CVE-2021-21135 in Chrome
Summary
by MITRE • 02/09/2021
Inappropriate implementation in Performance API in Google Chrome prior to 88.0.4324.96 allowed a remote attacker to leak cross-origin data via a crafted HTML page.
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Analysis
by VulDB Data Team • 02/26/2021
The vulnerability CVE-2021-21135 represents a critical security flaw in Google Chrome's Performance API implementation that existed prior to version 88.0.4324.96. This issue falls under the category of information disclosure vulnerabilities and specifically targets the browser's performance monitoring capabilities. The flaw allows remote attackers to exploit cross-origin data leakage through carefully crafted HTML pages, potentially compromising user privacy and system security. The vulnerability stems from improper handling of performance data across different origins, creating an avenue for malicious actors to gather sensitive information from unrelated websites.
The technical implementation flaw resides in how Chrome's Performance API manages cross-origin resource access and data collection. When websites attempt to access performance metrics through the API, the browser fails to properly enforce same-origin policies, enabling unauthorized data retrieval from other domains. This misimplementation allows attackers to construct malicious web pages that can access performance timing data from cross-origin resources, effectively bypassing security boundaries that should prevent such information leakage. The vulnerability is particularly dangerous because it operates at the browser level, leveraging legitimate performance monitoring APIs to achieve unauthorized data access.
The operational impact of this vulnerability extends beyond simple information disclosure, creating potential risks for user privacy and application security. Attackers can exploit this flaw to gather detailed timing information about user interactions across different websites, potentially enabling fingerprinting attacks that could track user behavior patterns. The cross-origin data leakage could reveal sensitive information about web application performance, user engagement patterns, and even underlying system characteristics. This vulnerability particularly affects users of older Chrome versions and could be leveraged in sophisticated phishing campaigns or advanced persistent threat operations where attackers seek to gather comprehensive intelligence about their targets.
Mitigation strategies for CVE-2021-21135 primarily focus on immediate browser updates and implementation of additional security controls. Organizations should prioritize updating Chrome installations to version 88.0.4324.96 or later to address the vulnerability. Security teams should also implement network-level monitoring to detect potential exploitation attempts and consider deploying web application firewalls that can block suspicious performance API access patterns. The vulnerability aligns with CWE-200, which addresses "Information Exposure," and maps to ATT&CK technique T1566 for social engineering, as attackers may use this vulnerability in conjunction with other reconnaissance activities to build detailed profiles of target users. Additional defensive measures include implementing strict content security policies and monitoring for unusual performance API usage patterns that could indicate exploitation attempts.