CVE intelligence

CVE-2026-56403

Vulnerability intelligence

Published Jun 21, 2026Sources checked Nov 10, 2026

6.9MEDIUMCVSS out of 10

What this means

Review the available evidence

CVE-2026-56403 and is rated Medium severity with a CVSS score of 6.9. It is not in the current CISA KEV record we collected. That does not prove exploitation has not occurred.

What to do next

Remediation and response

Microsoft Security Response Center guidance

Vendor revision: Oct 22, 2026

CBL-Mariner Releases

Vendor-listed releases

2.8.2-1

CISA KEVNot listedBased on the latest collected catalog

EPSS0.2%Estimated 30-day exploitation probability

Ransomware useNot markedCISA KEV ransomware field

Threat actors0Source-linked actor relationships

Overview

What is CVE-2026-56403?

libexpat before 2.8.2 has an integer overflow in storeAtts.

Source: NVD