CVE-2026-65914 in DOMPurify
Summary
by MITRE • 07/23/2026
DOMPurify before 3.3.2 contains a mutation-XSS vulnerability when sanitized HTML is reinserted into special parsing contexts using innerHTML with wrappers like script, xmp, iframe, noembed, noframes, or noscript. Attackers can craft payloads with closing sequences that break out of the wrapper context during reparsing, reactivating dangerous markup with event handlers to execute JavaScript.
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Analysis
by VulDB Data Team • 07/23/2026
DOMPurify versions prior to 3.3.2 contain a critical mutation-cross-site scripting vulnerability that arises from improper handling of HTML sanitization within specific parsing contexts. This flaw occurs when sanitized HTML content is subsequently reinserted into the DOM using innerHTML methods, particularly when wrapped within special HTML elements such as script, xmp, iframe, noembed, noframes, or noscript. The vulnerability stems from the browser's re-parsing behavior where these wrapper elements create distinct parsing contexts that are not properly accounted for during the sanitization process. When malicious payloads are crafted with specific closing sequences, they can break out of the intended wrapper context during the reparsing phase, effectively neutralizing the sanitization measures that were previously applied.
The technical implementation of this vulnerability leverages the inherent characteristics of HTML parsing and re-parsing mechanisms within web browsers. During the initial sanitization process, DOMPurify removes or escapes potentially dangerous markup elements and attributes. However, when the sanitized content is later inserted back into the DOM using innerHTML within special wrapper contexts, the browser's parser encounters these elements differently than during the original sanitization phase. The mutation-XSS occurs because the re-parsing process can interpret certain sequences as valid HTML markup rather than text content, allowing previously sanitized dangerous elements to be reactivated with their event handlers intact.
The operational impact of this vulnerability extends beyond typical XSS scenarios and represents a sophisticated attack vector that can bypass security controls designed to prevent cross-site scripting. Attackers can craft payloads that exploit the specific timing and context of re-parsing operations to execute JavaScript code in the victim's browser session. This vulnerability is particularly concerning because it operates at the intersection of HTML sanitization and DOM manipulation, creating a scenario where security measures intended to protect against XSS can actually be subverted by the very mechanisms they rely upon for protection. The attack requires careful crafting of payloads that take advantage of the specific parsing behaviors of different wrapper elements and their interaction with the browser's HTML parser during re-parsing operations.
This vulnerability aligns with CWE-116, which addresses improper encoding or escaping of output, and represents a variant of mutation-based XSS attacks that exploit differences in parsing behavior between sanitization and execution contexts. The attack pattern corresponds to techniques documented in the ATT&CK framework under T1203, specifically targeting web application security controls through manipulation of HTML parsing and re-parsing behaviors. Organizations relying on DOMPurify for HTML sanitization must understand that this vulnerability can compromise the effectiveness of their security measures, potentially allowing attackers to execute arbitrary JavaScript code within user sessions. The recommended mitigation strategy involves upgrading to DOMPurify version 3.3.2 or later, which includes fixes specifically addressing the mutation-XSS vulnerability in special parsing contexts. Additionally, administrators should consider implementing additional security controls such as Content Security Policy headers and regular security audits of HTML sanitization implementations to prevent exploitation of similar vulnerabilities in other libraries or custom implementations.