CVE-2020-7774 in y18n
Summary
by MITRE • 11/17/2020
This affects the package y18n before 5.0.5. PoC by po6ix: const y18n = require('y18n')(); y18n.setLocale('__proto__'); y18n.updateLocale({polluted: true}); console.log(polluted); // true
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 12/08/2020
The vulnerability identified as CVE-2020-7774 affects the y18n internationalization package version prior to 5.0.5, representing a prototype pollution security flaw that can be exploited to manipulate object prototypes within JavaScript applications. This issue stems from the package's inadequate handling of locale settings, specifically when the setLocale method is invoked with the special string '_proto_' as a parameter. The vulnerability allows attackers to inject malicious properties into the Object.prototype, which can subsequently be accessed by any code that relies on standard JavaScript object traversal mechanisms. The proof of concept demonstrates how an attacker can exploit this weakness by first setting the locale to '_proto_', then updating the locale with a polluted object containing arbitrary properties, ultimately resulting in the pollution of the global prototype chain.
The technical implementation of this vulnerability resides in the package's failure to properly validate input parameters during the locale setting process. When the setLocale method accepts '_proto_' as a valid locale identifier, it bypasses normal validation checks and directly assigns this value to an internal prototype property. The subsequent updateLocale call then propagates malicious data into the prototype chain, effectively polluting the Object.prototype with attacker-controlled properties. This flaw aligns with CWE-471, which categorizes improper protection against prototype pollution, and represents a direct exploitation of JavaScript's prototype inheritance mechanism. The vulnerability operates at the application level rather than at the system level, making it particularly dangerous as it can affect any JavaScript runtime environment where the vulnerable package is utilized.
The operational impact of CVE-2020-7774 extends beyond simple prototype pollution, potentially enabling attackers to manipulate application behavior, bypass security controls, or even execute arbitrary code in certain contexts. When the prototype chain is polluted, any code that iterates over object properties or relies on standard JavaScript object methods may inadvertently access or execute the malicious properties injected into the prototype. This can lead to unexpected application behavior, data corruption, or more serious consequences such as privilege escalation in applications that rely on prototype-based access controls. The vulnerability is particularly concerning in Node.js environments where the y18n package is commonly used for internationalization, as it can affect web applications, command-line tools, and server-side applications that depend on proper object isolation. According to ATT&CK framework category T1190, this vulnerability represents a technique for exploiting weaknesses in application logic to achieve unauthorized code execution or data manipulation.
Mitigation strategies for this vulnerability require immediate patching of the y18n package to version 5.0.5 or later, which includes proper input validation and prototype chain protection mechanisms. Organizations should conduct comprehensive vulnerability assessments to identify all applications and systems utilizing vulnerable versions of the package, particularly in environments where internationalization features are employed. Additionally, implementing runtime protections such as prototype validation checks, input sanitization for locale parameters, and monitoring for unusual object property access patterns can provide additional layers of defense. Security teams should also consider implementing dependency scanning tools that can automatically detect vulnerable package versions and alert administrators to potential exposure. The fix implemented in the patched version typically involves validating that locale identifiers do not correspond to reserved JavaScript prototype properties and ensuring that object property assignments maintain proper isolation from the global prototype chain.