CVE-2020-8910 in Closure Library
Summary
by MITRE
A URL parsing issue in goog.uri of the Google Closure Library versions up to and including v20200224 allows an attacker to send malicious URLs to be parsed by the library and return the wrong authority. Mitigation: update your library to version v20200315.
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Analysis
by VulDB Data Team • 05/10/2025
The vulnerability identified as CVE-2020-8910 resides within the Google Closure Library's URL parsing functionality, specifically affecting the goog.uri component. This issue represents a critical flaw in how the library processes and interprets Uniform Resource Locators, potentially allowing attackers to manipulate URL structures in ways that could compromise application security. The vulnerability impacts all versions of the Google Closure Library up to and including version v20200224, making it a widespread concern for developers who rely on this popular JavaScript library for web application development and URL manipulation.
The technical flaw manifests in the URL parsing algorithm where the goog.uri component fails to correctly identify and extract the authority component of maliciously crafted URLs. This occurs when the library encounters specially constructed URLs that exploit parsing ambiguities in the URI specification, particularly around the handling of special characters, encoding sequences, and edge cases in URL structure. The vulnerability stems from insufficient validation and proper parsing of URL components, allowing an attacker to craft URLs that, when processed by the library, return incorrect authority information. This misinterpretation can lead to various security implications including potential redirection attacks, cross-site scripting vulnerabilities, and unauthorized access to resources.
The operational impact of this vulnerability extends beyond simple URL parsing errors, as it can be leveraged in several attack vectors within web applications that utilize the Google Closure Library. When applications process user-supplied URLs through the affected library, attackers can manipulate the parsed authority component to redirect users to malicious sites, inject malicious content, or bypass security controls that depend on correct URL parsing. This vulnerability particularly affects web applications that dynamically construct URLs, perform URL validation, or implement security measures based on URL components. The flaw creates a potential pathway for attackers to circumvent security mechanisms that rely on proper URL parsing and authorization checks.
Security professionals should note that this vulnerability aligns with CWE-154, which addresses improper handling of URL parsing in web applications, and can be categorized under ATT&CK technique T1071.004 for application layer protocol manipulation. The recommended mitigation strategy involves updating to version v20200315 of the Google Closure Library, which includes corrected URL parsing logic that properly handles edge cases and malicious URL constructs. Organizations should conduct thorough testing of their applications after implementing this update to ensure no regressions occur in URL handling functionality while gaining protection against the specific parsing vulnerability.
The broader implications of this vulnerability highlight the critical importance of proper URL validation and parsing in web security architectures. Given the widespread adoption of the Google Closure Library across numerous web applications and frameworks, this vulnerability demonstrates how seemingly minor parsing flaws can have significant security consequences. The issue underscores the necessity for comprehensive testing of third-party libraries and regular security updates to maintain robust application defenses against evolving threats in the cybersecurity landscape.