CAPEC-588 DOM-Based XSS

This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is inserted into the client-side HTML being parsed by a web browser. Content served by a vulnerable web application includes script code used to manipulate the Document Object Model (DOM). This script code either does not properly validate input, or does not perform proper output encoding, thus creating an opportunity for an adversary to inject a malicious script launch a XSS attack. A key distinction between other XSS attacks and DOM-based attacks is that in other XSS attacks, the malicious script runs when the vulnerable web page is initially loaded, while a DOM-based attack executes sometime after the page loads. Another distinction of DOM-based attacks is that in some cases, the malicious script is never sent to the vulnerable web server at all. An attack like this is guaranteed to bypass any server-side filtering attempts to protect users.

1. [Explore] [Survey the application for user-controllable inputs] Using a browser or an automated tool, an adversary follows all public links and actions on a web site. They record all the links, the forms, the resources accessed and all other potential entry-points for the web application. 2. [Experiment] [Probe identified potential entry points for DOM-based XSS vulnerability] The adversary uses the entry points gathered in the "Explore" phase as a target list and injects various common script payloads and special characters to determine if an entry point actually represents a vulnerability and to characterize the extent to which the vulnerability can be exploited. Specific to DOM-based XSS, the adversary is looking for areas where input is being used to directly change the DOM. 3. [Experiment] [Craft malicious XSS URL] Once the adversary has determined which parameters are vulnerable to XSS, they will craft a malicious URL containing the XSS exploit. The adversary can have many goals, from stealing session IDs, cookies, credentials, and page content from the victim. In DOM-based XSS, the malicious script might not even be sent to the server, since the victim's browser will manipulate the DOM itself. This can help avoid serve-side detection mechanisms. 4. [Exploit] [Get victim to click URL] In order for the attack to be successful, the victim needs to access the malicious URL.

• An application that leverages a client-side web browser with scripting enabled. • An application that manipulates the DOM via client-side scripting. • An application that failS to adequately sanitize or encode untrusted input.

• [Medium] Requires the ability to write scripts of some complexity and to inject it through user controlled fields in the system.

• Confidentiality: Read Data • Confidentiality, Authorization, Access Control: Gain Privileges • Confidentiality, Integrity, Availability: Execute Unauthorized Commands • Integrity: Modify Data

• Use browser technologies that do not allow client-side scripting. • Utilize proper character encoding for all output produced within client-site scripts manipulating the DOM. • Ensure that all user-supplied input is validated before use.