks. Once system administrators discover a compromised host, they must presume monitoring of all network transactions from or to any host "visible" on the network has taken place for the duration of the compromise, and that intruders potentially possess any of the information so exposed. The attacks proceed as follows: The intruders gain unauthorized, privileged access to a host that supports a network interface capable of monitoring the network in "promiscuous mode," reading every packet on the network whether addressed to the host or not. They accomplish this by exploiting unpatched vulnerabilities or learning a username, password, host-name combination from the monitoring log of another compromised host. The intruders then install a network monitoring tool that captures and records the initial portion of all network traffic for FTP, TELNET, AND RLOGIN sessions. They typically also install "Trojan" programs for LOGIN, PS, and TELNETD to support their unauthorized access and other clandestine activities. System administrators must begin by determining if intruders have compromised their systems. The CERT Coordination Center has released a tool to detect network interface devices in promiscuous mode. Instructions for obtaining and using the tool appears later in this bulletin--the tool is available via anonymous ftp. If a site discovers that intruders have compromised their systems, the site must determine the extent of the attack and perform recovery as described below. System administrators must also prevent future attacks as described below. NASIRC advises system administrators to follow the steps described below. The following guidelines have been extracted (with minor modifications) from the CERT Coordination Center's Advisory CA-94:01, and full credit is given to them. [End of modified CIAC extract.] [Beginning of CERT extract.] A. Detection The network monitoring tool can be run under a variety of process names and log to a variety of filenames. Thus, the best method for detecting the tool is to look for 1) Trojan horse programs commonly used in conjunction with this attack, 2) any suspect processes running on the system, and 3) the unauthorized use of /dev/nit. 1) Trojan horse programs: The intruders have been found to replace one or more of the following programs with a Trojan horse version in conjunction with this attack: /usr/etc/in.telnetd and /bin/login - Used to provide back-door access for the intruders to retrieve information /bin/ps - Used to disguise the network monitoring process Because the intruders install Trojan horse variations of standard UNIX commands, CERT recommends not using other commands such as the standard UNIX sum(1) or cmp(1) commands to locate the Trojan horse programs on the system until these programs can be restored from distribution media, run from read-only media (such as a mounted CD-ROM), or verified using cryptographic checksum information. In addition to the possibility of having the checksum programs replaced by the intruders, the Trojan horse programs mentioned above may have been engineered to produce the same standard checksum and timestamp as the legitimate version. Because of this, the standard UNIX sum(1) command and the timestamps associated with the programs are not sufficient to determine whether the programs have been replaced. CERT recommends that you use both the /usr/5bin/sum and /bin/sum commands to compare against the distribution media and assure that the programs have not been replaced. The use of cmp(1), MD5, Tripwire (only if the baseline checksums were created on a distribution system), and other cryptographic checksum tools are also sufficient to detect these Trojan horse programs, provided these programs were not available for modification by the intruder. If the distribution is available on CD-ROM or other read-only device, it may be possible to compare against these volumes or run programs off these media. 2) Suspect processes: Although the name of the network monitoring tool can vary from attack to attack, it is possible to detect a suspect process running as root using ps(1) or other process-listing commands. Until the ps(1) command has been verified against distribution media, it should not be relied upon--a Trojan horse version is being used by the intruders to hide the monitoring process. Some process names that have been observed are sendmail, es, and in.netd. The arguments to the process also provide an indication of where the log file is located. If the "-F" flag is set on the process, the filename following indicates the location of the log file used for the collection of authentication information for later retrieval by the intruders. If the network monitoring tool is currently running on your system, it is possible to detect this by checking for unauthorized use of the /dev/nit interface. CERT has created a minimal tool for this purpose. The source code for this tool is available via anonymous FTP on nasirc.nasa.gov in the /toolkits/UNIX/cpm directory as cpm.1.0.tar.Z. The checksum information is: Filename Standard UNIX Sum System V Sum -------------- ----------------- ------------ cpm.1.0.tar.Z: 11097 6 24453 12 MD5 Checksum MD5 (cpm.1.0.tar.Z) = e29d43f3a86e647f7ff2aa453329a155 This archive contains a readme file, also included at the end of this extract, containing instructions on installing and using this detection tool. B. Prevention There are two actions that are effective in preventing this attack. A long-term solution requires eliminating transmission of clear-text passwords on the network. For this specific attack, however, a short-term workaround exists. Both of these are described below. 1) Long-term prevention: CERT recognizes that the only effective long-term solution to prevent these attacks is by not transmitting reusable clear-text passwords on the network. CERT has collected some information on relevant technologies. This information is included as Appendix B in this advisory. Note: These solutions will not protect against transient or remote access transmission of clear-text passwords through the network. Until everyone connected to your network is using the above technologies, your policy should allow only authorized users and programs access to promiscuous network interfaces. The tool described in Section III.A.3 above may be helpful in verifying this restricted access. 