CVE-2026-65902 in DOMPurify
Summary
by MITRE • 07/23/2026
DOMPurify before 3.4.7 (affected versions <= 3.4.5) passes direct references to the module-level DEFAULT_ALLOWED_TAGS and DEFAULT_ALLOWED_ATTR sets to the uponSanitizeElement and uponSanitizeAttribute hooks via data.allowedTags / data.allowedAttributes when sanitize is called without an explicit cfg.ALLOWED_TAGS / cfg.ALLOWED_ATTR array. A hook that mutates these fields permanently widens the default allow-lists for the lifetime of the DOMPurify instance, so all subsequent default-config sanitize calls inherit the widened defaults and attacker payloads using the poisoned tag/attribute name survive sanitization. removeAllHooks(), clearConfig(), and passing a fresh cfg do not recover the state; only constructing a new DOMPurify instance does.
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Analysis
by VulDB Data Team • 07/23/2026
This vulnerability resides in the DOMPurify library version 3.4.5 and earlier, where the sanitization process suffers from a critical flaw in how it handles default allow-list configurations within its hook system. The core issue manifests when the sanitize function operates without explicit configuration parameters for allowed tags and attributes, causing the library to directly reference module-level DEFAULT_ALLOWED_TAGS and DEFAULT_ALLOWED_ATTR sets. These references are then passed through to uponSanitizeElement and uponSanitizeAttribute hooks via data.allowedTags and data.allowedAttributes properties, creating a direct pathway for malicious manipulation.
The technical exploitation occurs when a hook function modifies these shared default allow-lists during execution, permanently expanding the scope of what elements and attributes are considered safe. This mutation affects all subsequent sanitization operations performed by the same DOMPurify instance, as the modified allow-lists persist throughout the instance's lifetime. Attackers can leverage this vulnerability by crafting payloads that utilize tag or attribute names that were previously added to the default allow-list through malicious hook execution, allowing these elements to bypass sanitization checks and potentially execute XSS attacks or other malicious code.
The operational impact of this vulnerability extends beyond simple bypassing of security controls, as it fundamentally undermines the trust model of DOMPurify's configuration management. Even standard recovery mechanisms such as removeAllHooks(), clearConfig(), and passing fresh configuration objects fail to restore the original state of the allow-lists because the modifications persist at the module level rather than being confined to individual sanitize calls. This persistence means that applications using DOMPurify in a multi-request or long-running context become increasingly vulnerable over time, as each malicious hook execution compounds the damage by permanently expanding the attack surface.
The vulnerability aligns with CWE-862, which addresses insufficient authorization, and represents a form of configuration pollution where legitimate system components are manipulated to weaken security boundaries. From an ATT&CK perspective, this maps to T1548.005 (Server Software Component Compromise) and T1071.004 (Application Layer Protocol: DNS) as it enables attackers to manipulate core sanitization functionality and potentially bypass network-level protections. The flaw demonstrates poor encapsulation principles in the library's design, where internal state management fails to properly isolate mutable configuration elements from external hook execution contexts.
Mitigation strategies require immediate upgrading to DOMPurify version 3.4.7 or later, which addresses this vulnerability by ensuring that hooks receive immutable copies of the allow-lists rather than direct references. Organizations should also implement comprehensive monitoring for any hook-based configurations in their applications and consider implementing additional validation layers beyond basic sanitization. The recommended approach involves either explicitly defining ALLOWED_TAGS and ALLOWED_ATTR configuration parameters to prevent reliance on default behavior, or ensuring that all hook execution contexts are properly sandboxed and validated before allowing modifications to core security parameters.