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

Status: published. Published: 2026-11-08. Updated: 2026-11-12.

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

No remediation reported in collected sources

## Affected products and versions

- JiHong88 / suneditor: ≥ 0; < 3.4.0 (affected, semver); 3.4.0 (unaffected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 9.3 (critical); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N; source: CNA: VulnCheck

- CVSS 4.0: 9.3 (critical); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: 0.34% as of 2026-11-12; percentile 28.35%

- SSVC: exploitation poc; automatable yes; technical impact total; source ADP: CISA-ADP

- Weaknesses: CWE-79

## Exploit evidence

- exploit: https://github.com/JiHong88/suneditor/security/advisories/GHSA-h9pq-57qf-vvfh (ADP: CISA-ADP)

## References

- https://github.com/JiHong88/suneditor/security/advisories/GHSA-h9pq-57qf-vvfh (CNA: VulnCheck; vendor-advisory)

- https://www.vulncheck.com/advisories/suneditor-before-3.4.0-stored-xss-via-documenttype-header-textcontent (CNA: VulnCheck; third-party-advisory)

- https://github.com/JiHong88/suneditor/security/advisories/GHSA-h9pq-57qf-vvfh (ADP: CISA-ADP; exploit)

- https://github.com/JiHong88/suneditor/security/advisories/GHSA-h9pq-57qf-vvfh (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/suneditor-before-3.4.0-stored-xss-via-documenttype-header-textcontent (disclosure@vulncheck.com)

- https://github.com/JiHong88/suneditor/security/advisories/GHSA-h9pq-57qf-vvfh (134c704f-9b21-4f2e-91b3-4a467353bcc0)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-124493; retrieved 2026-11-12; source updated 2026-11-12

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-124493; retrieved 2026-11-13; source updated 2026-11-12

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-124493; retrieved 2026-11-12; source updated Not reported

Revision: cda8056675fc22bbf652f97b2194836cab6f0b6fda98b3da6d3c9fb3372b0c99

Canonical: https://y2.dev/cve/CVE-2026-124493

## Agent and API access

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- Public catalog: https://y2.dev/cve/index.json. Follow nextCursor with the same search, filters, sort, and limit (1–100). A null cursor marks the end.

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- Cyber API: https://api.y2.dev/api/v2/cyber/cves and https://api.y2.dev/api/v2/cyber/cves/{cveId}.

- Y2 Pro or Elite: create a workspace API key with the intel:cyber scope and send Authorization: Bearer <Y2_API_KEY>. Setup: https://y2.dev/docs/api/create-key.

- x402: Pay per request without an account or API key. Omit Authorization, read the HTTP 402 PAYMENT-REQUIRED challenge, validate its current requirements, and retry with PAYMENT-SIGNATURE through an authorized payment client. These browser tools never make payments. Guide: https://y2.dev/docs/api/x402.

- OpenAPI: https://y2.dev/api/openapi.yaml. Agent access metadata: https://y2.dev/cve/agent.json.

Collected public records only. Check source status for coverage and freshness.