An adversary inserts commands to perform cross-site scripting (XSS) actions in HTML attributes. Many filters do not adequately sanitize attributes against the presence of potentially dangerous commands even if they adequately sanitize tags. For example, dangerous expressions could be inserted into a style attribute in an anchor tag, resulting in the execution of malicious code when the resulting page is rendered. If a victim is tricked into viewing the rendered page the attack proceeds like a normal XSS attack, possibly resulting in the loss of sensitive cookies or other malicious activities.

How does a XSS Targeting HTML Attributes attack work?

It typically unfolds over 4 phases. It begins with: [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.

How do you prevent CAPEC-243?

Design: Use libraries and templates that minimize unfiltered input.

What weaknesses does CAPEC-243 target?

CAPEC-243 exploits 1 CWE weakness, including CWE-83 (Improper Neutralization of Script in Attributes in a Web Page).

How severe is CAPEC-243?

MITRE rates CAPEC-243 as Medium severity.

CAPEC-243: XSS Targeting HTML Attributes

How the attack works

The phases an attacker typically follows to carry out this attack.

Step 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.
- Use a spidering tool to follow and record all links and analyze the web pages to find entry points. Make special note of any links that include parameters in the URL.
- Use a proxy tool to record all links visited during a manual traversal of the web application.
- Use a browser to manually explore the website and analyze how it is constructed. Many browsers' plugins are available to facilitate the analysis or automate the discovery.
Step 2
Experiment
[Probe identified potential entry points for XSS targeting HTML attributes] The adversary uses the entry points gathered in the "Explore" phase as a target list and injects various malicious expressions as input, hoping to embed them as HTML attributes.
- Inject single and double quotes into URL parameters or other inputs to see if they are filtered out. Also use URL encoding to bypass filters.
- Use single or double quotes to close attribute evaluation and enter a new attribute that contains an expression.
Step 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.
- Execute a script using an expression embedded in an HTML attribute, which avoids needing to inject a script tag.
- Send information gathered from the malicious script to a remote endpoint.
Step 4
Exploit
[Get victim to click URL] In order for the attack to be successful, the victim needs to access the malicious URL.
- Send a phishing email to the victim containing the malicious URL. This can be hidden in a hyperlink as to not show the full URL, which might draw suspicion.
- Put the malicious URL on a public forum, where many victims might accidentally click the link.

CAPEC-243: XSS Targeting HTML Attributes

Overview

How the attack works

What the attacker needs

Prerequisites

Resources required

How to mitigate it

Frequently asked questions

What is CAPEC-243?

How does a XSS Targeting HTML Attributes attack work?

How do you prevent CAPEC-243?

What weaknesses does CAPEC-243 target?

How severe is CAPEC-243?

References

Defend against CAPEC-243

Overview

How the attack works

What the attacker needs

Prerequisites

Resources required

How to mitigate it

Related weaknesses

Related attack patterns

Parent

Frequently asked questions

What is CAPEC-243?

How does a XSS Targeting HTML Attributes attack work?

How do you prevent CAPEC-243?

What weaknesses does CAPEC-243 target?

How severe is CAPEC-243?

References

Defend against CAPEC-243