CVE-2016-4590 in iOS
Summary
by MITRE
WebKit in Apple iOS before 9.3.3 and Safari before 9.1.2 mishandles about: URLs, which allows remote attackers to bypass the Same Origin Policy via a crafted web site.
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Analysis
by VulDB Data Team • 09/05/2022
The vulnerability identified as CVE-2016-4590 represents a critical security flaw in Apple's WebKit rendering engine that affected iOS versions prior to 9.3.3 and Safari versions before 9.1.2. This issue stems from improper handling of about: URLs within the web browser's architecture, creating a significant bypass mechanism for the fundamental Same Origin Policy that governs web security. The Same Origin Policy serves as a cornerstone of web security by preventing scripts from one origin from accessing resources from another origin, thereby protecting users from cross-site scripting attacks and data theft. When this policy is circumvented, it opens pathways for malicious actors to execute unauthorized operations across different domains.
The technical flaw manifests specifically in how WebKit processes about: URLs, which are special URLs used by web browsers to access internal browser functionality and information. These URLs typically provide access to browser-specific resources and are designed to operate within strict security boundaries. The vulnerability occurs because the WebKit engine fails to properly validate or restrict access to these internal resources when they are accessed through crafted web pages. Attackers can exploit this by constructing malicious websites that utilize about: URLs in ways that bypass normal security restrictions, effectively allowing them to access or manipulate resources that should remain isolated from external web content.
The operational impact of this vulnerability extends beyond simple privilege escalation, creating a comprehensive attack surface that enables sophisticated exploitation techniques. Remote attackers can leverage this flaw to perform cross-origin resource access, potentially gaining access to sensitive user data, cookies, or other browser resources that should be protected by the Same Origin Policy. This vulnerability aligns with CWE-284, which addresses improper access control, and represents a significant weakness in the browser's security model. The attack vector is particularly dangerous because it operates entirely through web-based means, requiring no local system compromise or additional privileges from the attacker. The vulnerability essentially allows attackers to craft web pages that can access internal browser components, potentially enabling data exfiltration, session hijacking, or further exploitation of other browser vulnerabilities.
Mitigation strategies for CVE-2016-4590 primarily focus on immediate system updates and security patches provided by Apple. The most effective remediation involves updating to iOS 9.3.3 or later versions and Safari 9.1.2 or later, which contain the necessary code modifications to properly handle about: URLs and restore proper Same Origin Policy enforcement. Security administrators should also implement additional protective measures such as web application firewalls, content security policies, and browser hardening configurations to reduce the attack surface. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and defense evasion, as attackers can use it to bypass security controls that would normally protect against cross-site attacks. Organizations should also consider network-level monitoring to detect suspicious patterns of about: URL usage and implement regular security assessments to identify potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation and secure handling of internal browser resources, emphasizing that even seemingly benign URL schemes can create significant security risks when not properly managed within web browser security models.