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One-Way Hacking: Futility of Firewalls in Web Hacking

One-Way Hacking: Futility of Firewalls in Web Hacking. JD Glaser, Saumil Shah Foundstone Inc. Typical Web Application set-up. SQL Database. HTTP request (cleartext or SSL). Firewall. Web Client. Web Server. Web app. DB. Web app. DB. Web app. Web app. HTTP reply

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One-Way Hacking: Futility of Firewalls in Web Hacking

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  1. One-Way Hacking:Futility of Firewalls in WebHacking JD Glaser, Saumil Shah Foundstone Inc.

  2. Typical Web Application set-up SQL Database HTTP request (cleartext or SSL) Firewall Web Client Web Server Web app DB Web app DB Web app Web app HTTP reply (HTML, Javascript, VBscript, etc) • Apache • IIS • Netscape • etc… • Plugins: • Perl • C/C++ • JSP, etc • Database connection: • ADO, • ODBC, etc.

  3. Traditional Hacking…Limitations • Modern network architectures are getting more robust and secure. • Firewalls being used in almost all network roll-outs. • OS vendors learning from past mistakes (?) and coming out with patches rapidly. • Increased maturity in coding practices.

  4. Utility of Firewalls • Hacks on OS network services prevented by firewalls. Web Server Web app DB Web app DB Web app Web app wu-ftpd X Sun RPC X NT ipc$ X

  5. Utility of Firewalls • Internal back-end application servers are on a non-routable IP network. (private addresses) Web Server Web app DB Web app DB Web app Web app X

  6. Utility of Firewalls • Outbound access restricted. Why would a web server telnet out? Web Server Web app DB Web app DB Web app Web app X

  7. Futility of Firewalls • E-commerce / Web hacking is unfettered. • Web traffic is the most commonly allowed of protocols through Internet firewalls. • Why fight the wall when you’ve got an open door? • HTTP is perceived as “friendly” traffic. • Content/Application based attacks are still perceived as rare.

  8. The Web Hacker’s Toolbox Essentially, all a web hacker needs is … • a web browser, • an Internet connection, • … and a clear mind.

  9. Firewalls cannot prevent… Web Client Web Server • URL Interpretation Attacks. web server mis-configuration

  10. Firewalls cannot prevent… Web Client Web Server Web app Web app Web app Web app • Input Validation attacks. URL Interpretation attacks poor checking of user inputs

  11. Firewalls cannot prevent… Web Client Web Server Web app DB Web app DB Web app Web app • SQL Query Poisoning URL Interpretation attacks Input Validation attacks Extend SQL statements

  12. Firewalls cannot prevent… Reverse-engineering HTTP cookies. Web Client Web Server Web app DB Web app DB Web app Web app • HTTP session hijacking. • Impersonation. URL Interpretation attacks Input Validation attacks SQL query poisoning

  13. The URL as a cruise missile http: // 10.0.0.1 / catalogue / display.asp ? pg = 1 & product = 7 Web Server Web app DB Web app DB Web app Web app

  14. Web Hacks - net effects Web Hacks cause three types of effects: • Extra information disclosure. (paths, etc.) • Source code and arbitrary file content disclosure. • Extra data disclosure (e.g. return all rows) • Arbitrary command execution.

  15. The Web Hacker’s Toolbox Some desired accessories would be … • a port scanner, • netcat, • vulnerability checker (e.g. whisker), • OpenSSL, … etc.

  16. Hacking over SSL • Some SSL Myths: • “We are secure because we use SSL!” • “Strong 128 bit crypto being used” • “We use Digital Certificates signed by VeriSign”

  17. Hacking over SSL • Using netcat and OpenSSL, it is possible to create a simple two-line SSL Proxy! • Listen on port 80 on a host and redirect requests to port 443 on a remote host through SSL. SSL web server web client nc openssl

  18. Use the Source, Luke • Source code disclosure may reveal any flaws in the application design. • Can be used to retrieve application configuraiton files. • e.g. global.asa, etc.

