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Common WebApp Vulnerabilities and What to Do About Them


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With more and more services becoming internet-facing, web application security is now a problem for most of us. In response to this, the OWASP security community have been working for years to catalogue, understand and prioritise common web application vulnerabilities, published as the “OWASP Top 10 List”.

In this session, Eoin will review the OWASP Top 10 list to understand the vulnerabilities and dig into the implementation details of some of the more important of them to identify practical mitigations for them in our own applications.

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Common WebApp Vulnerabilities and What to Do About Them

  1. 1. QUALITY. PRODUCTIVITY. INNOVATION. Common Web Security Threats … and what to do about them Eoin Woods Endava
  2. 2. 3 3 Introductions Eoin Woods • CTO at Endava • Career has spanned products and applications • Architecture and software engineering • Bull, Sybase, InterTrust • BGI (Barclays) and UBS • Long time security dabbler • Increasingly concerned at cyber threat for “normal” systems
  3. 3. 4 4 Content Introducing Web Security Threats The OWASP Web Vulnerabilities List Useful Tools to Know About Reviewing Defences Summary
  4. 4. Introducing Web Security Threats
  5. 5. 6 6 Web Security Threats We need systems that are dependable in the face of • Malice • Error • Mischance People are sometimes bad, stupid or just unlucky System security aims to mitigate these situations
  6. 6. 7 7 Web Security Threats System threats are similar to real-world threats: • Theft • Fraud • Destruction • Disruption Anything of value may attract unwelcome attention “I rob banks because that’s where the money is” – Willie Sutton
  7. 7. 8 8 Web Security Threats Why do we care about these threats? • A threat is a risk of a loss of some sort Common types of loss are: • Time • Money • Privacy • Reputation • Advantage
  8. 8. 9 Web Security Threats Security today mitigates tomorrow’s threat Digital channels demand web security • System interfaces on the Internet • Introspection of APIs • Attacks being “weaponised” • Today’s internal app is tomorrow’s “digital channel”
  9. 9. 10 10 Who are OWASP? The Open Web Application Security Project • Largely volunteer organisation, largely online Exists to improve the state of software security • Research, tools, guidance, standards • Runs local chapters for face to face meetings (UK has 10+) “OWASP Top 10” project lists top application security risks • Referenced widely by MITRE, PCI DSS and similar • Updated every few years (2003, 2004, 2007, 2010, 2013)
  10. 10. 11 11 Other Selected Security Organisations MITRE Corporation • Common Vulnerabilities and Exposures (CVE) • Common Weaknesses Enumeration (CWE) SAFECode • Fundamental Practices for Secure Software Development • Training There are a lot of others too (CPNI, CERT, CIS, ISSA, …)
  11. 11. OWASP Web Vulnerabilities List
  12. 12. 13 13 OWASP Top 10 - 2013 #1 Injection Attacks #2 Authentication and Session Management #3 Cross Site Scripting (XSS) #4 Direct Object Reference #5 Security Misconfiguration #6 Sensitive Data Exposure #7 Function Level Access Control #8 Cross Site Request Forgery (CSRF) #9 Component Vulnerabilities #10 Unvalidated Redirects and Forwards These may look “obvious” but appear on the list year after year, based on real vulnerability databases!
  13. 13. 14 14 #1 Injection Attacks Unvalidated input passed to an interpreter • Operating system and SQL are most common Defences include “escaping” inputs, bind variables, using white lists, … SELECT * from table1 where name = ’%1’ Set ‘%1’ to ‘ OR 1=1 -- … this results in this query: SELECT * FROM table1 WHERE name = ’ ’ OR 1=1 --
  14. 14. 15 15 #2 Broken Authentication or Session Management • HTTP is stateless - some sort of credential sent every time • Credential on non-TLS connection can be tampered with • Session ID often displayed but can be used as login details • Defences are strong authentication and session management controls a5f3dd56ff32 a5f3dd56ee33
  15. 15. 16 16 #3 Cross Site Scripting • Occurs when script is injected into a user’s web page • Reflected attack – crafted link in email … • Persistent attack - database records, site postings, activity listings • Allows redirection, session data stealing, page corruption, … • Defences include validation and escaping on the server-side
  16. 16. 17 17 #4 Insecure Direct Object Refs Directly referencing filenames, IDs and similar in requests • Not authenticating access to each on the server • e.g. relying on limited list of options returned to client • Client can modify request and gain access to other objects Defences include using pseudo references on client and authenticating all object accesses … how about: ??
  17. 17. 18 18 #5 Security Misconfiguration Security configuration is often complicated • Many different places to put it, complex semantics • Layers from OS to application all need to be consistent It is easy to accidentally miss an important part • OS file permissions? • .htaccess files? • Shared credentials in test and production? Allows accidental access to resources or even site modification Mitigation via scanning, standardisation, simplicity and automation
  18. 18. 19 19 #6 Sensitive Data Exposure Is sensitive data secured in transit? • TLS, message encryption Is sensitive data secured at rest? • Encryption, tokenisation, separation Risks include loss of data or spoofing attacks Mitigation via threat analysis, limiting scope, standardisation
  19. 19. 20 20 #7 Function Level Access Control Relying on information sent to the client for access control • e.g. page menu omitting “update” and “delete” option for a record • Not checking the action (function) being performed on the server Client can guess the right request form for the other actions • Bypassed security model - also see #4 Insecure Object References Never trust the client - check authorisation for every request à
