[UPDATE] [medium] libexpat: Multiple vulnerabilities allow unspecified attack

CSIRTS triage

What

A local attacker can exploit multiple vulnerabilities in libexpat to conduct an unspecified attack, potentially including arbitrary code execution, data manipulation, bypassing security measures, disclosing confidential information, or causing a Denial of Service condition.

Who is affected

Users of libexpat.

Urgency

Remediation is medium urgency due to the wide range of potential impacts.

Action

Update to the latest version of libexpat to mitigate these vulnerabilities.

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

Details

Source

CERT-Bund (BSI) Security Advisories (DE · national-cert · site)

Severity

medium

Published

2026-07-22

Exploitation

Not in CISA KEV at last sync

Language

Machine-translated to English — verify against the original

Original advisory: https://wid.cert-bund.de/portal/wid/securityadvisory?name=WID-SEC-2026-2025

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-2026-502190.29% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 21% of all scored CVEs.
• Low exploitation riskCVE-2026-564030.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564040.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564050.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564060.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564070.12% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564080.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564090.13% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all scored CVEs.
• Low exploitation riskCVE-2026-564100.14% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 4% of all scored CVEs.
• Low exploitation riskCVE-2026-564110.14% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 4% of all scored CVEs.

Referenced CVEs

Same CVEs, other sources

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

• unknownDSA-6404-1 expat - security updatedebian
• mediumCVE-2026-56405: libexpat before 2.8.2 has an integer overflow in getAttributeId.msrc
• mediumCVE-2026-56411: xmlwf in libexpat before 2.8.2 has an integer overflow in endDoctypeDecl via NOTATION declarat…msrc
• mediumCVE-2026-56407: libexpat before 2.8.2 has an integer overflow in doProlog that is related to storeEntityValue …msrc
• mediumCVE-2026-56410: xmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId.msrc
• mediumCVE-2026-56404: libexpat before 2.8.2 has an integer overflow in addBinding.msrc
• mediumCVE-2026-56403: libexpat before 2.8.2 has an integer overflow in storeAtts.msrc
• mediumCVE-2026-56412: libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks ha…msrc
• mediumCVE-2026-50219: libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_GetBuffer, XML_Parse,…msrc
• mediumCVE-2026-56406: libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check tha…msrc
• mediumCVE-2026-56409: xmlwf in libexpat before 2.8.2 has an integer overflow for the output filename when -d outputD…msrc

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.

• low[UPDATE] [low] libexpat: Multiple vulnerabilities allow denial of servicecert-bund · 2026-07-24
• 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-2026-56407: libexpat before 2.8.2 has an integer overflow in doProlog that is related to storeEntityValue …msrc · 2026-06-09
• mediumCVE-2026-56410: xmlwf in libexpat before 2.8.2 has an integer overflow in resolveSystemId.msrc · 2026-06-09
• mediumCVE-2026-56404: libexpat before 2.8.2 has an integer overflow in addBinding.msrc · 2026-06-09
• mediumCVE-2026-56412: libexpat before 2.8.2 does not consider XML_TOK_DATA_CHARS in doCdataSection and thus lacks ha…msrc · 2026-06-09

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