-----BEGIN PGP SIGNED MESSAGE----- - -----BEGIN PGP SIGNED MESSAGE----- __________________________________________________________ The U.S. Department of Energy Computer Incident Advisory Capability ___ __ __ _ ___ / | /_\ / \___ __|__ / \ \___ __________________________________________________________ INFORMATION BULLETIN E-Mail Spamming countermeasures Detection and prevention of E-Mail spamming October 20, 1997 19:00 GMT Number I-005a _____________________________________________________________________________ PROBLEM: Unsolicited E-Mail. PLATFORM: All platforms which accept E-Mail from the Internet DAMAGE: Loss of user productivity and reduction of availability of resources. SOLUTION: Follow the guidelines outlined below. _____________________________________________________________________________ VULNERABILITY Programs which implement this type of malicious activity ASSESSMENT: are in widespread use. No legal remedies are available yet. _____________________________________________________________________________ INTRODUCTION: Spam (aka UCE: Unsolicited Commercial E-Mail) is the Internet version of "Junk E-Mail." It is an attempt to deliver a message, over the Internet, to someone who would not otherwise choose to receive it. Almost all spam is commercial advertising. Potential target lists are created by scanning Usenet postings, stealing Internet mailing lists, or searching the Web for addresses. Such information is gathered with automated searches to retrieve E-Mail addresses for spamming. The low cost of E-Mail spamming engines offered for sale with millions of E-Mail addresses, coupled with the fact that the sender does not pay extra to send E-Mail, has resulted in the current explosive growth of "junk E-Mail." Currently, unless the spammer offers to sell illegal items, there is no legal remedy to use to stop E-Mail spammers. Congress is currently considering legislation to require the marking of unsolicited commercial E-Mail (UCE), but that legislation is not yet complete. TERMINOLOGY: Mail User Agent (MUA). This refers to the program used by the client to send and receive E-Mail from. It is usually referred to as the "mail client." An example of this is pine or eudora. Mail Transfer Agent (MTA). This refers to the program used running on the server to store and forward E-Mail messages. It is usually referred to as the "mail server program." An example of this is sendmail or the server part of exchange. CONFIGURATION AND USAGE GUIDELINES: Mail filtering in the MTA or MDA is the only practical solution today and it is less than perfect. There are three primary information sources used to filter incoming E-Mail : - Header Information - Mailer Type (a special type of Header information) - IP Address (domain name). Header filtering is performed by scanning the header and/or envelope of a message, and comparing that information to a list of "filters." If the "From", "X-Sender", or "Sender" address is in the "filtering" list, the message is dropped. Filtering by E-Mail envelope and/or header information on the MDA or MTA is the most effective way of limiting spam on your network. Filtering on the MTA is accomplished by adding rules to the configuration for the specific mail system running on the server. The MDA filtering is accomp- lished through configuration rules in the client uses to read mail. The most logical location for filtering is your MTA, since it can perform this service for a larger number of mail accounts and is a central point for administra- tion. The down side to this is that users need to feedback "SPAM" informa- tion to the E-Mail administrators to be incorporated into an organization- wide filtering list. This requires continuous maintenance to keep the spamming filters list up-to-date, since it is built in reaction to spamming activity. Predetermined "filtering" lists are available in the public domain. Also, if the spamming filter list is not made with care, valid E-Mail messages may be discarded along with the spam. Mailer filtering uses the specific Header information field: "X-mailer." This type of filtering enables you to eliminate an entire class of senders -- those who use suspect Mail Delivery Agents. Some of the more popular MDA's with spammers are: Pegasus, Floodgate, Extractor, Fusion, MassE-Mail, Quick Shot, NetMailer, and WorldMerge. Be aware that, as with other Header filtering, filtering on "X-mailer" always runs the risk of eliminating legitimate E-Mail from people using these mailers. It is the person and not the mailer that is the problem. Lastly, you can filter traffic from a domain or range of IP addresses. This is probably the easiest way to limit spam from those addresses associated with spamming. Again you may also block mail from legitimate users. SOME DO NOTS Do NOT spam, mail bomb, or hack spammers. In many cases the site indicated as the source of the spamming is not the spammers real site, so attacking that site is not only wrong, but you are actually "spamming" yourself. DO NOT Sending "remove" messages to a spammer. It simply validates your E-Mail address for future spammings. DO NOT act as a gateways for spammers. Use an MTA that will facilitate blocking the forwarding of messages by spammers off of your organizations SMTP ports. Currently sendmail has filters to prevent this. MTA's that do not have this capability can be protected by rerouting all mail for the domain through a host running sendmail with filters. The sendmail server then hands the messages to the preferred mail server which is hidden by router filters. Site E-Mail administrators should work closely with their users to make the list decision about