Full Report
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Analysis Summary
# Vulnerability: DOM-based Cross-Site Scripting (XSS) in Web Applications
## CVE Details
- **CVE ID**: Not specifically assigned (Refers to a class of vulnerability addressed by a new browser feature)
- **CVSS Score**: N/A (General vulnerability class)
- **CWE**: CWE-79 (Improper Neutralization of Input During Web Page Generation), specifically CWE-1021
## Affected Systems
- **Products**: Any web application utilizing the Document Object Model (DOM) to dynamically render user-controlled content.
- **Versions**: Applications using legacy methods like `innerHTML` for content injection.
- **Configurations**: Client-side scripts that parse data from the URL, `localStorage`, or other client-side sources and write it to the page without sanitization.
## Vulnerability Description
DOM-based XSS occurs when an application contains client-side JavaScript that processes data from an untrusted source in an unsafe way, usually by writing the data back to the DOM. Unlike reflected or stored XSS, the payload is never sent to the server; it is executed entirely within the victim's browser. The use of the `innerHTML` property is a primary sink for these attacks as it renders any HTML tags (including `<script>`) contained within the assigned string.
## Exploitation
- **Status**: Exploited in the wild (General class of attack)
- **Complexity**: Low to Medium
- **Attack Vector**: Network (via malicious links or hijacked third-party scripts)
## Impact
- **Confidentiality**: High (Access to session cookies, local storage, and user data)
- **Integrity**: High (Ability to modify page content or perform actions on behalf of the user)
- **Availability**: Low (Can be used to deface or redirect the site)
## Remediation
### Patches
- **Browser-level Mitigation**: Upgrade to **Firefox 148+**. This version introduces the **Sanitizer API**, which allows developers to use `setHTML()` instead of `innerHTML`. The API automatically strips malicious elements and attributes.
- **Application-level Fix**: Developers should migrate from `element.innerHTML = data;` to `element.setHTML(data);`.
### Workarounds
- Use `textContent` instead of `innerHTML` when no HTML rendering is required.
- Implement a robust Content Security Policy (CSP) to restrict script execution sources.
- Use trusted client-side sanitization libraries (e.g., DOMPurify) for older browsers.
## Detection
- **Indicators of Compromise**: Presence of unexpected `<script>` tags or `onerror` attributes in the DOM; unusual network requests to unknown domains originating from the client.
- **Detection methods and tools**:
- Use Static Application Security Testing (SAST) to find `innerHTML` sinks.
- Use Dynamic Application Security Testing (DAST) or browser-based debuggers to inspect DOM mutations at runtime.
## References
- **Mozilla Developer Advisory**: hxxps[://]hacks[.]mozilla[.]org/2026/02/goodbye-innerhtml-hello-sethtml-stronger-xss-protection-in-firefox-148/
- **UK Government VMS Announcement**: hxxps[://]www[.]gov[.]uk/government/news/government-cuts-cyber-attack-fix-times-by-84-and-launches-new-profession-to-protect-public-services