# CVE-2017-16931: XML external entity in n/a

> An attacker can exploit improper handling of parameter-entity references in libxml2 to cause denial of service or read sensitive data.

- **Severity:** Critical 9.8 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Nov 2017
- **Updated:** 14 Oct 2026
- **Also known as:** ALPINE-CVE-2017-16931, DEBIAN-CVE-2017-16931, ECHO-b059-acf0-0ac1, GHSA-7mr2-r9fx-7j9m

## What is CVE-2017-16931?

CVE-2017-16931 is a critical vulnerability in Xmlsoft Libxml2, published on 23 Nov 2017. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

parser.c in libxml2 before 2.9.5 mishandles parameter-entity references because the NEXTL macro calls the xmlParserHandlePEReference function in the case of a '%' character in a DTD name.

Weakness: CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer)

## Which versions are affected by CVE-2017-16931?

It affects 1 product.


Products: Xmlsoft Libxml2.

## How do I fix CVE-2017-16931?

Upgrade to a fixed version.

## Is CVE-2017-16931 being exploited?

There is no known exploitation of CVE-2017-16931 in the wild and no public exploit code.

## Other vulnerabilities in Xmlsoft Libxml2

- [CVE-2017-8872](https://insights.sbomify.com/CVE-2017-8872/): Information disclosure in n/a (critical 9.1)
- [CVE-2022-49043](https://insights.sbomify.com/CVE-2022-49043/): Use after free in libxml2 (high 8.1)
- [CVE-2026-86140](https://insights.sbomify.com/CVE-2026-86140/): Memory corruption in libxml2 (high 8.0)
- [CVE-2024-34459](https://insights.sbomify.com/CVE-2024-34459/): Memory corruption in n/a (high 7.5)
- [CVE-2024-25062](https://insights.sbomify.com/CVE-2024-25062/): Use after free in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2017-16931 and fix it if it is affected.

What it is: CVE-2017-16931 is a critical vulnerability in Xmlsoft Libxml2, published on 23 Nov 2017. 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-2017-16931 in the wild and no public exploit code.

Affected product: Xmlsoft Libxml2. 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-2017-16931/ (Markdown: https://insights.sbomify.com/CVE-2017-16931/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2017-16931
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-16931
- OSV: https://osv.dev/vulnerability/CVE-2017-16931

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From sbomify Insights: https://insights.sbomify.com/CVE-2017-16931/
Summaries are generated and may contain mistakes; the official description above is the record.