Top 5 Most Common Web Application Vulnerabilities

A Web application vulnerability is a system bug that could be exploited for some kind of harmful purposes. It's main task is to compromise the security of an application. It plays a major role in the Computer security part. Once the attacker has discovered a flaw or a vulnerability, he tries to gain access by exploiting it and thus performs a cyber crime. These crimes are done for accessing the confidential data of companies, its users, creation, etc. The hackers use typical methods and specific tools to find the vulnerability and exploit it. The most common types of Vulnerabilities include:
 

1. Cross Site Scripting (XSS) - Cross site scripting is a type of attack in which an attacker injects malicious codes into the websites. An attacker can use XSS to send a malicious script to an unsuspecting user. The end user’s browser has no way to know that the script should not be trusted, and will execute the script. Because it thinks the script came from a trusted source, the malicious script can access any cookies, session tokens, or other sensitive information retained by your browser and used with that site. These scripts can even rewrite the content of the HTML page. The following script can be inserted anywhere in the search field of website.
2. SQL Injection (SQLi) - A SQL injection attack consists of insertion or "injection" of a SQL query via the input data from the client to the application. A successful SQL injection exploit can read sensitive data from the database, modify database data (Insert/Update/Delete), execute administration operations on the database (such as shutdown the DBMS), recover the content of a given file present on the DBMS file system and in some cases issue commands to the operating system. SQL injection attacks are a type of injection attack, in which SQL commands are injected into data-plane input in order to effect the execution of predefined SQL commands. 
3.  Cross Site Request Forgery (CSRF) - CSRF is an attack which forces an end user to execute unwanted actions on a web application in which he/she is currently authenticated. With a little help of social engineering (like sending a link via email/chat), an attacker may force the users of a web application to execute actions of the attacker's choosing. A successful CSRF exploit can compromise end user data and operation in case of normal user. If the targeted end user is the administrator account, this can compromise the entire web application. 
4.  Broken Authentication & Session Management -
   Authentication and session management includes all aspects of handling user authentication and managing active sessions. Authentication is a critical aspect of this process, but even solid authentication mechanisms can be undermined by flawed credential management functions, including password change, forgot my password, remember my password, account update, and other related functions. Because “walk by” attacks are likely for many web applications, all account management functions should require re-authentication even if the user has a valid session id.
   User authentication on the web typically involves the use of a user id and password. Stronger methods of authentication are commercially available such as software and hardware based cryptographic tokens or biometrics, but such mechanisms are cost prohibitive for most web applications. A wide array of account and session management flaws can result in the compromise of user or system administration accounts.
5. Security Misconfiguration - This is one of those vulnerabilities which makes it a bit hard to pinpoint. Security Misconfiguration can range from the currency of frameworks, to the settings in the Web.config, to the access rights of database accounts. It based on how configurable settings within the app are handled – not code. If your app uses a web server, a framework, an app platform, a database, a network or contains any code, you are at risk of security misconfiguration. So, to put into perspective, that would be all of us.

           *Information Source: OWASP