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Transcript of © Copyright 2003 – Chesapeake NetCraftsmen, LLC SPAM Joe Roundy Senior Security Consultant...
© Copyright 2003 – Chesapeake NetCraftsmen, LLC
SPAM
Joe Roundy
Senior Security Consultant
© Copyright 2005– Chesapeake NetCraftsmen
About the Presenter
Joe RoundySenior Security ConsultantChesapeake NetCraftsmen, LLCCISSP #4848jroundy@netcraftsmen,net
© Copyright 2005– Chesapeake NetCraftsmen
Agenda
Introduction to SPAM Stopping Spam Tracking, Blocking, and Filtering Spam Spam Filtering Architectures and
Examples
© Copyright 2003 – Chesapeake NetCraftsmen, LLC
Introduction to SPAM
© Copyright 2005– Chesapeake NetCraftsmen
What is SPAM
Hawaii residents consume nearly 7 million cans of Spam a year, 11,000 cans per day, an average of about six for every man, woman and child. Spam fried rice is a local classic.
http://www.azstarnet.com/dailystar/relatedarticles/14264.php http://www.letsgo.com/HAW/02-LifeTimes-57
From dictionary.com: spam (n): Unsolicited e-mail, often of a commercial
nature, sent indiscriminately to multiple mailing lists, individuals, or newsgroups; junk e-mail.
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SPAM
© Copyright 2005– Chesapeake NetCraftsmen
The Problem
"Spamming is the scourge of electronic-mail and newsgroups on the Internet. It can seriously interfere with the operation of public services, to say nothing of the effect it may have on any individual's e-mail mail system. ... Spammers are, in effect, taking resources away from users and service suppliers without compensation and without authorization."
-- Vint Cerf, Senior Vice President, MCI
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Why All the Fuss?
Loss of Productivity Discouraged Users Loss of Efficiency Legal Issues Communications Quality Business Continuity Company Reputation
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Fraud
Spammers know that in survey after survey, the overwhelming majority (often approaching 95%) of recipients don't want to receive their messages.
In many cases, ISPs and consumers have set up "filters" to help dispose of SPAM. While filters often consume more resources at the ISP, making mail delivery and web surfing slower, they can sometimes help end-users cope a little bit better.
Another common trick that spammers use is to forge the headers of messages, making it appear as though the message originated elsewhere, again providing a convenient target.
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Profile of a SPAMer
Used ~20 computers, to send SPAM to list of over 250 million addresses, ~650,000 message/hour
Controlled/used ~200 servers in Michigan, Texas and Asia, routing primarily through overseas ISPs.
Charge to send one solicitation to his entire list: up to $22,000
"When you're sending out 250 million e-mails, even a blind squirrel will find a nut.“
Mr. Ralsky has amassed his fortune with an e-mail response rate of less than one quarter of one percent
During the time he was in business, spam has increased from 8% to 36% of all electronic mail. It is expected to increase to 50% by 2005.
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Profile
Sanford Wallace and his companies, SmartBot.net Inc. of Richboro, Pa., and Seismic Entertainment Productions Inc. of Rochester, N.H., are required by the agreement to send online ads only to people who visit their Web sites.
Wallace used spyware to infiltrate computers, overwhelming them with ads and other programs. Then, he tried to sell programs he claimed would fix the problems.
He headed a company called Cyber Promotions that sent as many as 30 million junk e-mails daily to consumers, earning him the nicknames “Spam King” and “Spamford”. He left the company after lawsuits from America Online and CompuServe
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Statistics
Early 2003, spam accounted for about 50% of all e-mail
Postini, (Redwood City, CA) anti-spam firm, scans ~400 million messages/day
End of 2003, grown to roughly 75 percent. Throughout 2004, spam accounted for 75 to 80
percent of all e-mail (Postini) Denver-based MX Logic reported spam at ~77 percent
of the messages scanned in 2004. In December 2003, spam accounted for 67 percent of
messages.
© Copyright 2003 – Chesapeake NetCraftsmen, LLC
Stopping Spam
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What Can We Do?
1. Make it illegal to send spam
2. Policy, Policy, Policy
3. Technically blocking spam
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The Legal Avenue
# CAN-SPAM Act of 2003 (S. 877) (Burns-Wyden) Signed, Dec. 16, 2003 Illegal to falsify the "from" and "subject" lines of e-mail Required senders of bulk e-mail to include a working
"unsubscribe" link The law doesn't allow individual e-mail users to sue
spammers AOL reported a drop-off both in the volume of e-mail hitting
its network and in the amount of spam delivered to users' inboxes in 2004.
