CVE-2026-59876: CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in protobufjs protobuf.js
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.
AI Analysis
Technical Summary
protobufjs is a JavaScript library that compiles protobuf definitions into JS functions. Between versions 8.2.0 and 8.6.4 inclusive, the Text Format extension improperly handles string-keyed map entries by assigning them directly to object properties. This allows an attacker to use the key '__proto__' to modify the prototype of the map object, leading to prototype pollution (CWE-1321). This can cause unexpected behavior or security issues in applications using affected versions. The vulnerability is addressed in version 8.6.5.
Potential Impact
An attacker can manipulate the prototype of objects returned by the protobufjs Text Format extension, potentially altering application behavior or causing security issues related to prototype pollution. The CVSS score is 4.8 (medium severity), indicating limited impact with network attack vector, high attack complexity, no privileges required, no user interaction, and low confidentiality and integrity impact with no availability impact.
Mitigation Recommendations
Upgrade protobufjs to version 8.6.5 or later, where this prototype pollution vulnerability is fixed. Patch status is confirmed by the version fix information. No other mitigations are specified.
CVE-2026-59876: CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') in protobufjs protobuf.js
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.
CVSS v3.1
Score 4.8medium
Affected software
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
protobufjs is a JavaScript library that compiles protobuf definitions into JS functions. Between versions 8.2.0 and 8.6.4 inclusive, the Text Format extension improperly handles string-keyed map entries by assigning them directly to object properties. This allows an attacker to use the key '__proto__' to modify the prototype of the map object, leading to prototype pollution (CWE-1321). This can cause unexpected behavior or security issues in applications using affected versions. The vulnerability is addressed in version 8.6.5.
Potential Impact
An attacker can manipulate the prototype of objects returned by the protobufjs Text Format extension, potentially altering application behavior or causing security issues related to prototype pollution. The CVSS score is 4.8 (medium severity), indicating limited impact with network attack vector, high attack complexity, no privileges required, no user interaction, and low confidentiality and integrity impact with no availability impact.
Mitigation Recommendations
Upgrade protobufjs to version 8.6.5 or later, where this prototype pollution vulnerability is fixed. Patch status is confirmed by the version fix information. No other mitigations are specified.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-07-07T15:41:53.607Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a4e73c2c9d9e3dbe36042d4
Added to database: 07/08/2026, 15:58:58 UTC
Last enriched: 07/16/2026, 10:06:53 UTC
Last updated: 08/22/2026, 10:52:10 UTC
Views: 118
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