CVE-2026-59876
protobufjs: Text Format string map parsing can mutate returned map object prototype
Description
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.
INFO
Published Date :
July 8, 2026, 4:16 p.m.
Last Modified :
July 13, 2026, 3:02 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | MEDIUM | [email protected] | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update protobufjs to version 8.6.5 or later.
- Review and sanitize map entry keys.
- Avoid using '__proto__' as a map key.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-59876.
| URL | Resource |
|---|---|
| https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8 | Patch |
| https://github.com/protobufjs/protobuf.js/pull/2335 | Issue Tracking Patch |
| https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5 | Product Release Notes |
| https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934 | Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-59876 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-59876
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-59876 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-59876 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Jul. 13, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Added CPE Configuration OR *cpe:2.3:a:protobufjs_project:protobufjs:*:*:*:*:*:node.js:*:* versions from (including) 8.2.0 up to (excluding) 8.6.5 Added Reference Type GitHub, Inc.: https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/protobufjs/protobuf.js/pull/2335 Types: Issue Tracking, Patch Added Reference Type GitHub, Inc.: https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5 Types: Product, Release Notes Added Reference Type GitHub, Inc.: https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934 Types: Mitigation, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jul. 09, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-59876', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-07-09T14:41:36.435616Z'} -
New CVE Received by [email protected]
Jul. 08, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'protobufjs', 'product': 'protobuf.js', 'versions': [{'status': 'affected', 'version': '>= 8.2.0, < 8.6.5'}]}] Added Description 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. Added CVSS V3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Added CWE CWE-1321 Added Reference https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8 Added Reference https://github.com/protobufjs/protobuf.js/pull/2335 Added Reference https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5 Added Reference https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934