Fielded 1.6 billion e-mail messages in 2004, down from 2.1 billion in 2003
March 2004, file several lawsuits targeting some of the most prolific spammers, more to follow
Approximately 20 states have local laws -http://www.spamlaws.com/state/summary.html
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The Legal Avenue
Summary of Bills in front of 108th Congress (109th now) # Anti-Spam Act of 2003 (H.R. 2515) (Wilson) # Ban on Deceptive Unsolicited Bulk Electronic Mail Act of
2003 (S. 1052) (Bill Nelson) # Computer Owners' Bill of Rights (S. 563) (Dayton) # Criminal Spam Act of 2003 (S. 1293) (Hatch) # Reduction in Distribution of Spam Act of 2003 (H.R. 2214)
(Burr) # REDUCE Spam Act of 2003 (H.R. 1933) (Lofgren) # Stop Pornography and Abusive Marketing Act (S. 1231)
(Schumer) # Wireless Telephone Spam Protection Act (H.R. 122)
(Holt) Resource at http://www.spamlaws.com
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Stopping Spammers From Sending Spam
Simple Mail Transfer Protocol (SMTP) is used to transfer e-mail across the Internet
Designed when the Internet was small and friendly
Very efficient at forwarding and delivering email. Not intended to manage content, Post Office
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The ISP
Why Can't the ISP Just Block it? Data movers, what would they block? Often it is difficult for ISPs to block
spam to everyone. Expensive to implement Difficult to maintain Often inconvenient for users
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Kill the Relay
'Simple Mail Transfer Protocol‘, used does not check passwords or any other sort of access when it is accepting messages for delivery.
If a spammer connects to your email server all they have to do is give it a list of addresses. The MTA then 'fans out' the lists of email addresses into real attempts to connect to remote sites.
While this simple technique works fairly well, not all mail server packages support this feature.
Third-party software, such as Lyris MailShield, can add anti-relay security to servers that do not support filtering of TCP/IP addresses or other anti-relay techniques.
If your company has employees who travel or telecommute, you may wish to only allow specific "From:" addresses to prevent unauthorized relaying.
Use a mail proxy server with anti-relay features, and a regular mail server that is protected by a firewall, internal TCP/IP address, or port-moving technique.
© Copyright 2005– Chesapeake NetCraftsmen
Stopping Spammers From Sending Spam (2)
Open mail relays are a serious impediment to stopping spam!
Internet
spammer.com
openrelay.com
victim.com
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Address Munging
Address munging is the act of modifying one's email address so that email sent to that address will not be delivered to the person doing the modifications.
The Jargon File defines 'mung' as `Mash Until No Good', probably originating at MIT.
Munging DOES NOT MEAN MAKING YOURSELF ANONYMOUS
Trying to hide your identity by faking your email address simply does not work.
Trying to hide from spammers by changing the "name" or "real name" portion of your posted address also does not work.
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Should I “unsubscribe”?
Often a plot to appear responsible Spammers would be out of business
very quickly if everyone unsubscribed. Unsubscribing provides proof that
your e-mail address is active.
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What Can I do?
Forward a message with your spam complaint to the Internet Service Provider (ISP) that hosts the spammer's e-mail account.
For example, if you received spam from [email protected], then go to the Web site www.llama-boy.com and look for a "contact us" page.
Often ISPs have an e-mail account called "abuse" for such purposes.
You could also try [email protected] or [email protected].
Try to verify what the correct address is first so you don't waste anyone else's time.
Reputable ISPs will investigate spammers
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Mail Clients
Outlook Automatically flag suspect email Place it in the “Junk Mail”. Users can flag email and move to Junk Email “Junk” all email from a domain can be marked as Junk.
Netscape Netscape Mail automatically detects incoming messages that appear to
be spam. When it detects a message that appears to be unwanted, it marks the
message's Junk Status column with a special junk mail icon. Need to “teach” Netscape Mail what is spam
Yahoo Web Email In "Mail Options“, provides address blocking features, filters and spam
protection Hotmail
Various anti-spam features, including three automatic levels
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Third Party Add-ons
Cloudmark offers a plug-in for Outlook and Outlook Express that allows you to mark specific emails as spam and registers those emails on its network. When enough people mark a message as spam it automatically deletes the message from every member’s inbox.
SpamArrest takes a different approach. It filters all your mail through its mail server and only forwards mail from those senders who have been approved by you or those that have been challenged to type in a special keyword.
