CVE-2026-107296: msgpack5 Decoding Negative Int64 Values Mutates Vulnerability

LOW
Advisory Identifier: GHSA-qw35-55vc-rhgj
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CVSS 3.7
CWE-471
Published
Advisory Summary

CVE-2026-107296 is a LOW (CVSS 3.7) decoding negative int64 values mutates vulnerability (CWE-471: Modification of Assumed-Immutable Data (MAID)) affecting msgpack5 libraries in the npm ecosystem. The issue involves decoding negative int64 values mutates the input buffer. Remediation is available by upgrading affected packages to version 6.1.0.

CVE-2026-107296 at a Glance

CVE Identifier CVE-2026-107296
GHSA Identifier GHSA-qw35-55vc-rhgj
Severity LOW
CVSS v3.1 Base Score 3.7
CWE Classification CWE-471: Modification of Assumed-Immutable Data (MAID)
Affected Product msgpack5
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 3.7

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2026-107296

To remediate this vulnerability, upgrade all affected msgpack5 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

msgpack5 fixed: 6.1.0 
npm install msgpack5@6.1.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

npm ls msgpack5

How to Check if You Are Affected

To determine whether your Node.js application is affected by CVE-2026-107296, inspect your project dependencies using npm:

npm ls msgpack5

Analyze the terminal output to locate any version of msgpack5 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.1.0), your application is affected.

Note: The npm ls msgpack5 command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-471: Modification of Assumed-Immutable Data (MAID), where the product does not properly protect an assumed-immutable element from being modified by an attacker. In msgpack5, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact Decoding a negative signed 64-bit integer modifies the corresponding bytes in the caller-provided input buffer. Applications that retain or reuse encoded input for integrity checks, logging, or subsequent processing may observe silently corrupted data. Positive integers and other MessagePack value types are not affected. ### Patches The decoder now computes signed 64-bit values without writing to the input buffer. ### Workarounds Copy untrusted MessagePack input before decoding it, or do not retain or reuse input buffers after decoding.

CVE-2026-107296 Affected msgpack5 Versions

1 component(s)
Fixed Versions:
6.1.0
Product / Package Ecosystem Affected Versions Fixed Version
msgpack5
npm/msgpack5
npm
< 6.1.0
6.1.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/mcollina/msgpack5/security/advisories/GHSA-qw35-55vc-rhgj
Security Fix Commit FIX COMMIT
https://github.com/mcollina/msgpack5/commit/82b70393a824e1088a45a377548d1d9ab82faf91
msgpack5 Source Repository REPOSITORY
https://github.com/mcollina/msgpack5
msgpack5 Release RELEASE
https://github.com/mcollina/msgpack5/releases/tag/v6.1.0

Frequently Asked Questions

What is CVE-2026-107296?
CVE-2026-107296 is a security vulnerability in msgpack5 involving Decoding negative int64 values mutates the input buffer under CWE-471: Modification of Assumed-Immutable Data (MAID).
Which msgpack5 versions are affected?
Affected versions include releases prior to 6.1.0 across affected packages: msgpack5.
What version fixes CVE-2026-107296?
Upgrading to 6.1.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is msgpack5 affected?
Yes, msgpack5 is affected in releases prior to 6.1.0. Upgrade your dependency to 6.1.0 or later.
What is the CVSS score of CVE-2026-107296?
CVE-2026-107296 has a CVSS v3.1 base score of 3.7 (LOW) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
What CWE is associated with CVE-2026-107296?
CVE-2026-107296 is classified under CWE-471: Modification of Assumed-Immutable Data (MAID) (The product does not properly protect an assumed-immutable element from being modified by an attacker.).
How can I check npm dependencies for CVE-2026-107296?
Run the dependency tree command: 'npm ls msgpack5'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-qw35-55vc-rhgj",
  "modified" : "2026-10-08T17:39:30Z",
  "published" : "2026-10-08T17:39:30Z",
  "aliases" : [ "CVE-2026-107296" ],
  "summary" : "msgpack5: Decoding negative int64 values mutates the input buffer",
  "details" : "### Impact\n\nDecoding a negative signed 64-bit integer modifies the corresponding bytes in the caller-provided input buffer. Applications that retain or reuse encoded input for integrity checks, logging, or subsequent processing may observe silently corrupted data.\n\nPositive integers and other MessagePack value types are not affected.\n\n### Patches\n\nThe decoder now computes signed 64-bit values without writing to the input buffer.\n\n### Workarounds\n\nCopy untrusted MessagePack input before decoding it, or do not retain or reuse input buffers after decoding.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "msgpack5"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "6.1.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/mcollina/msgpack5/security/advisories/GHSA-qw35-55vc-rhgj"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mcollina/msgpack5/commit/82b70393a824e1088a45a377548d1d9ab82faf91"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mcollina/msgpack5"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mcollina/msgpack5/releases/tag/v6.1.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-471" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-08T17:39:30Z",
    "nvd_published_at" : null
  }
}