CVE-2021-21209 in Chrome
Summary
by MITRE • 04/26/2021
Inappropriate implementation in storage in Google Chrome prior to 90.0.4430.72 allowed a remote attacker to leak cross-origin data via a crafted HTML page.
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Analysis
by VulDB Data Team • 04/30/2021
The vulnerability identified as CVE-2021-21209 represents a critical security flaw in Google Chrome's storage implementation that existed prior to version 90.0.4430.72. This issue stems from an inadequate handling of cross-origin data isolation mechanisms within the browser's storage subsystem, creating a pathway for malicious actors to exploit the weakness through crafted web content. The vulnerability specifically targets the browser's ability to maintain proper separation between different origins when storing and retrieving data, which forms a fundamental pillar of web security architecture.
The technical implementation flaw manifests in how Chrome processes storage operations across different origins, allowing an attacker to construct a malicious HTML page that can access or retrieve data from other origins that should normally be isolated. This cross-origin data leakage occurs through improper validation of storage access requests, where the browser fails to adequately enforce the same-origin policy that typically prevents such unauthorized data access. The vulnerability operates at the intersection of web storage APIs and origin isolation mechanisms, exploiting a gap in Chrome's security model that should have prevented such cross-origin data exposure.
The operational impact of this vulnerability extends beyond simple data leakage, as it can enable sophisticated attacks such as cross-site scripting exploitation, session hijacking, and credential theft. Attackers can leverage this flaw to gather sensitive information from users' browsing sessions, potentially including cookies, local storage data, and other origin-specific information that could be used for further exploitation. The remote nature of the attack means that victims need only visit a malicious webpage to be compromised, making this vulnerability particularly dangerous in phishing campaigns or drive-by download scenarios. This type of vulnerability directly violates the core security principle of origin isolation that browsers enforce to protect user privacy and data integrity.
Mitigation strategies for CVE-2021-21209 require immediate patching of affected Chrome versions to the recommended build 90.0.4430.72 or later, which incorporates proper storage isolation mechanisms. Organizations should implement comprehensive browser update policies and consider using automated patch management systems to ensure all endpoints remain protected. Additionally, security teams should monitor for indicators of compromise related to this vulnerability and implement web application firewalls that can detect and block malicious HTML content attempting to exploit storage-related flaws. The vulnerability aligns with CWE-200 (Information Exposure) and can be mapped to ATT&CK technique T1213 (Data from Information Repositories) in threat modeling frameworks, emphasizing the need for layered security approaches that address both browser-level and network-level protections.
This vulnerability demonstrates the critical importance of proper storage implementation in web browsers and highlights the ongoing challenges in maintaining secure cross-origin isolation. The flaw represents a failure in Chrome's security model that could have been prevented through more rigorous testing of storage access controls and better adherence to established security practices. Security researchers should continue monitoring for similar implementation gaps in storage APIs, as these types of vulnerabilities often remain undetected for extended periods due to their subtle nature and the complexity of modern web storage systems.