| Name |
XSS Targeting HTML Attributes |
|
| Likelyhood of attack |
Typical severity |
| High |
Medium |
|
| Summary |
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. |
| Prerequisites |
The target application must fail to adequately sanitize HTML attributes against the presence of dangerous commands. |
| Execution Flow |
| Step |
Phase |
Description |
Techniques |
| 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.
|
| 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.
|
| 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.
|
| 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.
|
|
| Solutions | Design: Use libraries and templates that minimize unfiltered input. Implementation: Normalize, filter and use an allowlist for all input including that which is not expected to have any scripting content. Implementation: The victim should configure the browser to minimize active content from untrusted sources. |
| Related Weaknesses |
|
CWE ID
|
Description
|
| CWE-83 |
Improper Neutralization of Script in Attributes in a Web Page |
|
| Related CAPECS |
|
CAPEC ID
|
Description
|
| CAPEC-588 |
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. |
| CAPEC-591 |
This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is "reflected" off a vulnerable web application and then executed by a victim's browser. The process starts with an adversary delivering a malicious script to a victim and convincing the victim to send the script to the vulnerable web application. |
| CAPEC-592 |
This type of attack is a form of Cross-site Scripting (XSS) where a malicious script is persistenly "stored" within the data storage of a vulnerable web application. Initially presented by an adversary to the vulnerable web application, the malicious script is incorrectly considered valid input and is not properly encoded by the web application. A victim is then convinced to use the web application in a way that creates a response that includes the malicious script. This response is subsequently sent to the victim and the malicious script is executed by the victim's browser. To launch a successful Stored XSS attack, an adversary looks for places where stored input data is used in the generation of a response. This often involves elements that are not expected to host scripts such as image tags (<img>), or the addition of event attibutes such as onload and onmouseover. These elements are often not subject to the same input validation, output encoding, and other content filtering and checking routines. |
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