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CVE-2026-59877 medium CVSS 5.3

Vulnerability in protobufjs (CVE-2026-59877)

Summary

Vulnerability in protobufjs (CVE-2026-59877). Risk of unauthorized operations or information disclosure. Exploitable via parse. Mitigation: upgrade to 8.6.6 or later.

Original description

The description as published by the source.

Summary

protobufjs parsed option names by advancing through schema tokens until it reached an = token, without checking for end of input. A crafted .proto schema that opens an option declaration but ends prematurely could cause the option parser to loop without ever terminating.

This affects the reflection parsing path (parse, Root.load, Root.loadSync).

Impact

An attacker who can provide or influence .proto schema text parsed by an application may be able to cause the parsing call to never return. Because Node.js is single-threaded, the blocked event loop prevents all other work in the process, resulting in a denial of service that persists until the process is externally terminated.

Applications that only encode or decode protobuf binary data with trusted schemas are not directly affected.

Preconditions

  • The application must parse .proto schema text influenced by an attacker.
  • The schema must be parsed through APIs such as parse, Root.load, or Root.loadSync.
  • The crafted input must begin an option declaration that ends before its = assignment.

Workarounds

Do not parse .proto schemas from untrusted sources with affected versions. If untrusted schema text must be accepted, isolate parsing in a process or worker that can be safely terminated and bound it with a timeout, so a non-returning parse call cannot deny service to the rest of the application.

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-2026-59877 has been found in protobufjs.
Attackers can target a specific entry point like parse over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade protobufjs to 8.6.6 or later.
If unsure, ask your IT team or search "protobufjs CVE-2026-59877" on the vendor's site.

CVE-2026-59877 (protobufjs) — CWE-835 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: parse / Root.load / Root.loadSync
Patched: 8.6.6 — apply immediately
Workaround: Do not parse .proto schemas from untrusted sources with affected versions.
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.

❓ What is the problem

A vulnerability (CWE-835) exists in protobufjs. Attackers reach the vulnerable code path via parse without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of protobufjs. Attack surface: parse / Root.load / Root.loadSync.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 8.6.6.

🛡️ Workaround

Workaround: Do not parse .proto schemas from untrusted sources with affected versions.

🔍 Detection

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

  1. 1
    Identify 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。

  2. 2
    Apply temporary workaround mitigate 
    Do not parse `.proto` schemas from untrusted sources with affected versions.

    パッチが適用されるまでの応急処置として、Do not parse .proto schemas from untrusted sources with affected versions. を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade protobufjs to 8.6.6

    ステージング環境で 8.6.6 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。

  4. 4
    Post-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

npm protobufjs
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"8.6.6"}]}]

References

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