.NET Security Topics
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This document discusses various security topics for .NET applications including cross-site scripting (XSS), SQL injection, cross-site request forgery (CSRF), clickjacking, and secure file handling. It provides definitions, examples, and mitigation strategies for each topic. Code examples are shown for XSS defenses, SQL injection defenses, CSRF defenses, clickjacking defenses, and secure file uploads. The document also includes additional tips and resources for developing secure .NET applications.
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.NET Security Topics
- 1. .NETSecurityTopics XSS, SQL Injection, CSRF, ClickJacking, Secure File Handling, Odds & Ends for .NET
- 2. Cross-site Scripting (XSS) Definitions Examples Mitigation strategies Mitigation examples
- 3. Definitions Cross-site Scripting (XSS) Occurs when a web application gathers malicious data from a user (untrusted source).The data is usually gathered in the form of a hyperlink or form submission, database, or cookie which contains malicious content within it. Malicious data is generally in the form of Javascript or HTML Types are DOM-based, “stored” (persistent) and “reflected” (non- persistent)
- 4. Examples Cross-site Scripting (XSS) http://en.wikipedia.org/wiki/Cross_site_scripting#Exploit_scenarios <SCRIPT type="text/javascript"> var adr = '../evil.php?cakemonster=' + escape(document.cookie); </SCRIPT> <body onload=alert('test1')> <b onmouseover=alert('Wufff!')>click me!</b> <img src="http://url.to.file.which/not.exist" onerror=alert(document.cookie);> <IMG SRC=jAvascript:alert('test2')> <META HTTP-EQUIV="refresh" CONTENT="0;url=data:text/html;base64,PHNjcml wdD5hbGVydCgndGVzdDMnKTwvc2NyaXB0Pg">
- 5. Mitigations Cross-site Scripting (XSS) Explicitly set character set encoding (meta charset) Identify special characters Encode all dynamic output (htmleditformat) Filter special characters in dynamic elements (blacklist – not preferable) Stronger data validation (whitelist/positive – preferable) Never count on client side validation (it can be turned off) Use HttpOnly cookies Use secure cookies whenever possible No one thing will mitigate all threats, it will require use of multiple techniques
- 6. XSS Defense Code Show the code
- 7. SQL Injection Definitions Examples Mitigation strategies Mitigation examples
- 8. Definitions SQL Injection (fromWikipedia) Technique often used to attack data driven applications by including portions of SQL statements in an entry field in an attempt to get the website to pass a newly formed rogue SQL command to the database (e.g., dump the database contents to the attacker). The vulnerability happens when user input is either incorrectly filtered for string literal escape characters embedded in SQL statements or user input is not strongly typed and unexpectedly executed. SQL injection is mostly known as an attack vector for websites but can be used to attack any type of SQL database. In operational environments, it has been noted that applications experience an average of 71 attempts an hour
- 9. Examples SQL Injection http://en.wikipedia.org/wiki/SQL_injection#Examples http://www.mydomain.com/products/products.asp?productid=123 or 1=1 http://www.mydomain.com/products/products.asp?productid=123; DROP TABLE Products
- 10. Mitigations SQL Injection Never trust input data.Validate everything Avoid dynamic SQL built with string concatenation Prefer stored procedures 0r ORM If dynamic SQL, used parameterized commands Sensitive/confidential data should be encrypted Limit connection privilege (no DBO or SA)
- 11. SQL Injection Defense Examples Show the code snips
- 12. Cross-site Request Forgery (CSRF) Definition Examples Mitigation strategies
- 13. Definition Cross-site Request Forgery (CSRF) Attack which forces an end user to execute unwanted actions on a web application in which he/she is currently authenticated. Embed HTML in malicious site that preys on users authenticated on other sites. Submitting unauthorized data to your application from other servers (untrusted) Not easy to make a successful attack, but that doesn’t mean we shouldn’t protect ourselves
- 14. Examples Cross-site Request Forgery (CSRF) <img src="http://bank.example/withdraw?account=bob&amount=1000000&for=ma llory"> Million-dollar dream home example
- 15. Mitigation General mitigation strategy Per request tokens (nonce) to url/form Referrer checking (less desirable – spoofing)
- 16. OtherGeneralPrinciplesThatApply Good practices Log detected exploit attempts and notify someone Lock out attacker Be careful about exposing error data, it can be extremely helpful to an attacker
- 17. CSRF Defense Show the code
- 18. ClickJacking OWASP Definition: Clickjacking, also known as a "UI redress attack", is when an attacker uses multiple transparent or opaque layers to trick a user into clicking on a button or link on another page when they were intending to click on the the top level page.Thus, the attacker is "hijacking" clicks meant for their page and routing them to other another page, most likely owned by another application, domain, or both. Using a similar technique, keystrokes can also be hijacked.With a carefully crafted combination of stylesheets, iframes, and text boxes, a user can be led to believe they are typing in the password to their email or bank account, but are instead typing into an invisible frame controlled by the attacker.
