However, IFrames are still very effective for pulling off phishing attacks. Cross-site Scripting vulnerabilities are one of the most common web application vulnerabilities. Take a demo and find out more about running XSS scans against your website or web application. To keep yourself safe from XSS, you must sanitize your input. Your application code should never output data received as input directly to the browser without checking it for malicious code.
Specific prevention techniques depend on the subtype of XSS vulnerability, on user input usage context, and on the programming framework.
However, there are certain general strategic principles that you should follow to keep your web application safe. To keep your web application safe, everyone involved in building the web application must be aware of the risks associated with XSS vulnerabilities.
You can start by referring them to this page. In such cases, use a trusted and verified library to parse and clean HTML. Choose the library depending on your development language, for example, HtmlSanitizer for. If you do, such cookies will not be accessible via client-side JavaScript. CSP is an HTTP response header that lets you declare the dynamic resources that are allowed to load depending on the request source.
You should regularly scan your web applications using a web vulnerability scanner such as Acunetix. If you use Jenkins, you should install the Acunetix plugin to automatically scan every build.
Frequently asked questions How does Cross-site Scripting work? Note that about one in three websites is vulnerable to Cross-site scripting. Learn more about the current state of web security. For example, an attacker may use it to steal user credentials and log in to your website as that user.
If that user is an administrator, the attacker gains control over your website. See an example of a dangerous XSS attack from the past.
To discover Cross-site Scripting, you may either perform manual penetration testing or first use a vulnerability scanner. If you use a vulnerability scanner, it will save you a lot of time and money because your penetration testers can then focus on more challenging vulnerabilities. Here is a simple example of a reflected XSS vulnerability:. The application doesn't perform any other processing of the data, so an attacker can easily construct an attack like this:.
If the user visits the URL constructed by the attacker, then the attacker's script executes in the user's browser, in the context of that user's session with the application. At that point, the script can carry out any action, and retrieve any data, to which the user has access.
Stored XSS also known as persistent or second-order XSS arises when an application receives data from an untrusted source and includes that data within its later HTTP responses in an unsafe way. The data in question might be submitted to the application via HTTP requests; for example, comments on a blog post, user nicknames in a chat room, or contact details on a customer order. In other cases, the data might arrive from other untrusted sources; for example, a webmail application displaying messages received over SMTP, a marketing application displaying social media posts, or a network monitoring application displaying packet data from network traffic.
Here is a simple example of a stored XSS vulnerability. A message board application lets users submit messages, which are displayed to other users:. The application doesn't perform any other processing of the data, so an attacker can easily send a message that attacks other users:. In the following example, an application uses some JavaScript to read the value from an input field and write that value to an element within the HTML:.
If the attacker can control the value of the input field, they can easily construct a malicious value that causes their own script to execute:.
An attacker who exploits a cross-site scripting vulnerability is typically able to:. The actual impact of an XSS attack generally depends on the nature of the application, its functionality and data, and the status of the compromised user.
For example:. The vast majority of XSS vulnerabilities can be found quickly and reliably using Burp Suite's web vulnerability scanner. Manually testing for reflected and stored XSS normally involves submitting some simple unique input such as a short alphanumeric string into every entry point in the application, identifying every location where the submitted input is returned in HTTP responses, and testing each location individually to determine whether suitably crafted input can be used to execute arbitrary JavaScript.
In this way, you can determine the context in which the XSS occurs and select a suitable payload to exploit it. Manually testing for DOM-based XSS arising from URL parameters involves a similar process: placing some simple unique input in the parameter, using the browser's developer tools to search the DOM for this input, and testing each location to determine whether it is exploitable. Burp Suite's web vulnerability scanner combines static and dynamic analysis of JavaScript to reliably automate the detection of DOM-based vulnerabilities.
Content security policy CSP is a browser mechanism that aims to mitigate the impact of cross-site scripting and some other vulnerabilities. Often, the CSP can be circumvented to enable exploitation of the underlying vulnerability. This increases the reach of the attack, endangering all visitors no matter their level of vigilance. A web application firewall WAF is the most commonly used solution for protection from XSS and web application attacks.
WAFs employ different methods to counter attack vectors. In the case of XSS, most will rely on signature based filtering to identify and block malicious requests. Imperva cloud WAF is offered as a managed service, regularly maintained by a team of security experts who are constantly updating the security rule set with signatures of newly discovered attack vectors.
Imperva crowdsourcing technology automatically collects and aggregates attack data from across its network, for the benefit of all customers. The crowdsourcing approach enables extremely rapid response to zero-day threats, protecting the entire user community against any new threat, as soon as a single attack attempt is identified.
Crowdsourcing also enables the use of IP reputation system that blocks repeated offenders, including botnet resources which tend to be re-used by multiple perpetrators. Cross site scripting XSS attacks What is cross site scripting XSS Cross site scripting XSS is a common attack vector that injects malicious code into a vulnerable web application.
Cross site scripting attacks can be broken down into two types: stored and reflected. What is stored cross site scripting To successfully execute a stored XSS attack, a perpetrator has to locate a vulnerability in a web application and then inject malicious script into its server e.
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