Tag: DDoS

Most common attacks of web servers and web applications

Posted on by Admin@itgoodtoknow
  • Cross-Site Scripting (“XSS“)
    • Hackers can inject JavaScript into a web page
    • Used to steal cookies a session data
    • Often very successful just because browser trusts JavaScript
      • Protection:
        • Sanitize any dynamic context that gets output to browser (HTML, JavaScript, JSON, XML…)
        • Pay special attention to data that come directly from URLs or forms
        • Be careful about database data, cookies, session data
        • Use Whitelists to allow certain HTML tags and sanitize everything else
    • Cross-Site Request Forgery (CSRF)
      • Hackers tricks user into making a request to your server
      • Used for fraudulent clicks
      • Forging login request
        • Protection
          • Accept POST request only
          • Use a “form token” in user’s section
          • Add a hidden field to forms with form token as value
          • Compare session form token and submitted form token
          • Store the token generation time in user’s session
    • SQL Injection
      • Hacker is able to execute arbitrary SQL request in order to probe database schema, steal data(usernames, passwords, credit cards, encrypted data), assign elevated privileges, truncate or drop tables
        • Protection
          • Use limited privileges to application’s database user
          • Sanitize input
          • Escape for SQL using libraries
          • Use prepared statements
    • URL manipulation
      • Editing the URL string to probe the site
      • Can be used for revealing private information, performing restricted actions
        • Protection
      • Remember that URLs are exposed and easily editable
      • Implement proper access control
      • Keep error messages vague
      • Clarify your GET and POST requests, only POST requests should be used for making changes
    • Cookie Stealing
      • Cookie data is visible to users
      • Cookies can be stolen using XSS attack
      • Remember that cookies can be sniffed by observing network traffic by using packet analyzers (most popular Wireshark)
        • Protection
          • Put only non sensitive data in cookies
          • Use HttpOnly cookies
        • Use HTTPs cookies
        • Set cookie expiration date
        • Set cookie domain, sub domain and path
        • Encrypt cookie data
        • User server side sessions instead of client side cookies
    • Session hijacking
      • Stealing session ID is similar to stealing cookie but much more valuable
      • Can be used to steal personal info, passwords
      • Often done by network sniffing
      • Never use open wireless networks at coffee shops for transmitting sensitive data
      • Variation of session hijacking is session fixation
      • Session fixation is opposite to session hijacking, it trick a user into a hacker provided session identifier
        • Protection
          • Use SSL
          • Save user agent in session and confirm it (not ideal method)
          • Check IP address of a computer who is making a request (not ideal as well)
          • Use HttpOnly cookies
          • Regenerate session ID periodically, at key points, especially important to regenerate after log in
          • Expire and remove old session files regularly and keep track of last activity in session
        • Do not accept session identifier from from GET or POST variables, session identifier should come from only one place – cookies
    • Remote system execution attack

      • It’s the most dangerous attack when hacker remotely run operating system commands on a web server
        • Protection
          • Avoid system execution keywords (they are language specific)
          • Perform system execution with extra caution
          • Sanitize any dynamic data carefully
          • Understand system commands and their syntax
          • Add additional data validation
    • File upload abuse
      • Can be used to upload too much data (quantity, file size)
      • Can be used to upload warm or virus
        • Protection
          • Require user authentication, no anonymous uploads
          • Limit maximum upload size
          • Limit allowable file formats, file extensions
          • Use caution when opening uploaded file
          • Do not host uploaded files which have not been verified
    • Denial of Service (DoS) attack

      • Attempt to make a server unavailable to users
      • Usually performed by overloading a server with requests
      • Includes DNS and routing disruption
      • If performed by distributed network pf computers it called DDoS
        • Protection
          • Properly configure firewalls, IDS, switches, load balancers and routers
        • Collection of reverse proxies
        • Map you infrastructure
        • Keep infrastructure up to date
        • Make network traffic visible
        • Develop DRP plan
        • Consider changing IP address
        • “Black hole” or “null route” traffic