# CVE-2026-56406: libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check that was present in XML_Parse.


- **Severity:** Medium 6.9 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 21 Jun 2026
- **Updated:** 22 Jun 2026
- **Also known as:** ALPINE-CVE-2026-56406, AZL-90234, BELL-CVE-2026-56406, DEBIAN-CVE-2026-56406, ECHO-8fda-fcf5-f272, GHSA-v2j6-3q6q-gm3g, JLSEC-2026-1230, ROOT-OS-DEBIAN-11-CVE-2026-56406, UBUNTU-CVE-2026-56406

## What is CVE-2026-56406?

CVE-2026-56406 is a medium-severity vulnerability in Libexpat Project Libexpat, published on 21 Jun 2026. 

### Official description

libexpat before 2.8.2 has an integer overflow in XML_ParseBuffer because it lacked a check that was present in XML_Parse.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-56406?

It affects 1 product.


Products: Libexpat Project Libexpat.

## How do I fix CVE-2026-56406?

Upgrade to a fixed version.

## Is CVE-2026-56406 being exploited?

There is no known exploitation of CVE-2026-56406 in the wild and no public exploit code.

## Other vulnerabilities in Libexpat Project Libexpat

- [CVE-2024-45490](https://insights.sbomify.com/CVE-2024-45490/): Integer overflow in n/a (critical 9.8)
- [CVE-2026-66046](https://insights.sbomify.com/CVE-2026-66046/): Expat Denial of Service via storeAtts() Quadratic Complexity (high 8.7)
- [CVE-2021-46143](https://insights.sbomify.com/CVE-2021-46143/): Integer overflow in n/a (high 8.1)
- [CVE-2017-11742](https://insights.sbomify.com/CVE-2017-11742/): Privilege escalation in n/a (high 7.8)
- [CVE-2025-59375](https://insights.sbomify.com/CVE-2025-59375/): Denial of service in libexpat (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56406 and fix it if it is affected.

What it is: CVE-2026-56406 is a medium-severity vulnerability in Libexpat Project Libexpat, published on 21 Jun 2026. 
Exploitation: There is no known exploitation of CVE-2026-56406 in the wild and no public exploit code.

Affected product: Libexpat Project Libexpat. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-56406/ (Markdown: https://insights.sbomify.com/CVE-2026-56406/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56406
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56406
- OSV: https://osv.dev/vulnerability/CVE-2026-56406

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-56406/
Summaries are generated and may contain mistakes; the official description above is the record.