Vulnerability in protobufjs (CVE-2026-59876)
Summary
Vulnerability in protobufjs (CVE-2026-59876). Risk of unauthorized operations or information disclosure. Exploitable via __proto__. Mitigation: upgrade to 8.6.5 or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-59876 has been found in protobufjs.
Attackers can target a specific entry point like __proto__ over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.8/10.
What to do: upgrade protobufjs to 8.6.5 or later.
If unsure, ask your IT team or search "protobufjs CVE-2026-59876" on the vendor's site.
CVE-2026-59876 (protobufjs) — CWE-1321 / CVSS v3 4.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: __proto__ / fromObject / Object.prototype
Patched: 8.6.5 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-1321) exists in protobufjs. Attackers reach the vulnerable code path via __proto__ without authentication.
Check the vendor advisory for the affected versions of protobufjs. Attack surface: __proto__ / fromObject / Object.prototype.
Severity: Medium (CVSS 4.8/10). Risk of unauthorized operations or information disclosure.
Update to 8.6.5.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'protobufjs' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'protobufjs' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
protobufjsを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade protobufjs to 8.6.5ステージング環境で 8.6.5 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- patch github.com
- patch github.com
- web github.com
- web github.com