How severe is CVE-2026-49978?

No CVSS score has been assigned to CVE-2026-49978 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-49978?

CVE-2026-49978 affects the following packages: dompurify (npm). Ecosystems affected: npm.

How do I fix CVE-2026-49978?

Update dompurify to 3.4.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49978 is resolved across your whole dependency graph.

How do I detect CVE-2026-49978 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompurify, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-49978 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2026-49978 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-49978 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-49978?

CVE-2026-49978 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 34th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-49978?

CVE-2026-49978 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-49978 published, and has it been updated?

CVE-2026-49978 was published on July 14, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2026-49978: dompurify XSS

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-49978.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs34th percentile — riskier than 34% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

6Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

dompurifynpm

45.3Mdownloads / week

Description

If the HTML you give it contains a <template> element, and inside that template there's an element with a shadow DOM attached to it, DOMPurify quietly skips over the shadow contents. Whatever the attacker put in there - an image with an onerror handler, a link with a javascript: URL, even a full script - survives untouched. The moment the application uses that template the way templates are meant to be used (cloning it and inserting the result into the page), the malicious payload comes along and runs as if it had never been sanitized. From there an attacker gets everything XSS normally gets them: session cookies, stored tokens, the ability to act as the user, and the ability to leave persistent payloads behind for the next person who visits.

advisory.pdf

poc.html

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`dompurify`	all versions	3.4.7`npm install dompurify@3.4.7`

Affected Products

1 product · 1 configurations

Application

dompurifycure53

< 3.4.7

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompurify, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update dompurify to 3.4.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49978 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This vulnerability in DOMPurify is rated as Important as it allows for cross-site scripting (XSS) attacks. When DOMPurify performs in-place sanitization, it may fail to properly process shadow DOM content within `<template>.content`, enabling an attacker to embed and execute malicious JavaScript. This could lead to…

Product	Fixed in	Advisory
Cryostat 4 on RHEL 9	`cryostat/cryostat-openshift-console-plugin-rhel9:4.2.0-14`	RHSA-2026:68333
Red Hat AMQ Broker 7.13.6	`dompurify`	RHSA-2026:66545
Red Hat AMQ Broker 7.14.1	`dompurify`	RHSA-2026:66488
Red Hat build of Apicurio Registry 3.3.1	`apicurio/apicurio-registry-ui-rhel8`	RHSA-2026:59360
Red Hat Data Grid 8.6.3	`dompurify`	RHSA-2026:69296
Red Hat Enterprise Linux 10	`rh-podman-desktop-0:1.1.2-1.el10_2`	RHSA-2026:57590
Streams for Apache Kafka 3.2.1	`dompurify`	RHSA-2026:54435
Red Hat Advanced Cluster Security 4.9	`advanced-cluster-security/rhacs-main-rhel8:1785413210`	RHSA-2026:48872

Frequently Asked Questions

If the HTML you give it contains a <template> element, and inside that template there's an element with a shadow DOM attached to it, DOMPurify quietly skips over the shadow contents. Whatever the attacker put in there - an image with an onerror handler, a link with a javascript: URL, even a full script - survives untouched. The moment the application uses that template the way templates are meant to be used (cloning it and inserting the result into the page), the malicious payload comes along and runs as if it had never been sanitized. From there an attacker gets everything XSS normally gets t

O3 Security · Impact-Aware SCA

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CVE-2026-49978 — dompurify