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Web Security

Web Security. Chapter 7. Objectives. Protect e-mail systems Identify World Wide Web vulnerabilities Secure Web communications. cs490ns-cotter. 2. How E-Mail Works. Defined in RFC 822 Use two Internet protocols to send and receive messages

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Web Security

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  1. Web Security Chapter 7 Web Security

  2. Objectives Protect e-mail systems Identify World Wide Web vulnerabilities Secure Web communications cs490ns-cotter 2

  3. How E-Mail Works Defined in RFC 822 Use two Internet protocols to send and receive messages Simple Mail Transfer Protocol (SMTP) handles outgoing mail and Either Post Office Protocol (POP3 for the current version) handles incoming mail Or Internet Mail Access Protocol (IMAP4 is current) The SMTP server on most machines uses sendmail to do the actual sending; this queue is called the sendmail queue cs490ns-cotter 3

  4. E-mail Architecture Mail Server Sender Recipient Remote Access server Mail server cs490ns-cotter 4

  5. E-mail Architecture MGA SMTP Sender Recipient Internet Retrieval Protocol Delivery Protocol 5 cs490ns-cotter

  6. How E-Mail Works Sendmail tries to resend queued messages periodically (about every 15 minutes) Downloaded messages are erased from POP3 server (by default) Deleting retrieved messages from the mail server and storing them on a local computer may make it difficult to manage messages from multiple computers Internet Mail Access Protocol (current version is IMAP4) is a more advanced protocol that solves many problems E-mail can remain on the e-mail server cs490ns-cotter 6

  7. How E-Mail Works (cont) E-mail attachments are often in binary format (word processing documents, spreadsheets, sound files, pictures, etc.) But SMTP is text only. Multipurpose Internet Mail Extensions (MIME) Rfc 1341, 1521, 1522 Non-text documents must be converted into text format before being transmitted Three bytes from the binary file are extracted and converted to four text characters cs490ns-cotter 7

  8. E-Mail Vulnerabilities Several e-mail vulnerabilities can be exploited by attackers: Malware Spam Hoaxes cs490ns-cotter 8

  9. Malware Because of its ubiquity, e-mail has replaced floppy disks as the primary carrier for malware E-mail is the malware transport mechanism of choice for two reasons: Because almost all Internet users have e-mail, it has the broadest base for attacks Malware can use e-mail to propagate itself cs490ns-cotter 9

  10. Malware (cont) A worm can enter a user’s computer through an e-mail attachment and send itself to all users listed in the address book or attach itself as a reply to all unread e-mail messages E-mail clients can be particularly susceptible to macro viruses A macro is a script that records the steps a user performs A macro virus uses macros to carry out malicious functions cs490ns-cotter 10

  11. Spam The amount of spam (unsolicited e-mail) that flows across the Internet is difficult to judge The US Congress passed the Controlling the Assault of Non-Solicited Pornography and Marketing Act of 2003 (CAN-SPAM) in late 2003 cs490ns-cotter 11

  12. Spam (cont) According to a Pew Memorial Trust survey, almost half of the approximately 30 billion daily e-mail messages are spam Spam is having a negative impact on e-mail users: 25% of users say the ever-increasing volume of spam has reduced their overall use of e-mail 52% of users indicate spam has made them less trusting of e-mail in general 70% of users say spam has made being online unpleasant or annoying cs490ns-cotter 12

  13. E-Mail Encryption Two technologies used to protect e-mail messages as they are being transported: Secure/Multipurpose Internet Mail Extensions Pretty Good Privacy cs490ns-cotter 13

  14. S/MIME Secure/Multipurpose Internet Mail Extensions Initial specification 10/95 (rfc 1847) V2 widely deployed 3/98 (rfc 2311) V3 available 6/99 (rfc 2633) Protocol that adds digital signatures and encryption to Multipurpose Internet Mail Extension (MIME) messages cs490ns-cotter 14

  15. S/MIME Functionality Enveloped Data (Message Privacy) Signed Data (Digital Signatures, Tamper Detection) Clear-signed Data (Interoperability) Signed and Enveloped Data (Everything!) cs490ns-cotter 15

  16. Pretty Good Privacy (PGP) Functions much like S/MIME by encrypting messages using digital signatures A user can sign an e-mail message without encrypting it, verifying the sender but not preventing anyone from seeing the contents Originally released as freeWare. Now available as a commercial product GNU Privacy Guard (GPG) available for free. Two versions are generally INcompatible. cs490ns-cotter 16

  17. PGP (cont) Stores private keys on a local “keyring” file Uses a passphrase to encrypt the keyring on the local computer Passphrase: A longer and more secure version of a password Typically composed of multiple words More secure against dictionary attacks cs490ns-cotter 17

