Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
An adversary embeds malicious script code in the parameters of an HTTP query string and convinces a victim to submit the HTTP request that contains the query string to a
Common Attack Pattern Enumeration and Classification
A Community Resource for Identifying and Understanding Attacks
An adversary embeds malicious script code in the parameters of an HTTP query string and convinces a victim to submit the HTTP request that contains the query string to a vulnerable web application. The web application then procedes to use the values parameters without properly validation them first and generates the HTML code that will be executed by the victim's browser.
Web applications that accept name value pairs in a HTTP Query string are inherently at risk to any value (or name for that matter) that an attacker would like to enter in the query string. This can be done manually via web browser or trivially scripted to post the query string to multiple sites. In the latter case, in the instance of many sites using similar infrastructure with predictable http queries being accepted and operated on (such as blogging software, Google applications, and so on), a single malicious payload can be scripted to target a wide variety of sites.
Web 2.0 type sites like Technorati and del.icio.us rely on user generated content like tags to build http links that are displayed to other users. del.icio.us allows users to identify sites, tag them with metadata and provide URL, descriptions and more data. This data is then echoed back to any other web browser that is interested in the link. If the data is not validated by the del.icio.us site properly then an arbitrary code can be added into the standard http string sent to del.icio.us by the attacker, for example formatted as normal content with a URL and description and tagged as Java, and available to be clicked on (and executed by) any user browsing for Java content that clicks on this trojaned content.
Skill or Knowledge Level: Low
To place malicious payload on server via HTTP
Skill or Knowledge Level: High
Exploiting any information gathered by HTTP Query on script host
Design: Use browser technologies that do not allow client side scripting.
Design: Utilize strict type, character, and encoding enforcement
Design: Server side developers should not proxy content via XHR or other means, if a http proxy for remote content is setup on the server side, the client's browser has no way of discerning where the data is originating from.
Implementation: Ensure all content that is delivered to client is sanitized against an acceptable content specification.
Implementation: Perform input validation for all remote content, including remote and user-generated content
Implementation: Perform output validation for all remote content.
Implementation: Session tokens for specific host
Implementation: Patching software. There are many attack vectors for XSS on the client side and the server side. Many vulnerabilities are fixed in service packs for browser, web servers, and plug in technologies, staying current on patch release that deal with XSS countermeasures mitigates this.
Implementation: Privileges are constrained, if a script is loaded, ensure system runs in chroot jail or other limited authority mode
Script delivered through standard web server, such as a web server with user-generated content.
Client web browser may be used to steal session data, passwords, cookies, and other tokens.
[R.32.1] [REF-2] G. Hoglund and G. McGraw. "Exploiting Software: How to Break Code". Addison-Wesley. February 2004.
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