---
title: "CVE-2026-107300: msgpack5 - Denial of Service"
description: "msgpack5 prior to 6.1.0 contains a denial of service caused by recursive invocation of the streaming decoder on multiple small valid values in a chunk, letting remote attackers exhaust the JavaScript call stack, exploit requires sending crafted chunk with many values."
url: https://panop.io/threat-heartbeat/CVE-2026-107300/
---

# CVE-2026-107300 msgpack5 - Denial of Service

msgpack5 prior to 6.1.0 contains a denial of service caused by recursive invocation of the streaming decoder on multiple small valid values in a chunk, letting remote attackers exhaust the JavaScript call stack, exploit requires sending crafted chunk with many values.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

Authentication

Not required

EPSS

0.43% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-107300)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published

8 October 2026

Updated

15 October 2026

Weakness

[CWE-674](https://cwe.mitre.org/data/definitions/674.html)

## Vendor fix

Upgrade to version 6.1.0 or later.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-107300](https://nvd.nist.gov/vuln/detail/CVE-2026-107300)
- [https://github.com/mcollina/msgpack5/security/advisories/GHSA-5x5g-h9x8-2fh9](https://github.com/mcollina/msgpack5/security/advisories/GHSA-5x5g-h9x8-2fh9)
- [https://github.com/mcollina/msgpack5/commit/77fbef144d05def5d16fc22c37caa64c0a7efeba](https://github.com/mcollina/msgpack5/commit/77fbef144d05def5d16fc22c37caa64c0a7efeba)
- [https://github.com/mcollina/msgpack5/releases/tag/v6.1.0](https://github.com/mcollina/msgpack5/releases/tag/v6.1.0)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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