  18. PGP Encryption Message Compression Reduces patterns and enhances resistance to cryptanalysis Session key (a one-time-only secret key – 128 bit number) This key is a number generated from random movements of the mouse and keystrokes typed cs490ns-cotter 18

  19. PGP Services Digital Signature Uses DSS / SHA or RSA / SHA SHA-1 used to create message digest. RSA / DSS used to encrypt digest using sender’s private key Message Encryption Session Key generated. Message encrypted with CAST-128 / IDEA / 3DES Session key encrypted using D-H or RSA and recipient’s public key Compression Uses zip algorithm cs490ns-cotter 19

  20. PGP Encryption Sender 4#*l, $@2ug D86qL Mt m fr lnch Tsdy Meet me for lunch Tuesday compress encrypt Recipient’s Public Key Recipient 4#*l, $@2ug D86qL Session Key cs490ns-cotter 20

  21. WWW Vulnerabilities WWW Phishing Mobile Code Javascript, Java, ActiveX/COM Cookies SQL Injection Dynamic content can also be used by attackers Sometimes called repurposed programming (using programming tools in ways more harmful than originally intended) cs490ns-cotter 21

  22. HTML • Hypertext markup language (HTML) • Describes the content and formatting of Web pages • Rendered within browser window • HTML features • Static document description language • Supports linking to other pages and embedding images by reference • User input sent to server via forms • HTML extensions • Additional media content (e.g., PDF, video) supported through plugins • Embedding programs in supported languages (e.g., JavaScript, Java) provides dynamic content that interacts with the user, modifies the browser user interface, and can access the client computer environment Web Security

  23. Phishing • Forged web pages created to fraudulently acquire sensitive information • User typically solicited to access phished page from spam email • Most targeted sites • Financial services (e.g., Citibank) • Payment services (e.g., PayPal) • Auctions (e..g, eBay) • 45K unique phishing sites detected monthly in 2009 [APWG Phishing Trends Reports] • Methods to avoid detection • Misspelled URL • URL obfuscation • Removed or forged address bar Web Security

  24. Phishing Example http://www.anti-phishing.com Web Security

  25. URL Obfuscation http://www.anti-phishing.com • Properties of page in previous slide • Actual URL different from spoofed URL displayed in address bar • URL escape character attack • Old versions of Internet Explorer did not display anything past the Esc or null character • Displayed vs. actual sitehttp://trusted.com%01%00@malicious.com • Unicode attack • Domains names with Unicode characters can be registered • Identical, or very similar, graphic rendering for some characters • E.g., Cyrillic and Latin “a” • Phishing attack on paypal.com • Current version of browsers display Punycode, an ASCII-encoded version of Unicode: www.xn--pypal-4ve.com Web Security

  26. Mobile Code • What is mobile code? • Executable program • Sent via a computer network • Executed at the destination • Examples • JavaScript • ActiveX • Java Plugins • Integrated Java Virtual Machines Web Security

  27. JavaScript • Scripting language interpreted by the browser • Code enclosed within <script> … </script> tags • Defining functions: <script type="text/javascript"> function hello() { alert("Hello world!"); } </script> • Event handlers embedded in HTML <img src="picture.gif" onMouseOver="javascript:hello()"> • Built-in functions can change content of window window.open("http://brown.edu") • Click-jacking attack <a onMouseUp="window.open(′http://www.evilsite.com′)" href="http://www.trustedsite.com/">Trust me!</a> Web Security

  28. ActiveX vs. Java ActiveX Control Java Applet • Windows-only technology runs in Internet Explorer • Binary code executed on behalf of browser • Can access user files • Support for signed code • An installed control can be run by any site (up to IE7) • IE configuration options • Allow, deny, prompt • Administrator approval Platform-independent via browser plugin Java code running within browser Sandboxed execution Support for signed code Applet runs only on site where it is embedded Applets deemed trusted by user can escape sandbox Web Security

  29. Embedding an ActiveX Control <HTML> <HEAD> <TITLE> Draw a Square </TITLE> </HEAD> <BODY> Here is an example ActiveX reference: <OBJECT ID="Sample“ CODEBASE="http://www.badsite.com/controls/stop.ocx" HEIGHT="101“ WIDTH="101“ CLASSID="clsid:0342D101-2EE9-1BAF-34565634EB71" > <PARAM NAME="Version" VALUE=45445"> <PARAM NAME="ExtentX" VALUE="3001"> <PARAM NAME="ExtentY" VALUE="2445"> </OBJECT> </BODY> </HTML> Web Security

  30. Authenticode in ActiveX Malicious Mobile Code, by R. Grimes, O’Reilly Books • This signed ActiveX control ask the user for permission to run • If approved, the control will run with the same privileges as the user • The “Always trust content from …” checkbox automatically accepts controls by the same publisher • Probably a bad idea Web Security

