# CVE-2026-107301: msgpack5: Partial options disable prototype protection

> Attackers can exploit prototype pollution in msgpack5 when using partial options, potentially leading to code execution or privilege escalation.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 Oct 2026
- **Updated:** 14 Oct 2026
- **Also known as:** AZL-106857, GHSA-8hq7-ggx2-cc6m

## What is CVE-2026-107301?

CVE-2026-107301 is a medium-severity unsafe deserialization vulnerability in mcollina msgpack5, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, constructing msgpack5 with an empty or partial options object disables the default protoAction: 'error' protection. A decoded map containing a __proto__ key can then replace the decoded object's prototype, potentially changing inherited properties or downstream behavior, although Object.prototype is not modified globally. This issue is fixed in version 6.1.0.

Weakness: CWE-1321 (Improperly Controlled Modification of Object Prototype Attributes)

## Which versions are affected by CVE-2026-107301?

2 open source packages ship an affected version, including msgpack5.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `msgpack5` | npm | All versions | 6.1.0 |
| `msgpack5` | npm | All versions | 6.1.0 |

## How do I fix CVE-2026-107301?

Upgrade msgpack5 to 6.1.0 or later.

## Is CVE-2026-107301 being exploited?

There is no known exploitation of CVE-2026-107301 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-107301 and fix it if it is affected.

What it is: CVE-2026-107301 is a medium-severity unsafe deserialization vulnerability in mcollina msgpack5, published on 8 Oct 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-2026-107301 in the wild and no public exploit code.

Affected packages and fixed versions:
- msgpack5 (npm): affected all versions; fixed in 6.1.0
- msgpack5 (npm): affected all versions; fixed in 6.1.0

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-2026-107301/ (Markdown: https://insights.sbomify.com/CVE-2026-107301/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-107301
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-107301
- OSV: https://osv.dev/vulnerability/CVE-2026-107301

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-107301/
Summaries are generated and may contain mistakes; the official description above is the record.