CVE-2026-59876

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 3.1

4.8CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS

0.3% chance of exploitation in the next 30 days; higher than 28% of CVEs (scores of 2026-10-25)

CWE

CWE-1321

Published

2026-07-08

Modified

2026-10-25

Record from

the NVD, synced 2026-10-25

Affected

• protobufjs_project:protobufjs

Packages (OSV)

References

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

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