# CVE-2026-118370: libexpat through 2.9.0 Integer Overflow in storeAtts via attIndex and nPrefixes


- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** Yes
- **Published:** 28 Oct 2026
- **Updated:** 28 Oct 2026
- **Also known as:** AZL-111148, DEBIAN-CVE-2026-118370, ECHO-716b-5eac-638d, GHSA-c6pw-vjr4-wwwr, UBUNTU-CVE-2026-118370

## What is CVE-2026-118370?

CVE-2026-118370 is a high-severity vulnerability in libexpat, published on 28 Oct 2026. 

### Official description

libexpat through 2.9.0 contains a signed integer overflow vulnerability in storeAtts() in lib/xmlparse.c that allows attackers to trigger out-of-bounds writes via oversized attribute counts. Attackers can supply a multi-gigabyte document with a start tag carrying over 2^30 attributes to overflow attIndex and nPrefixes, crashing applications or corrupting heap memory.

Weakness: CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-118370?


## How do I fix CVE-2026-118370?

Upgrade to a fixed version.

## Is CVE-2026-118370 being exploited?

There is no known exploitation of CVE-2026-118370 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-118370 and fix it if it is affected.

What it is: CVE-2026-118370 is a high-severity vulnerability in libexpat, published on 28 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-118370 in the wild and no public exploit code.

Affected product: 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-2026-118370/ (Markdown: https://insights.sbomify.com/CVE-2026-118370/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-118370
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-118370
- OSV: https://osv.dev/vulnerability/CVE-2026-118370

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-118370/
Summaries are generated and may contain mistakes; the official description above is the record.