- 19. Examples For example, imagine an attacker who builds a web site that has a button on it that says "click here for a free iPod". However, on top of that web page, the attacker has loaded an iframe with your mail account, and lined up exactly the "delete all messages" button directly on top of the "free iPod" button.The victim tries to click on the "free iPod" button but instead actually clicked on the invisible "delete all messages" button. In essence, the attacker has "hijacked" the user's click, hence the name "Clickjacking". One of the most notorious examples of Clickjacking was an attack against the Adobe Flash plugin settings page. By loading this page into an invisible iframe, an attacker could trick a user into altering the security settings of Flash, giving permission for any Flash animation to utilize the computer's microphone and camera. Clickjacking also made the news in the form of aTwitter worm.This clickjacking attack convinced users to click on a button which caused them to re-tweet the location of the malicious page, and propagated massively. Recently, clickjacking attacks abusing Facebook's "Like" functionality has grown significantly. Attackers can trick logged-in Facebook users to arbitrarily like fan pages, links, groups, etc
- 21. Defenses – Coding against Javascript code to make sure current frame is the top level window (Ok, but not great, not going to show it) Browser response headers (Good, and will get better)
- 22. Response Headers X-FRAME-OPTIONS Response header that newer browsers recognize, which controls framing behavior https://www.owasp.org/index.php/Clickjacking#Defending_with_ response_headers Be sure to read the limitations, specifically the stuff about proxies, and know that not all options are currently supported (ALLOW- FROM only IE8+). Code example (ASP.NET).
- 23. ClickJacking Resources https://www.owasp.org/index.php/Clickjacking http://en.wikipedia.org/wiki/Clickjacking http://nakedsecurity.sophos.com/2010/05/31/viral-clickjacking- like-worm-hits-facebook-users/ http://ha.ckers.org/blog/20081007/clickjacking-details/ http://blogs.msdn.com/b/sdl/archive/2009/02/05/clickjacking- defense-in-ie8.aspx http://blogs.msdn.com/b/ieinternals/archive/2010/03/30/combatin g-clickjacking-with-x-frame-options.aspx http://www.enhanceie.com/test/clickjack/
- 24. ClickJacking Defense Show the code
- 25. Secure File Upload Principles Whitelist what you accept Validate file format and other attributes Upload to safe location outside the webroot
- 26. Image Resizing Show the code
- 27. Odds & Ends - Tips Be careful in what you include in error messages that get thrown to a browser Sanitize log input (don’t XSS your log database) Cigital SecureAssist plugin forVS. Visual Studio Code Analysis (general code quality issues)
- 28. Resources OWASP http://www.owasp.org/index.php/Cross-site_scripting http://www.owasp.org/index.php/Top_10_2007-A1 http://www.owasp.org/index.php/SQL_Injection http://www.owasp.org/index.php/CSRF CERT http://www.cert.org/tech_tips/malicious_code_mitigation.html Wikipedia http://en.wikipedia.org/wiki/Cross_site_scripting http://en.wikipedia.org/wiki/SQL_injection http://en.wikipedia.org/wiki/Cross-site_request_forgery XSS Cheat Sheet http://ha.ckers.org/xss.html http://blog.stevensanderson.com/2008/09/01/prevent-cross-site- request-forgery-csrf-using-aspnet-mvcs-antiforgerytoken- helper/ http://msdn.microsoft.com/en-us/magazine/hh708755.aspx http://weblogs.asp.net/scottgu/archive/2010/04/06/new-lt-gt- syntax-for-html-encoding-output-in-asp-net-4-and-asp-net- mvc-2.aspx
- 29. Resources http://cheesewz.tumblr.com/post/87099308919/springpad-is-dead https://docs.google.com/spreadsheets/d/1CV4bQDpaGbXUSHdn WwQUxzsu4fVdn2vzBWO72Y3Hk1s/edit?usp=sharing http://html5sec.org/ http://blogs.microsoft.co.il/blogs/sasha/archive/2013/05/06/attacki ng-web-applications.aspx https://www.sans.org/course/secure-coding-net-developing- defensible-applications http://www.pluralsight.com/training/Courses
Editor's Notes
- I group these two topics because most of the mitigation actions are the same, though the threat itself is different.
- DOM-based rely on locally stored web pages. Stored attacks are stored in the database and retrieved in output to users. Reflected attacks are where the injected code is reflected off of the webserver, and usually delivered in an email (Phishing) or off of another server.
- Talk about the cheat sheet. Talk about the one from the PEN test. Examples may seem silly, but if you can popup an alert it can be a very deep rabbit hole
- <META http-equiv="Content-Type" content="text/html; charset=IS O-8859-1"> <META http-equiv="Content-Type" content="text/html; UTF-8">
- I group these two topics because most of the mitigation actions are the same, though the threat itself is different.
- DOM-based rely on locally stored web pages. Stored attacks are stored in the database and retrieved in output to users. Reflected attacks are where the injected code is reflected off of the webserver, and usually delivered in an email (Phishing) or off of another server.
- Talk about the cheat sheet. Talk about the one from the PEN test. Examples may seem silly, but if you can popup an alert it can be a very deep rabbit hole
- <META http-equiv="Content-Type" content="text/html; charset=IS O-8859-1"> <META http-equiv="Content-Type" content="text/html; UTF-8">
- XSS Cheat Sheet has tons of sample exploit code to test mitigations against.