2) Short-term workaround: Regardless of whether the network monitoring software is detected on your system, CERT recommends that ALL SITES take action to prevent unauthorized network monitoring on their systems. You can do this either by removing the interface, if it is not used on the system or by attempting to prevent the misuse of this interface. For systems other than Sun and Solbourne, contact your vendor to find out if promiscuous mode network access is supported and, if so, what is the recommended method to disable or monitor this feature. For SunOS 4.x and Solbourne systems, the promiscuous interface to the network can be eliminated by removing the /dev/nit capability from the kernel. The procedure for doing so is outlined below (see your system manuals for more details). Once the procedure is complete, you may remove the device file /dev/nit since it is no longer functional. Procedure for removing /dev/nit from the kernel: 1. Become root on the system. 2. Apply "method 1" as outlined in the System and Network Administration manual, in the section, "Sun System Administration Procedures," Chapter 9, "Reconfiguring the System Kernel." Excerpts from the method are reproduced below: # cd /usr/kvm/sys/sun[3,3x,4,4c]/conf # cp CONFIG_FILE SYS_NAME [Note that at this step, you should replace the CONFIG_FILE with your system specific configuration file if one exists.] # chmod +w SYS_NAME # vi SYS_NAME # # The following are for streams NIT support. NIT is used by # etherfind, traffic, rarpd, and ndbootd. As a rule of thumb, # NIT is almost always needed on a server and almost never # needed on a diskless client. # pseudo-device snit # streams NIT pseudo-device pf # packet filter pseudo-device nbuf # NIT buffering module [Comment out the preceding three lines; save and exit the editor before proceeding.] # config SYS_NAME # cd ../SYS_NAME # make # mv /vmunix /vmunix.old # cp vmunix /vmunix # /etc/halt > b [This step will reboot the system with the new kernel.] [NOTE that even after the new kernel is installed, you need to take care to ensure that the previous vmunix.old , or other kernel, is not used to reboot the system.] C. Scope and recovery If you detect the network monitoring software at your site, CERT recommends following three steps to successfully determine the scope of the problem and to recover from this attack. 1. Restore the system that was subjected to the network monitoring software. The systems on which the network monitoring and/or Trojan horse programs are found have been compromised at the root level; your system configuration may have been altered. See Appendix A of this advisory for help with recovery. 2. Consider changing router, server, and privileged account passwords due to the wide-spread nature of these attacks. Since this threat involves monitoring remote connections, take care to change these passwords using some mechanism other than remote telnet, rlogin, or FTP access. 3. Urge users to change passwords on local and remote accounts. Users who access accounts using telnet, rlogin, or FTP either to or from systems within the compromised domain should change their passwords after the intruder's network monitor has been disabled. 4. Notify remote sites connected from or through the local domain of the network compromise. Encourage the remote sites to check their systems for unauthorized activity. Be aware that if your site routes network traffic between external domains, both of these domains may have been compromised by the network monitoring software. --------------------------------------------------------------------------- cpm 1.0 README FILE cpm - check for network interfaces in promiscuous mode. Copyright (c) Carnegie Mellon University 1994 Thursday Feb 3 1994 CERT Coordination Center Software Engineering Institute Carnegie Mellon University Pittsburgh, PA 15213-3890 This program is free software; you can distribute it and/or modify it as long as you retain the Carnegie Mellon copyright statement. It can be obtained via anonymous FTP from nasirc.nasa.gov in directory ~ftp/toolkits/UNIX/cpm/cpm.1.0.tar.Z. This program is distributed WITHOUT ANY WARRANTY; without the IMPLIED WARRANTY of merchantability or fitness for a particular purpose. This package contains: README MANIFEST cpm.1 cpm.c To create cpm under SunOS, type: % cc -Bstatic -o cpm cpm.c On machines that support dynamic loading, such as Sun's, CERT recommends that programs be statically linked so that this feature is disabled. CERT recommends that after you install cpm in your favorite directory, you take measures to ensure the integrity of the program by noting the size and checksums of the source code and resulting binary. The following is an example of the output of cpm and its exit status. Running cpm on a machine where both the le0 and le2 interfaces are in promiscuous mode, under csh(1): % cpm le0 le2 % echo $status 2 % Running cpm on a machine where no interfaces are in promiscuous mode, under csh(1): % cpm % echo $status 0 % [End of CERT extract.] =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= NASIRC ACKNOWLEDGES: ARPA/CERT and DoE CIAC for their reporting and coordination of solutions to this problem =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= The NASIRC online archive system is available via anonymous ftp. Just ftp to nasirc.nasa.gov and login as anonymous. You will be required to enter your valid e-mail address. Once there you can access the following information: /toolkits ! contains automated toolkit software /bulletins ! contains NASIRC bulletins Information maintained in these directories will be updated on a continuous basis with relevant software and information. Contact the NASIRC Helpdesk for more information and assistance with toolkits or security measures. =============================================================== For further assistance, please contact the NASIRC Helpdesk: Phone: 1-800-7-NASIRC Fax: 1-301-441-1853 Internet Email: nasirc@nasa.gov 24 Hour/Emergency Pager: 1-800-759-7243/Pin:2023056 STU III: 1-301-982-5480 =============================================================== This bulletin may be forwarded without restrictions to sites and system administrators within the NASA community ----------------- PLEASE NOTE: Users outside of the NASA community may receive NASIRC bulletins. If you are not part of the NASA community, please contact your agency's response team to report incidents. Your agency's team will coordinate with NASIRC, who will ensure the proper internal NASA team(s) are notified. NASIRC is a member of the Forum of Incident Response and Security Teams (FIRST), a world-wide organization which provides for coordination between incident response teams in handling computer-security-related issues. A list of FIRST member organizations and their constituencies can be obtained by sending email to docserver@first.org with an empty subject line and a message body containing the line: send first-contacts.