{"id":"CVE-2026-59876","aliases":["GHSA-jfj6-75fj-8934"],"url":"https://o3.security/vulnerability/CVE-2026-59876","summary":"protobufjs: Text Format string map parsing can mutate returned map object prototype","details":"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.","published":"2026-07-08T15:31:11.421Z","modified":"2026-08-12T03:51:29.345479361Z","cvss":{"score":4.8,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N"},"epss":{"score":0.00349,"percentile":0.27924,"asOf":"2026-09-07"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"protobufjs","fixedVersion":"8.6.5"}],"fix":{"url":"https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8","label":"protobufjs/protobuf.js@9f97fe4"},"references":[{"type":"WEB","url":"https://github.com/protobufjs/protobuf.js/releases/tag/protobufjs-v8.6.5"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/59xxx/CVE-2026-59876.json"},{"type":"ADVISORY","url":"https://github.com/protobufjs/protobuf.js/security/advisories/GHSA-jfj6-75fj-8934"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-59876"},{"type":"FIX","url":"https://github.com/protobufjs/protobuf.js/commit/9f97fe413072d3beb52c74e62d88ea8adc9444d8"},{"type":"FIX","url":"https://github.com/protobufjs/protobuf.js/pull/2335"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:29.345479361Z"}}