High · CVSS 7.5CVE-2026-107302GHSA-8F34-F56X-9XPH

msgpack5: Truncated map32 headers throw an unexpected errorCVE-2026-107302

Answer in brief

CVE-2026-107302 records a High severity (CVSS 7.5) vulnerability in msgpack5: Truncated map32 headers throw an unexpected error. The current sources do not mark it as known exploited. The current feed maps mcollina/msgpack5 (generic), msgpack5 (npm). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Oct 8, 2026Updated Oct 8, 2026Source checked Oct 8, 2026First seen by HOL Oct 8, 2026Material review Oct 8, 2026

Upstream Advisory

Key facts

Risk: High · CVSS 7.5
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps mcollina/msgpack5 (generic), msgpack5 (npm). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
mcollina/msgpack5generic	<6.1.0	6.1.0
msgpack5npm	<6.1.0	6.1.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for mcollina/msgpack5, msgpack5.
Review the reported fix. Update mcollina/msgpack5 to 6.1.0; msgpack5 to 6.1.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Oct 8, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.