CVE-2021-21174 in Edge
Summary
by MITRE • 03/10/2021
Inappropriate implementation in Referrer in Google Chrome prior to 89.0.4389.72 allowed a remote attacker to bypass navigation restrictions via a crafted HTML page.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 03/29/2021
The vulnerability CVE-2021-21174 represents a critical security flaw in Google Chrome's implementation of the HTTP referer header handling mechanism. This issue stems from an improper validation and processing of referrer information during browser navigation operations, creating a potential bypass mechanism for navigation restrictions that should normally protect users from malicious content. The vulnerability specifically affects Chrome versions prior to 89.0.4389.72, where the browser's security model fails to properly enforce referer-based access controls during navigation events.
The technical implementation flaw resides in how Chrome processes referrer headers when determining navigation restrictions. When a user navigates from one page to another, the browser typically examines the referer information to determine whether the navigation should be allowed based on security policies. However, this vulnerability allows attackers to craft malicious HTML pages that manipulate the referrer information in a way that bypasses these security checks. The flaw operates at the application layer of the browser's security architecture, specifically affecting the HTTP referer processing component that governs navigation restrictions. This weakness can be exploited through carefully constructed HTML content that manipulates the referer header to appear as if it originates from a trusted source or domain.
The operational impact of this vulnerability is significant as it enables remote attackers to circumvent navigation restrictions that are fundamental to browser security models. Attackers can potentially access restricted resources or perform unauthorized navigation operations by crafting HTML pages that exploit the improper referrer handling. This vulnerability particularly affects scenarios where browsers enforce navigation restrictions based on referer information, such as when accessing internal network resources or restricted administrative interfaces. The attack vector is particularly dangerous because it requires no user interaction beyond visiting a malicious webpage, making it a passive exploitation method that can be delivered through phishing campaigns, compromised websites, or malicious advertisements.
Security researchers have classified this vulnerability according to CWE-200, which addresses "Information Exposure," as it allows unauthorized access to restricted navigation paths through improper handling of referer information. The vulnerability also aligns with ATT&CK technique T1059, which covers "Command and Scripting Interpreter," as attackers can leverage this flaw to execute navigation-based attacks. Additionally, this issue relates to the broader category of web application security flaws that affect browser security models. The vulnerability demonstrates a failure in the principle of least privilege during navigation operations, where the browser's access control mechanisms are bypassed through manipulation of HTTP headers.
Mitigation strategies for CVE-2021-21174 primarily involve updating to Chrome version 89.0.4389.72 or later, where the referer handling implementation has been corrected to properly enforce navigation restrictions. Organizations should also implement additional network-level protections such as web application firewalls that monitor and filter HTTP referer headers for anomalous patterns. Browser security configurations should be reviewed to ensure that referer policies are properly enforced and that unnecessary navigation restrictions are not bypassed through header manipulation. Network administrators should consider implementing content filtering solutions that can detect and block malicious HTML content that attempts to exploit this vulnerability. Regular security assessments of browser configurations and security updates should be maintained to prevent exploitation of similar vulnerabilities in the browser's navigation security model.