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PatchSiren cyber security CVE debrief

CVE-2026-56411 libexpat project CVE debrief

CVE-2026-56411 is a medium-severity vulnerability (CVSS score of 6.9) affecting libexpat before version 2.8.2. The issue is an integer overflow in the endDoctypeDecl function, which occurs via NOTATION declarations. This vulnerability could potentially allow local attackers with specific conditions to execute arbitrary code. The disclosure date is June 21, 2026, and defenders should prioritize patching or mitigating this vulnerability to limit exposure.

Vendor
libexpat project
Product
libexpat
CVSS
MEDIUM 6.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-06-21
Original CVE updated
2026-06-23
Advisory published
2026-06-21
Advisory updated
2026-06-23

Who should care

Defenders managing systems or applications that utilize libexpat, especially versions prior to 2.8.2, should be aware of this vulnerability. This includes developers, system administrators, and cybersecurity professionals responsible for maintaining software dependencies. Given the medium severity and potential for local exploitation, prioritizing patching or mitigation efforts is advisable.

Technical summary

The CVE-2026-56411 vulnerability is caused by an integer overflow in the endDoctypeDecl function of libexpat, a widely-used XML parsing library. This overflow occurs when processing NOTATION declarations in XML files. Successful exploitation could lead to arbitrary code execution, although the CVSS score of 6.9 indicates a medium level of severity. The vulnerability is addressed in libexpat version 2.8.2 or later.

Defensive priority

Medium priority due to CVSS score of 6.9 and potential for local code execution.

Recommended defensive actions

  • Inventory and assess the exposure of systems or applications using libexpat versions prior to 2.8.2.
  • Apply patches or updates to libexpat to version 2.8.2 or later.
  • Review and implement compensating controls if immediate patching is not feasible.
  • Monitor for and track any exceptions or workarounds applied due to this vulnerability.

Evidence notes

The primary evidence for this vulnerability comes from the CVE record and NVD detail pages. The vulnerability affects libexpat versions before 2.8.2. Defenders should verify the version of libexpat in use and check for official advisories or patches from the vendor.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-56411 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-56411

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-56411 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-56411

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.