  31. ActiveX Security cs490ns-cotter 31

  32. Classic ActiveX Exploits • Exploder and Runner controls designed by Fred McLain • Exploder was an ActiveX control for which he purchased a VeriSign digital signature • The control would power down the machine • Runner was a control that simply opened up a DOS prompt While harmless, the control easily could have executed format C: or some other malicious command • http://www.halcyon.com/mclain/ActiveX/Exploder/FAQ.htm • Quicken exploit by a German hacking club • Intuit’s Quicken is personal financial management tool • Can be configured to auto-login to bank and credit car sites • The control that would search the computer for Quicken and execute a transaction that transfers user funds to their account Web Security

  33. Cookies • Cookies are a small bit of information stored on a computer associated with a specific server • When you access a specific website, it might store information as a cookie • Every time you revisit that server, the cookie is re-sent to the server • Effectively used to hold state information over sessions • Cookies can hold any type of information • Can also hold sensitive information • This includes passwords, credit card information, social security number, etc. • Session cookies, non-persistent cookies, persistent cookies • Almost every large website uses cookies Web Security

  34. More on Cookies • Cookies are stored on your computer and can be controlled • However, many sites require that you enable cookies in order to use the site • Their storage on your computer naturally lends itself to exploits (Think about how ActiveX could exploit cookies...) • You can (and probably should) clear your cookies on a regular basis • Most browsers will also have ways to turn off cookies, exclude certain sites from adding cookies, and accept only certain sites' cookies • Cookies expire • The expiration is set by the sites' session by default, which is chosen by the server • This means that cookies will probably stick around for a while Web Security

  35. SQL Injection Attack • Many web applications take user input from a form • Often this user input is used literally in the construction of a SQL query submitted to a database. For example: SELECT user FROM table WHERE name = ‘user_input’; • An SQL injection attack involves placing SQL statements in the user input Web Security

  36. SQL Syntax SELECT column_name(s) or * FROM table_name WHEREcolumn_name operator value SELECT statement is used to select data FROM one or more tables in a database Result-set is stored in a result table WHERE clause is used to filter records Storage Confidentiality

  37. Login Authentication Query • Standard query to authenticate users: select * from users where user='$usern' AND pwd='$password' • Classic SQL injection attacks • Server side code sets variables $username and $passwd from user input to web form • Variables passed to SQL query select * from users where user='$username' AND pwd='$passwd' • Special strings can be entered by attacker select * from users where user='M' OR '1=1' AND pwd='M' OR '1=1' • Result: access obtained without password Web Security

  38. Securing Web Communications Most common secure connection uses the Secure Sockets Layer/Transport Layer Security protocol One implementation is the Hypertext Transport Protocol over Secure Sockets Layer cs490ns-cotter 38

  39. SSL / TLS SSL protocol developed by Netscape to securely transmit documents over the Internet Uses private key to encrypt data transferred over the SSL connection Version 3.0 is most widely supported version Personal Communications Technology (PCT), developed by Microsoft, is similar to SSL cs490ns-cotter 39

  40. SSL / TLS TLS protocol guarantees privacy and data integrity between applications communicating over the Internet An extension of SSL; they are often referred to as SSL/TLS SSL/TLS protocol is made up of two layers cs490ns-cotter 40

  41. SSL / TLS TLS Handshake Protocol allows authentication between server and client and negotiation of an encryption algorithm and cryptographic keys before any data is transmitted FORTEZZA is a US government security standard that satisfies the Defense Messaging System security architecture Has cryptographic mechanism that provides message confidentiality, integrity, authentication, and access control to messages, components, and even systems cs490ns-cotter 41

  42. HTTPS One common use of SSL is to secure Web HTTP communication between a browser and a Web server This version is “plain” HTTP sent over SSL/TLS and named Hypertext Transport Protocol over SSL Generally designated HTTPS, which is the extension to the HTTP protocol that supports it Whereas SSL/TLS creates a secure connection between a client and a server over which any amount of data can be sent security, HTTPS is designed to transmit individual messages securely cs490ns-cotter 42

  43. References: S/MIME – PGP RFCs 2311-2315 RFC 2015, 2440, 3156 Cryptography and Network Security – Stallings openPGP RFC 4880 TLS RFC 2246 cs490ns-cotter 43

  44. Summary Protecting basic communication systems is a key to resisting attacks E-mail attacks can be malware, spam, or hoaxes Web vulnerabilities can open systems up to a variety of attacks A Java applet is a separate program stored on the Web server and downloaded onto the user’s computer along with the HTML code cs490ns-cotter 44

  45. Summary ActiveX controls present serious security concerns because of the functions that a control can execute A cookie is a computer file that contains user-specific information CGI is a set of rules that describe how a Web server communicates with other software on the server The popularity of IM has made this a tool that many organizations are now using with e-mail cs490ns-cotter 45

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