CVE-2016-1784 in iOS
Summary
by MITRE
The History implementation in WebKit in Apple iOS before 9.3, Safari before 9.1, and tvOS before 9.2 allows remote attackers to cause a denial of service (resource consumption and application crash) via a crafted web site.
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Analysis
by VulDB Data Team • 07/11/2022
The vulnerability identified as CVE-2016-1784 resides within the History implementation component of WebKit engine used in Apple's mobile and desktop operating systems. This flaw affects iOS versions prior to 9.3, Safari versions before 9.1, and tvOS versions before 9.2, representing a significant security gap that could be exploited by remote attackers to disrupt normal system operations. The vulnerability specifically targets the web browser's history management functionality, which is a fundamental component responsible for tracking user navigation and maintaining browsing records. The issue manifests when malicious websites craft specific web content that triggers abnormal behavior in the history handling mechanisms, leading to resource exhaustion and application instability. This type of vulnerability falls under the category of resource exhaustion attacks where attacker-controlled input causes the system to consume excessive memory or processing power, ultimately resulting in application crashes and denial of service conditions. The exploitation scenario involves a remote attacker who can deliver malicious web content through various attack vectors including phishing websites, compromised web pages, or malicious advertisements that when loaded in the affected browsers trigger the vulnerable history implementation.
The technical flaw stems from inadequate input validation and memory management within the WebKit History API implementation. When processing specially crafted web content that manipulates the browser's history stack, the system fails to properly handle boundary conditions and excessive data manipulation, leading to uncontrolled resource consumption. This vulnerability can be classified as a CWE-400 category issue, specifically related to resource management flaws where the system does not properly limit or control the consumption of system resources. The flaw operates by exploiting the way the browser handles history entries and navigation events, particularly when dealing with malformed or excessively complex history data structures. Attackers can construct web pages that create an excessive number of history entries or manipulate existing entries in ways that cause the browser engine to allocate disproportionate amounts of memory or processing cycles. The vulnerability demonstrates a classic case of insufficient bounds checking and memory allocation controls that are essential for maintaining system stability and preventing resource exhaustion attacks. The implementation lacks proper safeguards to detect and prevent abnormal history manipulation patterns that could lead to system instability.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise the overall user experience and system security posture. When exploited, the vulnerability can cause affected browsers to become unresponsive, crash entirely, or consume excessive system resources, forcing users to restart applications or devices to restore normal functionality. This disruption affects not only individual user sessions but can also impact system performance and availability, particularly in environments where multiple users access the same affected systems. The vulnerability's remote nature means that exploitation does not require physical access or local privileges, making it particularly dangerous as attackers can target users from anywhere on the internet. From an attacker's perspective, this vulnerability provides a low-effort method to disrupt services, making it attractive for both casual attackers seeking to cause inconvenience and more sophisticated threat actors looking to establish persistent access through service disruption as a precursor to more advanced attacks. The vulnerability also aligns with ATT&CK technique T1499.004, which involves network denial of service attacks through resource exhaustion, demonstrating how this flaw can be leveraged in broader attack frameworks.
Mitigation strategies for CVE-2016-1784 primarily focus on immediate system updates and patches provided by Apple to address the underlying WebKit implementation issues. Users should promptly install the latest security updates for their operating systems, including iOS 9.3, Safari 9.1, and tvOS 9.2 releases that contain fixes for this vulnerability. System administrators should implement proactive monitoring to detect potential exploitation attempts and ensure all affected devices are updated to patched versions. Network security controls can include web filtering solutions that block access to known malicious domains and content that might trigger this vulnerability. The patching approach addresses the root cause by implementing proper input validation, bounds checking, and resource management controls within the WebKit History API implementation. Organizations should also consider implementing browser hardening measures that limit the exposure of vulnerable components and establish monitoring protocols to detect abnormal resource consumption patterns that might indicate exploitation attempts. Additionally, users should maintain awareness of phishing attempts and avoid visiting untrusted websites, as these remain the primary delivery mechanism for exploiting this vulnerability. The fix typically involves implementing stricter memory allocation limits and enhanced validation routines for history manipulation operations, preventing the excessive resource consumption that leads to application crashes and denial of service conditions.