Use-After-Free in libexpat (CVE-2026-56131)
Summary
Vulnerability in libexpat (CVE-2026-56131). Risk of unauthorized operations or information disclosure.
Original description
The description as published by the source.
libexpat before 2.8.2 lacks handler call depth tracking for calls to XML_ResumeParser from within handlers in cases of a policy violation. Thus, a use-after-free can occur (similar to the CVE-2026-50219 situation).
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-56131 has been found in libexpat.
Risk of unauthorized operations or information disclosure. CVSS score: 4.9/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "libexpat CVE-2026-56131" on the vendor's site.
CVE-2026-56131 (libexpat) — CWE-416 / CVSS v3 4.9
Attack vector: local / unauthenticated / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Use-after-free (CWE-416) exists in libexpat.
Check the vendor advisory for the affected versions of libexpat.
Severity: Medium (CVSS 4.9/10). Risk of unauthorized operations or information disclosure.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'libexpat' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'libexpat' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
libexpatを grep し、稼働しているサービス・バージョンを把握する。 -
2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Alpine Linux ALPINE-CVE-2026-56131 expat Fixed in: 2.8.2-r0
- BellSoft Alpaquita BELL-CVE-2026-56131 expat Fixed in: 2.8.2-r0
- Debian DEBIAN-CVE-2026-56131 expat Fixed in: 2.5.0-1+deb12u3
- Ubuntu UBUNTU-CVE-2026-56131 coin3
References
- patch cve@mitre.org
- web nvd.nist.gov
- web github.com