---
id: CVE-2026-59876
title: protobufjs compiles protobuf definitions into JavaScript (JS) functions
summary: >-
  protobufjs compiles protobuf definitions into JavaScript (JS) functions. From
  8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed
  map entries using ordinary property assignment, allowing a map entry with key
  __pro…
severity: medium
cvss: 4.8
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N'
cwe:
  - CWE-1321
vendor: protobufjs_project
product: protobufjs
affected:
  - 'protobufjs >= 8.2.0, < 8.6.5'
patched:
  - protobufjs 8.6.5
published: '2026-07-08'
updated: '2026-07-13'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-59876'
references:
  - url: >-
      https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8
    label: security-advisories@github.com
  - url: 'https://github.com/protobufjs/protobuf.js/pull/2335'
    label: security-advisories@github.com
  - url: 'https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5'
    label: security-advisories@github.com
  - url: >-
      https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934
    label: security-advisories@github.com
tags:
  - nvd
epss: 0.00349
epssPercentile: 0.25861
ingestedAt: '2026-07-13T15:27:34.188Z'
---

## Overview

protobufjs compiles protobuf definitions into JavaScript (JS) functions. From 8.2.0 until 8.6.5, the protobufjs Text Format extension parsed string-keyed map entries using ordinary property assignment, allowing a map entry with key __proto__ to change the prototype of the returned map object instead of creating an own map entry in protobufjs/ext/textformat. This issue is fixed in version 8.6.5.

## Affected

- `protobufjs >= 8.2.0, < 8.6.5`

## Remediation

Upgrade past the affected range:

- `protobufjs 8.6.5`