CVE-2026-107301: msgpack5 Partial Options Disable Prototype Protection Vulnerability

MODERATE
Advisory Identifier: GHSA-8hq7-ggx2-cc6m
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CVSS 6.5
CWE-1321
Published
Advisory Summary

CVE-2026-107301 is a MODERATE (CVSS 6.5) partial options disable prototype protection vulnerability (CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')) affecting msgpack5 libraries in the npm ecosystem. The issue involves partial options disable prototype protection. Remediation is available by upgrading affected packages to version 6.1.0.

CVE-2026-107301 at a Glance

CVE Identifier CVE-2026-107301
GHSA Identifier GHSA-8hq7-ggx2-cc6m
Severity MODERATE
CVSS v3.1 Base Score 6.5
CWE Classification CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
Affected Product msgpack5
Package Ecosystem npm
Published Date
Last Updated

Security Impact

CVSS: 6.5

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:H/A:L).

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 High (I:H)
Availability Low (A:L)

How to Fix CVE-2026-107301

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-2026-107301, 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-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution'), where the product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype. 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 Passing an empty or partial options object disables the default `protoAction: 'error'` protection. A map containing a `__proto__` key can then replace the prototype of the decoded object, potentially changing inherited properties or causing unexpected behavior in downstream code. Only the decoded object's prototype is affected; this does not modify `Object.prototype` globally. ### Patches Options are now merged with secure defaults without modifying the caller's object. Unsupported `protoAction` values are rejected. ### Workarounds Explicitly set `protoAction: 'error'` whenever constructing a msgpack5 instance, and validate decoded values before use.

CVE-2026-107301 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-8hq7-ggx2-cc6m
Security Fix Commit FIX COMMIT
https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774
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-2026-107301?
CVE-2026-107301 is a security vulnerability in msgpack5 involving Partial options disable prototype protection under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution').
Which msgpack5 versions are affected?
Affected versions include releases prior to 6.1.0 across affected packages: msgpack5.
What version fixes CVE-2026-107301?
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-2026-107301?
CVE-2026-107301 has a CVSS v3.1 base score of 6.5 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L.
What CWE is associated with CVE-2026-107301?
CVE-2026-107301 is classified under CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') (The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.).
How can I check npm dependencies for CVE-2026-107301?
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-8hq7-ggx2-cc6m",
  "modified" : "2026-10-08T17:39:57Z",
  "published" : "2026-10-08T17:39:57Z",
  "aliases" : [ "CVE-2026-107301" ],
  "summary" : "msgpack5: Partial options disable prototype protection",
  "details" : "### Impact\n\nPassing an empty or partial options object disables the default `protoAction: 'error'` protection. A map containing a `__proto__` key can then replace the prototype of the decoded object, potentially changing inherited properties or causing unexpected behavior in downstream code.\n\nOnly the decoded object's prototype is affected; this does not modify `Object.prototype` globally.\n\n### Patches\n\nOptions are now merged with secure defaults without modifying the caller's object. Unsupported `protoAction` values are rejected.\n\n### Workarounds\n\nExplicitly set `protoAction: 'error'` whenever constructing a msgpack5 instance, and validate decoded values before use.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:L"
  } ],
  "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-8hq7-ggx2-cc6m"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mcollina/msgpack5/commit/20e82600ac9462e679c8a45e5723315f21e2c774"
  }, {
    "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-1321" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-08T17:39:57Z",
    "nvd_published_at" : null
  }
}