CVE-2026-59876 PUBLISHED

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.

• https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934
• https://github.com/protobufjs/protobuf.js/pull/2335
• https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8
• https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5

• CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution') CWE