sites, mailers, and senders to be blocked. There should be a role address (abuse@someorg.gov, spam@someorg.gov) to which complaints can be sent. Pointers on the actual implementation of filtering methodologies: Filtering mail to your personal account http://spam.abuse.net/spam/tools/mailblock.html#filters Blocking spam E-Mail for an entire site http://spam.abuse.net/spam/tools/mailblock.html Blocking IP connectivity from spam sites http://spam.abuse.net/spam/tools/ipblock.html Sendmail Information http://www.sendmail.org/antispam.html _____________________________________________________________________________ CIAC wishes to acknowledge the contributions of Shawn Hernan, James R. Cutler, Dax Kelson, and Eric Frisch for the information contained in this bulletin. _____________________________________________________________________________ CIAC, the Computer Incident Advisory Capability, is the computer security incident response team for the U.S. Department of Energy (DOE) and the emergency backup response team for the National Institutes of Health (NIH). CIAC is located at the Lawrence Livermore National Laboratory in Livermore, California. CIAC is also a founding member of FIRST, the Forum of Incident Response and Security Teams, a global organization established to foster cooperation and coordination among computer security teams worldwide. CIAC services are available to DOE, DOE contractors, and the NIH. CIAC can be contacted at: Voice: +1 510-422-8193 FAX: +1 510-423-8002 STU-III: +1 510-423-2604 E-Mail: ciac@llnl.gov For emergencies and off-hour assistance, DOE, DOE contractor sites, and the NIH may contact CIAC 24-hours a day. During off hours (5PM - 8AM PST), call the CIAC voice number 510-422-8193 and leave a message, or call 800-759-7243 (800-SKY-PAGE) to send a Sky Page. CIAC has two Sky Page PIN numbers, the primary PIN number, 8550070, is for the CIAC duty person, and the secondary PIN number, 8550074 is for the CIAC Project Leader. Previous CIAC notices, anti-virus software, and other information are available from the CIAC Computer Security Archive. World Wide Web: http://ciac.llnl.gov/ Anonymous FTP: ciac.llnl.gov (198.128.39.53) Modem access: +1 (510) 423-4753 (28.8K baud) +1 (510) 423-3331 (28.8K baud) CIAC has several self-subscribing mailing lists for electronic publications: 1. CIAC-BULLETIN for Advisories, highest priority - time critical information and Bulletins, important computer security information; 2. SPI-ANNOUNCE for official news about Security Profile Inspector (SPI) software updates, new features, distribution and availability; 3. SPI-NOTES, for discussion of problems and solutions regarding the use of SPI products. Our mailing lists are managed by a public domain software package called Majordomo, which ignores E-Mail header subject lines. To subscribe (add yourself) to one of our mailing lists, send the following request as the E-Mail message body, substituting ciac-bulletin, spi-announce OR spi-notes for list-name: E-Mail to ciac-listproc@llnl.gov or majordomo@tholia.llnl.gov: subscribe list-name e.g., subscribe ciac-bulletin You will receive an acknowledgment E-Mail immediately with a confirmation that you will need to mail back to the addresses above, as per the instructions in the E-Mail. This is a partial protection to make sure you are really the one who asked to be signed up for the list in question. If you include the word 'help' in the body of an E-Mail to the above address, it will also send back an information file on how to subscribe/unsubscribe, get past issues of CIAC bulletins via E-Mail, etc. PLEASE NOTE: Many users outside of the DOE, ESnet, and NIH computing communities receive CIAC bulletins. If you are not part of these communities, please contact your agency's response team to report incidents. Your agency's team will coordinate with CIAC. The Forum of Incident Response and Security Teams (FIRST) is a world-wide organization. A list of FIRST member organizations and their constituencies can be obtained via WWW at http://www.first.org/. This document was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor the University of California nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial products, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation or favoring by the United States Government or the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or the University of California, and shall not be used for advertising or product endorsement purposes. LAST 10 CIAC BULLETINS ISSUED (Previous bulletins available from CIAC) H-105: HP-UX vuefile, vuepad, dtfile, & dtpad Vulnerabilities H-106: SGI IRIX LOCKOUT & login/scheme Vulnerabilities H-107: UNIX Buffer Overflow in rdist Vulnerability H-108: SunOS, Solaris libX11 Buffer Overflow Vulnerability H-109: Solaris DCE and AFS Integrated login Vulnerability H-110: Samba Servers Vulnerability I-001: HP-UX Denial of Service via telnet Vulnerability I-002: Cisco CHAP Authentication Vulnerability I-003: HP-UX mediainit(1) Vulnerability I-004: NEC/UNIX "nosuid" mount option Vulnerability - -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAgUBNFEJHrnzJzdsy3QZAQFEYgP+LomEezD7/5rwUGppRLzpkHK/89woE7Ge MCyef5dxOljutIhSAT+IvZFKD9Is61aJ1HjBIar2t7Wo+80EqHNjYM9JhyBZN2lF 7EhJwxWxJ3G7YHXPJ8AwQt+R5CB4E0RwtKZyWBfFPk+m+NXTnor88Y9uJll6vo8M 0J4rXmsCFXo= =kpry - -----END PGP SIGNATURE----- -----BEGIN PGP SIGNATURE----- Version: 4.0 Business Edition iQCVAwUBNFEPqbnzJzdsy3QZAQF2KAP9GCNEjqXDPp7H3eob2lIxOdiC7upy5U0E fXWTyNCLIkufpk+7I6FFjshOTgKeVV8iIoHc8en0i7mL/wCXw7ZvQkPiPjpZKCLJ N4MBIVOdEIHoDj2LLGf1t6Q7CCJnX0TVCtcHWn/86KWP5tzpUzibQOeoalROrNym 8GNOBEdGf/E= =xqKS -----END PGP SIGNATURE-----