DOMPurify could allow a remote attacker to execute arbitrary code on the system, caused by a prototype pollution flaw in depth check. By adding or modifying properties of Object.prototype using a proto or constructor payload, an attacker could exploit this vulnerability to execute arbitrary code or cause a denial of service condition on the system.

DOMPurify 3.0.0 before 3.4.9 does not reset the retained Trusted Types policy when clearConfig() is called, so a DOMPurify instance reused across trust boundaries stays bound to a previously supplied TRUSTEDTYPESPOLICY. A later caller that requests RETURNTRUSTEDTYPE output receives a TrustedHTML object created by the old (potentially unsafe) policy rather than a clean default, which can lead to script execution at a Trusted Types sink. Passing TRUSTEDTYPESPOLICY: null on the later call also does not clear the retained policy.

DOMPurify versions >=3.0.0 and before 3.4.8, when configured with SAFEFORTEMPLATES together with a DOM output mode (RETURNDOM, RETURNDOMFRAGMENT, or INPLACE), fail to strip template expressions (e.g. ${evil}, {{evil}}, <%evil%>) inside <template> element content. The final normalization/scrub pass (scrubTemplateExpressions) uses a NodeIterator and node.normalize() that do not descend into template.content, so expressions that only form after adjacent text nodes merge survive sanitization. This bypasses SAFEFORTEMPLATES and can allow a downstream template engine to evaluate attacker-supplied expressions. The string output path is not affected.

DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG. DOMpurify was vulnerable to nesting-based mXSS. This vulnerability is fixed in 2.5.0 and 3.1.3.