CVE-2020-7768: Grpc Prototype Pollution Vulnerability

CVE-2020-7768 Overview

CVE-2020-7768 is a Prototype Pollution vulnerability affecting the gRPC Node.js packages. The package grpc before version 1.24.4 and the package @grpc/grpc-js before version 1.1.8 are vulnerable to Prototype Pollution via the loadPackageDefinition function. This vulnerability allows attackers to inject properties into JavaScript object prototypes, potentially leading to remote code execution, denial of service, or other security impacts.

Critical Impact

Attackers can exploit this Prototype Pollution vulnerability to modify application behavior, bypass security controls, or achieve remote code execution through maliciously crafted gRPC package definitions.

Affected Products

• grpc (Node.js package) versions before 1.24.4
• @grpc/grpc-js versions before 1.1.8
• org.webjars.npm:grpc (Java WebJars wrapper)

Discovery Timeline

• November 11, 2020 - CVE-2020-7768 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-7768

Vulnerability Analysis

This vulnerability is classified as Prototype Pollution (CWE-1321), a class of vulnerabilities specific to JavaScript applications. The flaw exists in the loadPackageDefinition function used to load gRPC protocol buffer definitions. When processing untrusted or maliciously crafted package definitions, the function fails to properly sanitize property names, allowing attackers to inject properties into the Object.prototype.

In JavaScript, all objects inherit from Object.prototype. When an attacker pollutes this prototype, every object in the application inherits the malicious properties. This can lead to various attack scenarios including property injection, security control bypass, and in some cases, remote code execution when combined with other application logic.

The vulnerability is network-exploitable without requiring authentication or user interaction, making it particularly dangerous in environments where gRPC services process untrusted input.

Root Cause

The root cause of this vulnerability lies in improper input validation within the loadPackageDefinition function. The function processes gRPC package definitions without sanitizing special property names such as __proto__, constructor, or prototype. When a malicious package definition contains these special properties with attacker-controlled values, the properties are written directly to the Object prototype instead of being treated as regular object properties.

Attack Vector

The attack vector is network-based, requiring an attacker to supply a maliciously crafted gRPC package definition to an application using the vulnerable loadPackageDefinition function. The exploitation flow involves:

1. The attacker crafts a malicious gRPC package definition containing prototype pollution payloads
2. The vulnerable application loads this definition using loadPackageDefinition
3. The function processes the malicious definition without proper sanitization
4. Properties are injected into Object.prototype, affecting all JavaScript objects
5. Depending on application logic, this can lead to authentication bypass, RCE, or DoS

The vulnerability can be exploited by providing package definitions with specially crafted property names that target the JavaScript prototype chain. Detailed technical analysis and proof-of-concept information can be found in the Snyk vulnerability advisory for grpc and the Snyk advisory for @grpc/grpc-js.

Detection Methods for CVE-2020-7768

Indicators of Compromise

• Unusual properties appearing on JavaScript objects that were not explicitly defined
• Application behavior changes related to authentication or authorization checks
• Unexpected errors or crashes in gRPC service handling code
• Log entries showing malformed or suspicious gRPC package definitions

Detection Strategies

• Monitor application dependencies for vulnerable versions of grpc (<1.24.4) and @grpc/grpc-js (<1.1.8)
• Implement runtime monitoring for prototype pollution attempts using JavaScript security libraries
• Use static analysis tools to scan for usage patterns of loadPackageDefinition with untrusted input
• Deploy Web Application Firewalls (WAF) configured to detect prototype pollution payloads in request bodies

Monitoring Recommendations

• Enable detailed logging for gRPC service definition loading operations
• Monitor for anomalous property access patterns on base JavaScript objects
• Implement integrity checks on application state to detect unexpected prototype modifications
• Set up alerts for dependency scanning tools to flag vulnerable gRPC package versions

How to Mitigate CVE-2020-7768

Immediate Actions Required

• Upgrade grpc package to version 1.24.4 or later immediately
• Upgrade @grpc/grpc-js package to version 1.1.8 or later immediately
• Audit applications for usage of loadPackageDefinition with untrusted input sources
• Review application logs for any signs of exploitation attempts

Patch Information

The gRPC maintainers have addressed this vulnerability in the following releases:

• grpc: Version 1.24.4 and later (GitHub Pull Request #1605)
• @grpc/grpc-js: Version 1.1.8 and later (GitHub Pull Request #1606)

Update your package dependencies using npm or yarn:

Workarounds

• Validate and sanitize all gRPC package definitions before passing them to loadPackageDefinition
• Implement Object freezing on critical prototypes using Object.freeze(Object.prototype) if application compatibility allows
• Use npm/yarn audit tools to identify and track vulnerable dependencies
• Consider using runtime prototype pollution prevention libraries such as nopp or similar security modules

# Upgrade grpc package to patched version
npm update grpc@1.24.4

# Upgrade @grpc/grpc-js to patched version
npm update @grpc/grpc-js@1.1.8

# Verify installed versions
npm list grpc @grpc/grpc-js

# Run npm audit to check for remaining vulnerabilities
npm audit