XSS (Cross-site Scripting) allows an attacker to execute a dynamic script (Javascript, VbScript) in the context of the application. This allows several different attack opportunities, mostly hijacking the current session of the user or changing the look of the page by changing the HTML on the fly to steal the user's credentials. This happens because the input entered by a user has been interpreted as HTML/Javascript/VbScript by the browser.
XSS targets the users of the application instead of the server. Although this is a limitation, since it allows attackers to hijack other users' session, an attacker might attack an administrator to gain full control over the application.
Impact
There are many different attacks that can be leveraged through the use of XSS, including:
Hi-jacking users' active session
Changing the look of the page within the victims browser.
Mounting a successful phishing attack.
Intercept data and perform man-in-the-middle attacks.
Remedy
The issue occurs because the browser interprets the input as active HTML, Javascript or VbScript. To avoid this, all input and output from the application should be filtered. Output should be filtered according to the output format and location. Typically the output location is HTML. Where the output is HTML ensure that all active content is removed prior to its presentation to the server.
Prior to sanitizing user input, ensure you have a pre-defined list of both expected and acceptable characters with which you populate a white-list. This list needs only be defined once and should be used to sanitize and validate all subsequent input.
There are a number of pre-defined, well structured white-list libraries available for many different environments, good examples of these include, OWASP Reform and Microsoft Anti Cross-site Scripting libraries are good examples.
Netsparker identified that the target web server is an Apache server. This was disclosed through the HTTP response. This information can help an attacker to gain a greater understanding of the systems in use and potentially develop further attacks targeted at the specific version of Apache.
Impact
An attacker can search for specific security vulnerabilities for the version of Apache identified within the SERVER header.
Remedy
Configure your web server to prevent information leakage from the SERVER header of its HTTP response.
Netsparker identified that the target web server is disclosing the PHP version in use through the HTTP response. This information can help an attacker to gain a greater understanding of the systems in use and potentially develop further attacks targeted at the specific version of PHP.
Impact
An attacker can look for specific security vulnerabilities for the version identified. Also the attacker can use this information in conjunction with the other vulnerabilities in the application or the web server.
Netsparker identified that the target web server is disclosing OpenSSL version in the HTTP response. This information can help an attacker to develop further attacks and also the system can become an easier target for automated attacks.
Impact
An attacker can look for specific security vulnerabilities for the identified version. Also the attacker can use this information in conjunction with the other vulnerabilities in the application or the web server.
Remedy
Configure your web server to prevent information leakage from the SERVER header of its HTTP response.
Netsparker identified that the target web server is disclosing one of the Apache modules version. This was disclosed through the HTTP response. This information can help an attacker to gain a greater understanding of the systems in use and potentially develop further attacks targeted at the specific version of Apache.
Impact
An attacker can look for specific security vulnerabilities for the identified Apache module version. The attacker can also use this information in conjunction with the other vulnerabilities in the application or the web server.
Remedy
Configure your web server to prevent information leakage from the SERVER header of its HTTP response.