MailBlocks: Offers a web-based email service like Hotmail but it has a built in challenge/response system similar to the one employed by the SpamArrest service.
© Copyright 2005– Chesapeake NetCraftsmen
Ban header text
Many spam programs include telltale text in the headers of messages they send. For example: "public.com" or "friend@public."
Other examples of telltale text and tags include: "savetrees.com," "relay.comanche.denmark," and "x-advert.“
If you ban header text, you can eliminate a significant amount of spam created by automated programs.
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Filtering
In addition to filtering TCP/IP addresses and header text, it is also important that your server or anti-spam software filter body text.
The email address given in the body of the text may not be the same as the "From:" address, an indicator that the mail could be spam.
Filtering body text and subject lines also allows you protection against the recent Melissa virus since "Melissa-tainted" email often includes the following telltale information:
* A subject line of: "Important Message From [sender's name]" * A body with the following content: "Here is that document you
asked for ... don't show anyone else ;-)"
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Tarpit spammers
Tarpitting involves creating delays that slow down the mail-sending sessions of spammers.
Evidence shows that when tarpitting slows down mail-sending from a server that is used for unauthorized relaying, the owner of the server may (1) become aware of the unauthorized relaying if he or she wasn't aware of it before and (2) adopt higher security measures to avoid being tarpitted.
Besides tarpitting specific domains, one might also tarpit users that attempt to send mail to large numbers of people. Spam software works by sending a single message, and a huge BCC (blind carbon copy) list to the server for delivery.
If you know that your customers (in the case of an ISP) or employees do not need to send mail to more than 20 recipients per message, you might tarpit a mail-sending session that attempts to send mail to 50 recipients.
Some anti-spam software also allows you to tarpit specific TCP/IP addresses.
© Copyright 2005– Chesapeake NetCraftsmen
Enforce Email Standards
Internet email standards basically state the following:
* All mail must include a "From:" header. * All mail must include "To:" header. * All mail servers must have a reverse DNS host entry.
Spammers typically violate Internet mail standards.
Anti-spam software like Lyris MailShield allows you to modify the rules for filtering mail and send an explanation message to users that their mail was rejected
Although not explicitly stated, valid host values for the HELO command are also encouraged by the Internet standards.
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Tracking, Blocking, and Filtering Spam
© Copyright 2005– Chesapeake NetCraftsmen
Example: Standard E-Mail Message
Date: Tue, 25 Mar 1997 12:00:48 -0500 (EST) From: John Smith <[email protected]> To: Joe Roundy <[email protected]> Subject: Hello
This is a perfectly good e-mail message.
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Example: All Message Headers
From [email protected] Wed Jan 15 12:00:50 2003 Return-Path: jsmith Received: (from jsmith@localhost) by
netcraftsmen.net (8.6.12/8.6.9) id MAA00135; Wed, 15 Jan 2003 12:00:48 -0500
Date: Wed, 15 Jan 2003 12:00:48 -0500 (EST) From: John Smith <[email protected]> To: Joe Roundy <[email protected]> Subject: Hello Message-ID: <Pine.LNX.3.91.970325115954.130A-
[email protected]> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Status: RO X-Status:
This is a perfectly good e-mail message.
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Example: Forged Mail Headers
Date: Tue, 25 Mar 1997 12:25:57 -0500
From: [email protected]
Hello. This is a really horrible piece of forged e-mail.
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Forged Mail Headers: Who Is Responsible?
From [email protected] Wed Jan 15 12:26:29 2003 Return-Path: [email protected] Received: from nowhere.com (jsmith@localhost [127.0.0.1]) by
netcraftsmen.net (8.6.12/8.6.9) with SMTP id MAA00153 for jroundy; Wed, 15 Jan 2003 12:25:57 -0500
Date: Wed, 15 Jan 2003 12:25:57 -0500 From: [email protected] Message-Id: <[email protected]> Apparently-To: [email protected] Status: RO X-Status:
Hello. This is a really horrible piece of forged e-mail.
