Vulnerability · Published Oct 8, 2026 · Assigned by GitHub_M

CVE-2026-107296msgpack5: Decoding negative int64 values mutates the input buffer

Low 3.7

In plain English

A low-severity security flaw in msgpack5 from mcollina. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 20% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.7Low

Exploit odds (30 days)0.3%top 79.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, decoding a negative signed 64-bit integer modifies the corresponding bytes in the caller-provided input buffer while computing the value. Applications that retain or reuse encoded input for integrity checks, logging, or later processing can observe silently corrupted data, while positive integers and other MessagePack value types are unaffected. This issue is fixed in version 6.1.0.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	msgpack5	6.1.0	GHSA-qw35-55vc-rhgj

Affected products (as reported)

Vendor	Product	Versions
mcollina	msgpack5	< 6.1.0

Weakness: CWE-471 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

References

https://github.com/mcollina/msgpack5/security/advisories/GHSA-qw35-55vc-rhgj x_refsource_CONFIRM
https://github.com/mcollina/msgpack5/commit/82b70393a824e1088a45a377548d1d9ab82faf91 x_refsource_MISC
https://github.com/mcollina/msgpack5/releases/tag/v6.1.0 x_refsource_MISC