CIT 380: Securing Computer SystemsSlide #1 CIT 380: Securing Computer Systems Web Security

CIT 380: Securing Computer SystemsSlide #2 Topics 1.HTTP 2.Web Input 3.Web Application Vulnerabilities 4.Client-side Attacks 5.Finding Web Vulnerabilities

CIT 380: Securing Computer SystemsSlide #3 Web Transactions Web Browser OS Web Server Network HTTP Request HTTP Response

CIT 380: Securing Computer SystemsSlide #4 HTTP: HyperText Transfer Protocol Simple request/respond protocol –Request methods: GET, POST, HEAD, etc. –Protocol versions: 1.0, 1.1 Stateless –Each request independent of previous requests, i.e. request #2 doesn’t know you auth’d in #1. –Applications responsible for handling state.

CIT 380: Securing Computer SystemsSlide #5 HTTP Request GET HTTP/1.1 Host: User-Agent: Mozilla/5.0 (Windows NT 5.1) Gecko/ Firefox/ Accept: text/html, image/png, */* Accept-Language: en-us,en;q=0.5 Cookie: rememberme=true; PREF=ID=21039ab4bbc49153:FF=4 MethodURL Protocol Version Headers Blank Line No Data for GET method

CIT 380: Securing Computer SystemsSlide #6 HTTP Response HTTP/ OK Cache-Control: private Content-Type: text/html Server: GWS/2.1 Date: Fri, 13 Oct :16:30 GMT... (page data)... Protocol VersionHTTP Response Code Headers Blank Line Web Page Data

CIT 380: Securing Computer SystemsSlide #7 Different Perspectives Client Side HTTP requests may reveal private info. HTTP responses may reveal private info. HTTP responses may include malicious code (Java, ActiveX, Javascript) Server Side HTTP requests may contain malicious input. HTTP requests may have forged authentication. HTTP responses may be intercepted.

CIT 380: Securing Computer SystemsSlide #8 Web-based Input Client and Server Perspectives Types of Input –URL parameters –HTML –Cookies –Javascript Cross-Site Scripting

CIT 380: Securing Computer SystemsSlide #9 URL Format : / ? –Whitespace marks end of URL separates userinfo from host –“?” marks beginning of query string –“&” separates query parameters –%HH represents character with hex values –ex: %20 represents a space

CIT 380: Securing Computer SystemsSlide #10 URL Parameters Client controls query-string –Cannot limit values to those specified in form Any character can be URL-encoded –Even if it doesn’t need to be. Any valid format may be used to disguise true destination of URL

CIT 380: Securing Computer SystemsSlide #11 URL Obfuscation IP address representations –Dotted quad (decimal, octal, hexadecimal) –Hexadecimal without dots (with left padding) –dword (32-bit int) Examples: – (dotted quad) –0xDEDA83B7130E (hexadecimal + padding) – (dword)

CIT 380: Securing Computer SystemsSlide #12 HTML Special Characters “<“ begins a tag “>” ends a tag –some browsers will auto-insert matching “<“ “&” begins a character entity –ex: < represents literal “<“ character Quotes(‘ and “) used to enclose attribute values

CIT 380: Securing Computer SystemsSlide #13 Character Set Encoding Default: ISO (Latin-1) Char sets dictate which chars are special UTF-8 allows multiple representations Force Latin-1 encoding of web page with: –

CIT 380: Securing Computer SystemsSlide #14 Hidden Fields Used to propagate data between HTTP requests since protocol is stateless Clearly visible in HTML source Form can be copied, modified to change hidden fields, then used to invoke script

CIT 380: Securing Computer SystemsSlide #15 Cookies Server to Client Content-type: text/html Set-Cookie: foo=bar; path=/; expires Fri, 20-Feb :59:00 GMT Client to Server Content-type: text/html Cookie: foo=bar

CIT 380: Securing Computer SystemsSlide #16 Web Input Summary Client Side URLs may not lead where they seem to. Cookies can be used to track your browsing. Pages may include malicious code (Java, ActiveX, Javascript) Server Side Cookies aren’t confidential. Hidden fields aren’t secret. Client may use own forms. URLs can have any format. POST data can have any format. Cookies can have any format.

CIT 380: Securing Computer SystemsSlide #17 Web Application Vulnerabilities Input-based Security Problems –Injection Flaws –Insecure Remote File Inclusion –Unvalidated Input Authentication and Authorization –Authentication –Access Control –Cross-Site Scripting Other Bugs –Error Handling and Information Leakage –Insecure Storage –Insecure Communications

CIT 380: Securing Computer SystemsSlide #18 Injection Injection attacks trick an application into including unintended commands in the data send to an interpreter. Interpreters –Interpret strings as commands. –Ex: SQL, shell (cmd.exe, bash), LDAP, XPath Key Idea –Input data from the application is executed as code by the interpreter.

CIT 380: Securing Computer SystemsSlide #19 SQL Injection 1.App sends form to user. 2.Attacker submits form with SQL exploit data. 3.Application builds string with exploit data. 4.Application sends SQL query to DB. 5.DB executes query, including exploit, sends data back to application. 6.Application returns data to user. Attacker Web Server DB Server Firewall User Pass ‘ or 1=1--

CIT 380: Securing Computer SystemsSlide #20 SQL Injection in PHP $link = mysql_connect($DB_HOST, $DB_USERNAME, $DB_PASSWORD) or die ("Couldn't connect: ". mysql_error()); mysql_select_db($DB_DATABASE); $query = "select count(*) from users where username = '$username' and password = '$password'"; $result = mysql_query($query);

CIT 380: Securing Computer SystemsSlide #21 SQL Injection Attack #1 Unauthorized Access Attempt: password = ’ or 1=1 -- SQL statement becomes: select count(*) from users where username = ‘user’ and password = ‘’ or 1=1 -- Checks if password is empty OR 1=1, which is always true, permitting access.

CIT 380: Securing Computer SystemsSlide #22 SQL Injection Attack #2 Database Modification Attack: password = foo’; delete from table users where username like ‘% Database executes two SQL statements: select count(*) from users where username = ‘user’ and password = ‘foo’ delete from table users where username like ‘%’

CIT 380: Securing Computer SystemsSlide #23 Impact of SQL Injection SELECT SSN FROM USERS WHERE UID=‘$UID’ INPUTRESULT 5Returns info for user with UID 5. ‘ OR 1=1--Returns info for all users. ‘ UNION SELECT Field FROM Table WHERE 1=1-- Returns all rows from another table. ‘;DROP TABLE USERS-- Deletes the users table. ‘;master.dbo.xp_cmd shell ‘cmd.exe format c: /q /yes’ -- Formats C: drive of database server if you’re running MS SQL Server and extended procedures aren’t disabled.

CIT 380: Securing Computer SystemsSlide #24 Mitigation: Prepared Queries require_once 'MDB2.php'; $mdb2 =& MDB2::factory($dsn, $options); if (PEAR::isError($mdb2)) { die($mdb2->getMessage()); } $sql = “SELECT count(*) from users where username = ? and password = ?”; $types = array('text', 'text'); $sth = $mdb2->prepare($sql, $types, MDB2_PREPARE_MANIP); $data = array($username, $password); $sth->execute($data);