CVE-2016-1864 in tvOS
Summary
by MITRE
The XSS auditor in WebKit, as used in Apple iOS before 9.3 and Safari before 9.1, does not properly handle redirects in block mode, which allows remote attackers to obtain sensitive information via a crafted URL.
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Analysis
by VulDB Data Team • 09/30/2024
The vulnerability identified as CVE-2016-1864 resides within the WebKit rendering engine's cross-site scripting auditor component, specifically affecting Apple iOS versions prior to 9.3 and Safari versions before 9.1. This flaw represents a critical security oversight in the browser's defensive mechanisms designed to prevent malicious script execution. The XSS auditor serves as a protective layer that monitors and blocks potentially harmful cross-site scripting attempts by analyzing URLs and request patterns. However, the implementation contained a significant gap in its redirect handling logic that undermines its effectiveness in blocking malicious content.
The technical flaw manifests when the XSS auditor operates in block mode, which is the default security configuration designed to actively prevent script execution. During redirect operations, the auditor fails to properly validate or sanitize the redirected URLs, creating a pathway for attackers to bypass the security controls. This occurs because the system does not adequately verify the destination of redirects before allowing the navigation to proceed, particularly when the redirect chain involves multiple hops or complex URL structures. The vulnerability exploits the gap between the initial URL analysis and the final navigation execution, allowing malicious actors to craft URLs that appear benign during initial inspection but redirect to malicious endpoints.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables attackers to circumvent the browser's built-in security mechanisms. Remote attackers can construct malicious URLs that initially pass the XSS auditor's scrutiny but subsequently redirect users to sites hosting malicious content or phishing pages. This allows for sophisticated attacks including credential theft, session hijacking, and the delivery of additional malware through the compromised browser session. The vulnerability particularly affects users of older iOS and Safari versions where the security updates had not yet been deployed, leaving them exposed to targeted attacks that exploit this specific flaw in the redirect handling process.
This vulnerability maps directly to CWE-79, which describes cross-site scripting flaws in web applications, and specifically relates to CWE-20, representing improper input validation. The issue also aligns with ATT&CK technique T1059.001, which covers command and scripting interpreter usage, as attackers can leverage this vulnerability to execute malicious scripts through compromised browser sessions. The flaw demonstrates a classic case of incomplete security controls where defensive mechanisms fail to account for all possible attack vectors, particularly those involving redirect chains that are common in modern web applications. Organizations and users affected by this vulnerability must prioritize immediate remediation through system updates and security patches to prevent exploitation of this bypass mechanism.
The broader implications highlight the complexity of modern web security implementations where defensive layers must account for sophisticated attack patterns including redirect manipulation. This vulnerability underscores the importance of comprehensive testing of security controls under various operational conditions, particularly those involving complex URL handling scenarios. The flaw serves as a reminder that even well-integrated security features can contain implementation gaps that attackers can exploit through careful analysis of the system's behavior under specific conditions. Security teams should implement monitoring for suspicious redirect patterns and ensure that all browser and operating system components receive timely updates to protect against similar vulnerabilities in the future.