CVE-2026-56404: libexpat before 2.8.2 has an integer overflow in addBinding.

mediumCVSS 6.9CVE-2026-56404

CSIRTS triage

vendor: libexpat product: libexpatOtheraffected: before 2.8.2

What: An integer overflow vulnerability exists in libexpat's addBinding function.
Who is affected: Deployments of libexpat before version 2.8.2 are affected by this vulnerability.
Urgency: Remediation is medium priority due to the CVSS score of 6.9 indicating moderate risk.
Action: Upgrade libexpat to version 2.8.2 or later to mitigate this vulnerability.

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-2026-56404

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-2026-564040.10% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 1% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-56404	coverage & exploitation status	NVD · CVE.org

Recent advisories for 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.

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mediumCVE-2026-56131: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from wit…msrc · 2026-06-09
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