CVE-2016-1782 in iOS
Summary
by MITRE
WebKit in Apple iOS before 9.3 and Safari before 9.1 does not properly restrict redirects that specify a TCP port number, which allows remote attackers to bypass intended port restrictions via a crafted web site.
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Analysis
by VulDB Data Team • 07/11/2022
The vulnerability identified as CVE-2016-1782 resides within Apple WebKit engine components that power iOS Safari and other web browsing applications. This flaw represents a significant security oversight in how the browser handles HTTP redirect mechanisms, specifically concerning TCP port specifications. The vulnerability affects iOS versions prior to 9.3 and Safari versions before 9.1, indicating a prolonged period during which systems remained exposed to potential exploitation. The core issue manifests when WebKit processes redirects that explicitly define TCP port numbers, failing to properly validate or restrict these port specifications according to established security boundaries.
The technical implementation of this vulnerability stems from insufficient input validation within WebKit's redirect processing logic. When a web page attempts to redirect a user to a specific TCP port through an HTTP redirect header, the browser should enforce strict port restriction policies to prevent unauthorized access to system services. However, the flaw allows attackers to craft malicious websites that specify arbitrary port numbers in redirect URLs, bypassing the normal port restriction mechanisms that typically prevent access to privileged ports. This behavior creates a pathway for attackers to potentially exploit network services that should remain protected from external access.
The operational impact of this vulnerability extends beyond simple web browsing security concerns, as it enables attackers to circumvent fundamental network security controls. An attacker could construct a malicious web page that redirects users to a specific port on the local network, potentially accessing services that should only be accessible through internal network protocols or privileged access. This capability undermines the security model of web browsers and operating systems, as it allows for unauthorized port access through seemingly benign web navigation. The vulnerability particularly affects scenarios where network services are configured to operate on non-standard ports, creating potential exposure points for attacks targeting these specific ports.
From a cybersecurity perspective, this vulnerability aligns with CWE-20, which describes improper input validation, and represents a classic example of how inadequate security controls in application-level components can create significant attack vectors. The flaw provides attackers with a method to bypass network-level security restrictions that would normally prevent access to specific ports, effectively creating a backdoor through legitimate web browsing activities. This vulnerability also maps to ATT&CK technique T1071.001, which covers application layer protocol usage, as it exploits legitimate web protocols to achieve unauthorized access. Organizations and users should recognize that this vulnerability represents a fundamental flaw in how browser security boundaries are enforced, making it particularly dangerous in environments where network segmentation and port-based access controls are critical security measures.
Mitigation strategies for CVE-2016-1782 primarily focus on system updates and patch management. Apple addressed this vulnerability through iOS 9.3 and Safari 9.1 updates, which implemented proper validation of redirect port specifications and enforced stricter port restriction policies. Security administrators should prioritize immediate deployment of these updates across all affected systems to prevent exploitation. Additional protective measures include implementing network-level restrictions on web access, configuring firewalls to block suspicious redirect patterns, and monitoring network traffic for unusual port access attempts. Organizations should also consider implementing web application firewalls and content filtering solutions that can detect and block malicious redirect patterns. The vulnerability underscores the importance of maintaining current security patches and highlights the critical need for robust input validation in all network-facing applications to prevent similar issues from arising in the future.