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Example: Actual Spam
Return-Path: <[email protected]>Received: from mindless.com ([202.7.209.122]) by netcraftsmen.net
(netcraftsmen.net mail service) with SMTP id 18xLfy7t43Nl3oW0 Sun, 12 Jan 2003 11:46:12 -0500 (EST)
Received: from 115.131.120.61 ([115.131.120.61]) by webmail.halftomorrow.com with esmtp; Sun, 12 Jan 2003 04:47:29 -1100
Received: from unknown (HELO mxs.perenter.com) (190.44.249.166) by public.micromail.com.au with NNFMP; Sat, 11 Jan 2003 17:46:47 +0900
Received: from unknown (85.121.248.18) by asx121.turbo-inline.com with asmtp; 12 Jan 2003 02:46:05 +1000
Received: from [98.109.171.85] by external.newsubdomain.com with local; 12 Jan 2003 12:45:23 -0300
Received: from unknown (HELO qnx.mdrost.com) (205.236.177.234) by nntp.pinxodet.net with NNFMP; Sun, 12 Jan 2003 09:44:41 -0500
<- SNIP ->
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Mail Filtering
Modern mail software packages have features to filter mail based on:Message headersMessage bodySending host, including:
• IP address• DNS lookup• SMTP responses
Many more …
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Real-Time Blocking Lists (RBL)
RBLs provide efficient and consensual blocking of mail hosts known to harbor spammers
Examples include:http://www.dnsbl.orghttp://relays.osirusoft.com
Caution is advised when choosing your RBL!
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Example: RBL
1. Spammer starts to send spam to the victim
Internet
spammer.com
rbl.com
victim.com
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Example: RBL (2)
2. Victim checks with RBL to determine if spamking.net is a known spammer
Internet
spammer.com
rbl.com
victim.com
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Example: RBL (3)
3. RBL responds that spamking.net is a confirmed spammer
Internet
spammer.com
rbl.com
victim.com
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Example: RBL (4)
4. Victim blocks mail transmission
Internet
spammer.com
rbl.com
victim.comX
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Regular Expression Matching
Searches incoming messages for patterns of text that are known to be used by spammers
Improper sensitivity levels may miss spam or mark legitimate messages as spam
Very commonly used method
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Example: Regular Expression Matching
Set up regular expression filter Search for the regular expression:
“Buy Widgets”“Hot Date!”Drawbacks?
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Regular Expression Matching: Hit Lists
Method used to avoid mislabeling legitimate messages
Every regular expression “hit” is associated with some number of “points”
When a threshold is met, the mail is marked as spam
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Text Searches Vs. Language
Computers search text for specific strings
People read text and comprehend language
How do we program a computer to recognize language in terms that it can understand?
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Bayesian Filtering
Filters spam based on a statistical analysis of the contents
Calculate the probability of a message being spam based on its contents and previous email.
Learns from spam and from good mail Scoring content-based spam filters look for words and
other characteristics typical of spam. Every characteristic element is assigned a score, and
a spam score for the whole message is computed from the individual score
Adaptive
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Implementing Bayesian Filtering
Build two collections of mail:SpamNon-spam
Collections should be at least 4000 messages for accurate results
Filter breaks apart messages into a collection of tokens and creates a hash
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Compare E-Mail to the Token Hash
As e-mail is received:Separate the e-mail into tokensCompare it to the hashBased on the outcome, mark it
appropriately
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Spam Filtering Architectures and Examples
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Example Network: No Filtering
MicrosoftExchange
Server
Firew all
Mail Client
Mail Client
Mail Client
Internet
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Example Network: Mail Relay
MicrosoftExchange
Server
Firew all
Mail Client
Mail Client
Mail Client
Internet
Mail Relay
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Preparing the Mail Relay
The mail relay should:Run on a stable, fault-tolerant
operating systemOnly be running mail applicationsBe hardened against attack
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Example Network: Redundant Relays
MicrosoftExchange
Server
Firew all
Mail Client
Mail Client
Mail Client
Internet
Mail Relay Mail Relay
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Relay Filtering Options
MailScannerhttp://www.mailscanner.info
Separates incoming and outgoing mail into separate queues
Runs external anti-virus and spam filtering software to scan incoming mail
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MailScanner Architecture
Outbound Queue
Anti-Virus Spam Filter
Inbound Queue MailScannerInbound QueueMailScanner
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Spam Filtering Options
SpamAssassinhttp://www.spamassassin.org
Supports:RBLRegular expression matchingText analysisBayesian filtering
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Example Network: Outgoing Mail
MicrosoftExchange
Server
Firew all
Mail Client
Mail Client
Mail Client
Internet
Mail Relay Mail Relay
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Questions
Joe Roundy
Senior Security Consultant
Resources http://www.letsgo.com/HAW/02-LifeTimes-57 http://www.spamfilterreview.com/spam-statistics.html http://www.spamlaws.com http://email.about.com/cs/bayesianfilters/a/bayesian_filter.htm http://www.spamfilterreview.com/index.html