Published Oct 28, 2026Sources checked Oct 29, 2026
5.9MEDIUMCVSS out of 10
What this means
Review the available evidence
CVE-2026-118370 and is rated Medium severity with a CVSS score of 5.9. 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 29, 2026
Release Notes
CISA KEVNot listedBased on the latest collected catalog
EPSS0.4%Estimated 30-day exploitation probability
Ransomware useNot markedCISA KEV ransomware field
Threat actors0Source-linked actor relationships
Overview
What is CVE-2026-118370?
libexpat through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.