CVE-2020-7774: Y18n Prototype Pollution Vulnerability

CVE-2020-7774 Overview

CVE-2020-7774 is a Prototype Pollution vulnerability affecting the y18n package, a popular internationalization (i18n) library for Node.js applications. The y18n package versions before 3.2.2, 4.0.1, and 5.0.5 are vulnerable to prototype pollution attacks, which can allow attackers to manipulate the behavior of JavaScript applications by injecting properties into Object prototypes.

Critical Impact

This vulnerability enables attackers to inject arbitrary properties into JavaScript object prototypes via network-accessible vectors, potentially leading to remote code execution, denial of service, or authentication bypass in affected Node.js applications.

Affected Products

• y18n_project y18n (versions before 3.2.2, 4.0.1, and 5.0.5)
• Oracle GraalVM Enterprise (versions 19.3.5, 20.3.1.2, 21.0.0.2)
• Siemens SINEC Infrastructure Network Services

Discovery Timeline

• 2020-11-17 - CVE-2020-7774 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-7774

Vulnerability Analysis

Prototype Pollution is a JavaScript-specific vulnerability class (CWE-1321) that occurs when untrusted user input is merged into JavaScript objects without proper sanitization. In the case of y18n, the vulnerability exists in the library's internationalization functions that process locale data.

The y18n package provides simple i18n functionality for Node.js applications, allowing developers to manage translations and locale strings. The vulnerable code path allows attackers to inject properties like __proto__ or constructor.prototype through maliciously crafted locale data, which then pollutes the base Object prototype.

When the Object prototype is polluted, all objects in the application inherit the injected properties. This can lead to various attack scenarios including property injection that bypasses security checks, modification of application logic, denial of service through property conflicts, and in some cases, remote code execution when polluted properties are used in dangerous contexts like command execution or file operations.

Root Cause

The root cause of this vulnerability lies in the unsafe recursive merge operations within y18n's locale handling functions. The library fails to properly validate or sanitize special JavaScript properties such as __proto__, constructor, and prototype when processing user-controlled input. This allows attackers to traverse the prototype chain and inject malicious properties into the base Object prototype that all JavaScript objects inherit from.

Attack Vector

The vulnerability is exploitable via network-accessible vectors where attackers can supply malicious input to y18n's locale processing functions. This includes scenarios where locale files or translation strings are loaded from untrusted sources, where user input influences translation keys or values, or where APIs expose y18n functionality to external requests.

Exploitation involves crafting a payload that contains prototype pollution gadgets. When y18n processes this malicious input through its setLocale or similar functions, the properties are recursively merged into internal objects, ultimately polluting the Object prototype. Successful exploitation requires no authentication or privileges and does not require user interaction.

Detection Methods for CVE-2020-7774

Indicators of Compromise

• Unexpected properties appearing on JavaScript objects that were not explicitly defined
• Application behavior anomalies related to object property access returning unexpected values
• Error logs showing undefined method calls on objects due to prototype chain manipulation
• Anomalous network requests containing __proto__ or constructor keywords in JSON payloads

Detection Strategies

• Implement Software Composition Analysis (SCA) scanning to identify vulnerable y18n versions in your dependency tree
• Monitor application logs for JSON parsing errors or unexpected property access patterns
• Deploy runtime application self-protection (RASP) solutions capable of detecting prototype pollution attempts
• Use npm audit or similar dependency scanning tools to identify CVE-2020-7774 in your projects

Monitoring Recommendations

• Enable verbose logging for Node.js applications to capture unusual object manipulation events
• Monitor incoming HTTP requests for payloads containing prototype pollution patterns (__proto__, constructor.prototype)
• Implement content security policies and input validation layers at API boundaries
• Track dependency versions across your software supply chain for vulnerable y18n packages

How to Mitigate CVE-2020-7774

Immediate Actions Required

• Update y18n to version 3.2.2 or later for the 3.x branch
• Update y18n to version 4.0.1 or later for the 4.x branch
• Update y18n to version 5.0.5 or later for the 5.x branch
• Review and update Oracle GraalVM and Siemens SINEC Infrastructure Network Services per vendor advisories

Patch Information

The y18n maintainers have released patched versions that address this prototype pollution vulnerability. The fix is available in the GitHub Pull Request which implements proper sanitization of dangerous properties during object merging operations. Oracle has addressed this in their April 2021 CPU, and Siemens has published guidance in their Security Advisory SSA-389290.

Workarounds

• Implement input validation to reject objects containing __proto__, constructor, or prototype properties before passing data to y18n
• Use Object.freeze() on Object.prototype to prevent prototype modification at application startup
• Consider using Object.create(null) for data objects that will be merged with user input
• Implement a Content Security Policy that restricts dynamic code execution in browser environments

# Update y18n to patched version
npm update y18n

# Verify installed version is patched
npm list y18n

# Audit for additional vulnerabilities
npm audit