# CVE-2026-76641: Expat Out-of-Bounds Read via dtdCopy

> Attackers can trigger memory corruption and denial of service in libexpat by processing malicious XML with external entity parsers.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Aug 2026
- **Updated:** 1 Oct 2026
- **Also known as:** ALPINE-CVE-2026-76641, AZL-96932, BELL-CVE-2026-76641, CLSA-2026-1791324825, CLSA-2026-1791325909, CLSA-2026-1791326154, ECHO-0ffe-8d46-73ca, GHSA-r6r4-8m79-7vvv, UBUNTU-CVE-2026-76641

## What is CVE-2026-76641?

CVE-2026-76641 is a high-severity memory corruption vulnerability in libexpat, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Expat through 2.8.3 contains an out-of-bounds read vulnerability that allows attackers to trigger memory corruption by processing XML with external entity parsers created via XML_ExternalEntityParserCreate. A struct size mismatch between ELEMENT_TYPE members causes storeAtts to read the attIndex member past allocated memory boundaries, resulting in failure to normalize whitespace in non-CDATA attributes or a wild pointer dereference causing a segfault. This vulnerability was introduced by the fix for CVE-2026-66046.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-76641?


## How do I fix CVE-2026-76641?

Apply the vendor's patch.

## Is CVE-2026-76641 being exploited?

There is no known exploitation of CVE-2026-76641 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-76641 and fix it if it is affected.

What it is: CVE-2026-76641 is a high-severity memory corruption vulnerability in libexpat, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-76641 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-2026-76641/ (Markdown: https://insights.sbomify.com/CVE-2026-76641/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-76641
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-76641
- OSV: https://osv.dev/vulnerability/CVE-2026-76641

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-76641/
Summaries are generated and may contain mistakes; the official description above is the record.