CVE-2026-56132: In libexpat before 2.8.2, there is a heap-based buffer overflow in doProlog in xmlparse.c because scaffold backing array reallocation is mishandled when there is data-structure sharing across parsers.

mediumCVSS 6.9CVE-2026-56132

CSIRTS triage

vendor: libexpat product: libexpat Memory corruptionaffected: before 2.8.2

What: A heap-based buffer overflow vulnerability exists in libexpat due to mishandling of reallocation.
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-2026-56132

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-2026-561320.11% 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-2026-56132	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

medium[UPDATE] [medium] expat: Multiple vulnerabilitiescert-bund

Recent advisories for 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-2026-56406: libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check tha…msrc · 2026-06-09
mediumCVE-2026-56405: libexpat before 2.8.2 has an integer overflow in getAttributeId.msrc · 2026-06-09
mediumCVE-2026-56411: xmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarat…msrc · 2026-06-09
mediumCVE-2026-56131: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from wit…msrc · 2026-06-09
mediumCVE-2026-50219: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_GetBuffer, XML_Parse,…msrc · 2026-06-09