Medium 4.8Published Jul 8, 2026

CVE-2026-59876protobufjs: Text Format string map parsing can mutate returned map object prototype

Updated under an hour ago (Oct 26, 2026, 8:30 PM ET)

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It affects protobufjs protobuf.js and 1 other product. Add what you run to find out whether that includes you.

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Every CVE for protobufjs protobuf.js

Exploited in the last 30 days

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: 4.8 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
Weakness (CWE): CWE-1321
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Analyzed
Record last updated: Jul 9, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

protobufjs protobuf.js protobufjs:protobuf.js (from the name)	from 8.2.0, < 8.6.5	CNA record
protobufjs_project protobufjs protobufjs_project:protobufjs	from 8.2.0 before 8.6.5	NVD

References

References

https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934	x-refsource-confirm, mitigation, vendor-advisory
https://github.com/protobufjs/protobuf.js/pull/2335	x-refsource-misc, issue-tracking, patch
https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8	x-refsource-misc, patch
https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5	x-refsource-misc, product, release-notes

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.