CVE-2026-124493: SunEditor before 3.4.0 Stored XSS via DocumentType Header textContent

Published Nov 8, 2026

Updated

SunEditor before 3.4.0 contains a stored cross-site scripting vulnerability in the DocumentType constructor that injects header textContent into innerHTML without HTML escaping. Attackers can store entity-encoded HTML in h1-h6 headers that executes JavaScript when editors using document:header mode initialize, enabling session cookie theft.

Remediation

Recommended actions to resolve this vulnerability, in priority order.

Upgrade
Upgrade SunEditor to a version that resolves this vulnerability.
Fixed in 3.4.0

Event History

Nov 8, 2026

CVE Published

via MITRE·01:16 PM

Data Sourced

via MITRE·01:16 PM

DescriptionWeakness

Data Sourced

via NVD·02:18 PM

DescriptionSeverityWeakness

Frequently Asked Questions

Which deployments are exposed to this issue?

SunEditor versions before 3.4.0 are affected when they use document:header mode. The stored payload executes when an editor using that mode initializes.

What does an attacker need to do to exploit it?

An attacker needs a way to store entity-encoded HTML in an h1 through h6 header. When the affected editor later initializes in document:header mode, the header content is inserted into innerHTML without HTML escaping and can execute JavaScript.

How can I determine whether stored content may already be dangerous?

Review h1-h6 header content stored through SunEditor for entity-encoded HTML, particularly in environments using document:header mode. Such content may execute when an affected editor instance initializes.

CVE-2026-124493: SunEditor before 3.4.0 Stored XSS via DocumentType Header textContent

Remediation

Event History

Frequently Asked Questions

Which deployments are exposed to this issue?

What does an attacker need to do to exploit it?

How can I determine whether stored content may already be dangerous?

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Resources

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Frequently Asked Questions

Which deployments are exposed to this issue?

What does an attacker need to do to exploit it?

How can I determine whether stored content may already be dangerous?