CVE-2026-56411: xmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarations.

mediumCVSS 6.9CVE-2026-56411

CSIRTS triage

vendor: libexpat product: libexpatOtheraffected: before 2.8.2

What: This vulnerability is an integer overflow in endDoctypeDecl via NOTATION declarations.
Who is affected: Users of libexpat versions before 2.8.2 are affected.
Urgency: Remediation is important due to a medium severity rating.
Action: Upgrade to libexpat version 2.8.2 or later.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 6.9
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-56411

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-564110.11% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 2% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-56411	coverage & exploitation status	NVD · CVE.org

Recent advisories for xmlwf in libexpat

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-56409: xmlwf in libexpat before 2.8.2 has an integer overflow for the output filename when -d outputD…msrc · 2026-06-09
mediumCVE-2026-56410: xmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId.msrc · 2026-06-09