8.2

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-47423

CVE-2026-47423: DOMPurify XSS via selectedcontent re-clone

Summary

DOMPurify 3.4.4 allows selectedcontent by default, allowing a chain in which browsers "re-clone" an XSS payload after sanitization, effectively bypassing DOMPurify.

Details

The chain is as follows:

The browser parses the input and creates a <selectedcontent> clone from the selected <option>
DOMPurify walks and sanitizes that generated clone.
DOMPurify reaches the original <option> and removes selected=javascript:1
The browser refreshes the <selectedcontent> clone from the original option's content.
The refreshed clone is in a subtree DOMPurify already walked, which DOMPurify doesn't go back to sanitize
The returned string contains unsanitized markup inside <selectedcontent>.

PoC

const dirty =
  '<select><button><selectedcontent></selectedcontent></button>' +
  '<option selected=javascript:1>' +
  '<img src=x onerror=alert(1)>x' +
  '</option></select>';

const clean = DOMPurify.sanitize(dirty);
console.log(clean);

document.body.innerHTML = clean;

Observed "sanitized" output in Chromium 148/WebKit 625:

<select><button><selectedcontent><img src="x" onerror="alert(1)">x</selectedcontent></button><option><img src="x">x</option></select>

After reinsertion, the browser updates the live DOM and strips the handler from the displayed clone, but the onerror has already fired:

<select><button><selectedcontent><img src="x">x</selectedcontent></button><option><img src="x">x</option></select>

Reproduced in Chromium and WebKit, but not Safari (not yet latest WebKit) or Firefox. Will likely change with browser support for selectedcontent.

Impact

This is a default-configuration DOMPurify sanitizer bypass resulting in XSS.

Applications are impacted if they sanitize attacker-controlled HTML with DOMPurify 3.4.4 using the string-input path and then insert the returned string into the page, for example with innerHTML.

(GitHub Advisory)

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CVE-2026-47423

CVE-2026-47423:

8.2

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
dompurify	npm	= 3.4.4	3.4.5

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability in DOMPurify 3.4.4 is a cross-site scripting (XSS) bypass caused by the default allowance of the <selectedcontent> HTML tag. The exploit chain relies on a specific browser behavior where content is re-cloned into a <selectedcontent> element after DOMPurify has already performed its sanitization pass. An attacker can craft HTML with a malicious payload inside an <option> tag. When DOMPurify sanitizes the input, it processes the <selectedcontent> element first. Then, it moves to the <option> tag and removes malicious attributes. However, some browsers will then refresh the <selectedcontent> element based on the original (pre-sanitization) content of the <option> tag. Since DOMPurify does not re-sanitize this element, the malicious payload is restored and executed. The fix, implemented in version 3.4.5, is to remove <selectedcontent> from the list of allowed tags, thus preventing this exploit chain from the beginning. The primary function involved in this process is DOMPurify.sanitize, which is the main entry point for the library's sanitization capabilities.

Vulnerable functions

DOMPurify.sanitize

src/purify.ts

The `DOMPurify.sanitize` function is the entry point for the sanitization process. In the vulnerable version, this function allowed the 'selectedcontent' tag by default. This could be exploited in certain browsers where the browser would re-clone content into the 'selectedcontent' element after DOMPurify had already sanitized it, leading to an XSS vulnerability. The function itself is not flawed, but its behavior with the default configuration (allowed tags) is what creates the vulnerability. The patch fixes this by removing 'selectedcontent' from the default set of allowed tags.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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