  20. 20. 21 21 #8 Cross Site Request Forgery User triggers malicious code that submits fraudulent request using browser security context • e.g. click a link => run JavaScript => change Github password Various subtle variations on this make defence quite difficult • How you do you know it is the user? Primary defence is the “challenge value” in pages • Check for the latest challenge value in requests • Add authentication steps for sensitive operations • Keep short sessions with real logout process
  21. 21. 22 22 #9 Known Vulnerable Components Source:
  22. 22. 23 23 #9 Known Vulnerable Components Many commonly used components have vulnerabilities • See weekly US-CERT list for a frightening reality check! • Much OSS doesn’t have well researched vulnerabilities Few teams consider security of their 3rd party components • And keeping everything up to date is disruptive Consider automated scanning of 3rd party components, actively review vulnerability lists, keep components patched
  23. 23. 24 24 #10 Unvalidated Redirects and Forwards Redirecting or forwarding to targets based on parameters Avoid using parameters for redirect or forward targets Where parameter is needed use a key and map on server -> http://…/selectpage? (Without careful validation this redirects user to malicious page)
  24. 24. 25 25 Summary of Attack Vector Types Interpreter injections • Operating System, SQL, … Page injections • HTML, XSS (JavaScript) Lack of Validation • trusting client side restrictions • allowing session IDs and cookies to be reused, • not checking input fields thoroughly • parameter values directly in pages and links Missing data protection • data loss, spoofing, man in the middle, … Platform • configuration mistakes, vulnerabilities, complexity
  25. 25. Useful Tools
  26. 26. 27 • Deliberately insecure LAMP web application • So run in a VM! • Provides examples of the OWASP Top 10 in action • Use it to explore and understand them Mutillidae
  27. 27. 28 • Commercial proxy, scanning, pentest tool • Very capable free version available • Inspect traffic, manipulate headers and content, … • Made in Knutsford! BurpSuite
  28. 28. 29 • Chrome and SwitchySharp or other similar pairing • Allows easy switching of proxy server to BurpSuite Browser and Proxy Switcher
  29. 29. 30 • Automated SQL injection and database pentest tool • Open source Python based command line tool • Frighteningly effective! SQLMap
  30. 30. 31 • Commercial tool suite with online database • Scans build pipelines for component security vulnerabilities • Alerts and dashboards for monitoring Sonatype Component Lifecycle Manager
  31. 31. 32 32 BlackDuck Hub • Commercial tool and database for open source security, audit & compliance • Scans build pipelines looking for open source with known vulnerabilities • Alerts and dashboards for monitoring
  32. 32. Demonstrations
  33. 33. 34 34 Mutillidae Mutillidae BurpSuite (proxy)Browser with proxy plugin
  34. 34. 35 35 An Example Multi-Step Attack - Impersonation Attacks rarely use just one vulnerability 1. SQL Injection User list obtained Persistent XSS achieved XSS Script executed 4. Steal browser state Sessions etc. saved
  35. 35. Reviewing Defences
  36. 36. 37 37 Key Web Vulnerability Defences Don’t trust clients (browsers) • Validation, authorisation, … Identify “interpreters”, escape inputs, use bind variables, … • Command lines, web pages, database queries, … Protect valuable information at rest and in transit • Use encryption judiciously Simplicity • Verify configuration and correctness Standardise and Automate • Force consistency, avoid configuration errors
  37. 37. 38 38 Don’t Trust Clients Be wary when trusting anything from a browser • You don’t control it • Sophisticated code execution (& injection) platform • Output can be manipulated Assume or prevent tampering • TLS connections to avoid 3rd party interception • Short lived sessions • Reauthenticate regularly & before sensitive operations • Consider multi-factor authentication • Use opaque tokens not real object references for params • Validate everything
  38. 38. 39 39 Watch out for injection Many pieces of software act as interpreters • Browser for HTML and JavaScript • Operating system shells – system(“mv $1 $2”) • Databases – query languages • Configuration files Assume that someone will work it out! • Avoid creating commands using string manipulation • Use libraries and bind variables • Escape all strings being passed to an “interpreter” • Use a third party “escaping” library (e.g. OWASP) • Reject excessively long strings (e.g. username > 30 char)
  39. 39. 40 40 Protect Valuable Information Defence in depth – assume perimeter breach • Encrypt messaging as standard • Consider database encryption • Consider file or filesystem encryption However encryption complicates using the data • Slows everything down • Can you query while encrypted? • Message routing on sensitive fields (in headers) • How do you manage and rotate the keys? • What about restore on disaster recovery?
  40. 40. 41 41 Simplicity & Standardisation Complexity is the enemy of security • “You can’t secure what you don’t understand” - Schneier • Special cases will be forgotten Simplify, Standardise and Automate • Simpler things are easier to check and secure • Standardising an approach means there are no special cases to forget to handle • Automation eliminates human inconsistencies from the process so avoiding a type of risk
  41. 41. Summary
  42. 42. 43 43 Summary Much of the technology we use is inherently insecure • Mitigation needs to be part of application development Attacking systems is becoming industrialised • Digital transformation is providing more valuable, insecure targets Fundamental attack vectors appear again and again • Injection, interception, page manipulation, validation, configuration, … Most real attacks exploit a series of vulnerabilities • Each vulnerability may not look serious, the combination is Most mitigations not difficult but need to be applied consistently • … and may conflict with other desirable qualities
  43. 43. 44 44 Books
  44. 44. 45 Thank you QUALITY. PRODUCTIVITY. INNOVATION. Eoin Woods CTO +44 207 367 1000 en_ewoods