  19. Source Code Disclosure • WebLogic / Tomcat example:

  20. Source code disclosure • IIS +.htr example:

  21. SQL Query Poisoning • Poor input validation on parameters passed to SQL queries can be disastrous. • For example: Dim sql_con, result, sql_qry Const CONNECT_STRING = "Provider=SQLOLEDB;SERVER=WEB_DB;UID=sa; PWD=xyzzy" sql_qry = "SELECT * FROM PRODUCT WHERE ID = “ & Request.QueryString(“ID”) Set objCon = Server.CreateObject("ADODB.Connection") objCon.Open CONNECT_STRING Set objRS = objCon.Execute(strSQL)

  22. SQL Query Poisoning • Return all rows: http://10.0.0.3/showtable.asp? ID=3+OR+1=1 • Resultant query: SELECT * FROM PRODUCT WHERE ID=3 OR 1=1

  23. SQL Query Poisoning • Drop Table: http://10.0.0.3/showtable.asp? ID=3%01DROP+TABLE+PRODUCT • Resultant query: SELECT * FROM PRODUCT WHERE ID=3 DROP TABLE PRODUCT

  24. SQL Query Poisoning • Remote Command Execution! http://10.0.0.3/showtable.asp? ID=3%01EXEC+master..xp_cmdshell+ ‘copy+\winnt\system32\cmd.exe+ \inetpub\scripts’ • Command executed: copy \winnt\system32\cmd.exe \inetpub\scripts

  25. One-way attacks • Assume the tightest firewall configuration. • All legal HTTP requests. • No outbound traffic from internal network. • …yet, total control. • Illustrates how the smallest of openings can be big enough to drive a truck through it!

  26. One-way attacks … entry point • One entry point required. • Arbitrary command execution. • Can be achieved in many ways: • Known vulnerability (e.g. IIS Unicode / ddecode) • Buffer overflow (sometimes kills server!) • Fooling the application itself! (metacharacters, SQL query poisoning)

  27. One-way attacks … uploader • Create an HTTP multipart-MIME upload mechanism. • The same process as sending attachments over web-based mail (yahoo, hotmail). • Uploader allows the attacker to plant and execute tools on the server. • The hole widens.

  28. One-way attacks … remote prompt • Install a remote web-based command prompt. • HTML form, passes inputs to the command-shell on the server. • Semi-interactive.

  29. One-way attacks … SQL prompts! • A step further, install a SQL query prompt page! • Allows attackers to arbitrarily pick and attack back-end SQL servers. • Web programming languages such as ASP, PHP allow back-end database interfaces. • Pilfering of database credentials from source code disclosure attacks would be useful!

  30. One-way attacks … getting root! • Upload your favourite privilege escalation $pl01t! • Run it through the web-based command prompt. • Get admin/root privileges!

  31. One-way attacks … going further • Drive through the back-end network. • Portscanning • Service enumeration • Network packet sniffing • Recovering passwords / credentials • … it’s all open now!

  32. WinDump • Loads dynamically – don’t have to reboot box. • Works great with MDAC, Unicode, etc… • Sniff internal networks after attack. • Grep for user/pass – Pipe output. • Send results back through nc. • Send results back through firewall as an HTML page – ultra cool because it bypasses firewall

  33. Root Causes of Web Hacks • Complex web architectures may cause oversight in web server configuration. • URL Parsing. • File Canonicalization. • Combination of underlying operating system and web server may leave holes.

  34. Root Causes of Web Hacks • Untested code used in web applications, to save time. • Level of security consciousness low in web application developers. • Security vs. convenience. • Security vs. time-to-market. • Zero knowledge administration breeds zero knowledge administrators.

  35. Web Security Measures • Heighten security awareness amongst administrators, developers and most important - TOP MANAGEMENT! • Firewalls and SSL do not solve all security problems. • Keep abreast of latest vendor advisories and patches. • Monitor security mailing lists such as BugTraq. :-/

  36. Thank You! jd.glaser@foundstone.com saumil.shah@foundstone.com

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