CVE-2021-21173 in Edge
Summary
by MITRE • 03/10/2021
Side-channel information leakage in Network Internals in Google Chrome prior to 89.0.4389.72 allowed a remote attacker to leak cross-origin data via a crafted HTML page.
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Analysis
by VulDB Data Team • 03/29/2021
The vulnerability identified as CVE-2021-21173 represents a significant side-channel information leakage issue within Google Chrome's network internals that existed prior to version 89.0.4389.72. This flaw exploited the browser's handling of cross-origin data transmission and allowed remote attackers to extract sensitive information from different origins through carefully crafted HTML pages. The vulnerability specifically targeted the network layer components that manage communication between browser processes and external resources, creating an avenue for unauthorized data exfiltration that bypassed traditional security boundaries.
The technical implementation of this vulnerability stems from insufficient isolation mechanisms within Chrome's network stack that process cross-origin requests. Attackers could construct malicious HTML pages containing specific network operations that would trigger information leakage through side-channel mechanisms. These side-channel attacks exploit timing variations, memory access patterns, or other indirect information flows that reveal data about the underlying system state. The flaw essentially allowed attackers to infer cross-origin data by observing the behavior of network operations and their associated timing characteristics, creating a covert channel for information extraction.
The operational impact of CVE-2021-21173 extends beyond simple data leakage, as it represents a fundamental breach in the browser's security model for handling cross-origin communications. Remote attackers could leverage this vulnerability to gather sensitive information from other origins without direct access to those resources, potentially compromising user privacy and system security. The attack vector through crafted HTML pages makes this vulnerability particularly dangerous as it requires no special privileges or user interaction beyond visiting a malicious website, enabling widespread exploitation across various user bases. This type of vulnerability directly impacts the browser's ability to maintain secure isolation between different origins, undermining core web security principles.
This vulnerability maps to CWE-203: "Information Leakage" and aligns with several ATT&CK techniques including T1071.004: "Application Layer Protocol: DNS" and T1566: "Phishing". The side-channel nature of the attack demonstrates how modern browsers must account for indirect information flows that can reveal sensitive data through seemingly benign operations. Mitigation strategies include upgrading to Chrome version 89.0.4389.72 or later, which implements proper isolation mechanisms and network operation handling. Organizations should also consider implementing additional network monitoring to detect unusual timing patterns that might indicate exploitation attempts. Browser vendors should continue to strengthen their isolation models and regularly audit network internals for similar side-channel vulnerabilities. The incident highlights the importance of comprehensive security testing that includes analysis of indirect information flows and side-channel attack vectors in complex software systems.