Executive Summary

This vulnerability is a prototype pollution issue in the JavaScript library Mafintosh's protocol-buffers-schema version 3.6.0. Prototype pollution allows an attacker to manipulate the prototype of base objects, which can lead to unexpected behavior in the application.

Specifically, an attacker exploiting this vulnerability may alter the application logic, bypass security checks, cause a denial of service (DoS), or even achieve remote code execution.

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Impact Analysis

Exploiting this vulnerability can have serious impacts including:

• Alteration of application logic, potentially changing how the software behaves.
• Bypassing security checks, which can lead to unauthorized access or actions.
• Causing denial of service (DoS), making the application unavailable.
• Achieving remote code execution, allowing attackers to run arbitrary code on the affected system.

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Compliance Impact

CVE-2026-5758 enables prototype pollution in the protocol-buffers-schema package, allowing attackers to alter application logic, bypass authentication, cause denial of service, or achieve remote code execution.

Such impacts can lead to unauthorized access to sensitive data or disruption of services, which may result in non-compliance with regulations like GDPR or HIPAA that require protection of personal data and system integrity.

Specifically, authentication bypass and remote code execution could expose or manipulate protected health information or personal data, violating confidentiality and security requirements mandated by these standards.

Therefore, failure to patch or mitigate this vulnerability could increase the risk of regulatory violations due to compromised data security and privacy controls.

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Detection Guidance

This vulnerability can be detected by checking if the protocol-buffers-schema package in your Node.js environment is vulnerable to prototype pollution via parsing malicious .proto files containing the key __proto__ in field options.

A practical detection method is to test parsing a crafted .proto schema that attempts to inject a property into Object.prototype and then verify if the property appears on plain objects.

• Create a test .proto file with a field option containing [( __proto__ ).polluted = "HACKED"]
• Run a Node.js script that uses protocol-buffers-schema to parse this malicious .proto file.
• After parsing, check if ({}).polluted returns "HACKED" indicating prototype pollution.

Example command snippet in Node.js:

• const schema = require('protocol-buffers-schema');
• const fs = require('fs');
• const proto = fs.readFileSync('malicious.proto', 'utf8');
• schema.parse(proto);
• console.log(({}).polluted); // Should output "HACKED" if vulnerable

Monitoring network traffic for suspicious .proto files containing __proto__ keys or scanning code repositories for usage of vulnerable versions (prior to 3.6.1) can also help detect exposure.

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Mitigation Strategies

The primary immediate mitigation step is to update the protocol-buffers-schema package to version 3.6.1 or later, where the vulnerability is fixed.

Additional mitigation steps include:

• Audit and restrict the source of .proto files to trusted inputs only, avoiding untrusted or semi-trusted sources.
• Review downstream code for prototype pollution exploitation vectors, especially in template engines, ORMs, and HTTP frameworks.
• Consider applying defense-in-depth measures such as freezing Object.prototype using Object.freeze(Object.prototype) in security-sensitive environments.
• For maintainers, avoid using reduce or bracket notation on user-controlled paths without filtering dangerous keys like __proto__, constructor, and prototype.

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