CVE-2016-4656 in iOS
Summary
by MITRE
The kernel in Apple iOS before 9.3.5 allows attackers to execute arbitrary code in a privileged context or cause a denial of service (memory corruption) via a crafted app.
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Analysis
by VulDB Data Team • 01/29/2025
The vulnerability identified as CVE-2016-4656 represents a critical kernel-level flaw in Apple iOS versions prior to 9.3.5 that enables attackers to escalate privileges and execute arbitrary code within the operating system's most privileged execution context. This vulnerability resides within the kernel subsystem, which operates at the highest privilege level and manages core system resources including memory management, process scheduling, and hardware access controls. The flaw allows malicious applications to leverage kernel memory corruption to gain unauthorized access to system resources that should normally be restricted to the operating system itself. The vulnerability's impact extends beyond simple privilege escalation as it can also result in denial of service conditions that may cause system instability or complete system crashes.
The technical nature of this vulnerability stems from improper input validation and memory management within the iOS kernel components. Attackers can craft malicious applications that exploit buffer overflows or other memory corruption mechanisms to manipulate kernel data structures and execute code with kernel-level privileges. This type of vulnerability falls under the CWE-125 weakness category, which encompasses out-of-bounds read errors that can lead to memory corruption and privilege escalation. The kernel's memory management subsystem fails to properly validate input parameters from user-space applications, allowing crafted payloads to overwrite critical kernel memory regions. The vulnerability demonstrates a classic example of a kernel exploit that leverages the trust relationship between user applications and kernel services, enabling attackers to bypass the operating system's security model and execute code with the highest possible privileges.
The operational impact of CVE-2016-4656 is severe and multifaceted, affecting all iOS devices running versions below 9.3.5 including iPhones, iPads, and iPod touches. Attackers can exploit this vulnerability through seemingly legitimate applications downloaded from the App Store or through malicious applications distributed through other channels. Once exploited, the vulnerability allows attackers to gain complete control over the device, enabling them to access all user data, install additional malicious software, monitor communications, and potentially use the compromised device as a pivot point for attacking other systems. The vulnerability also creates potential for denial of service scenarios that can render devices unusable, causing significant disruption to users and enterprises. Organizations relying on iOS devices for business operations face elevated risks as this vulnerability can be leveraged for data exfiltration, corporate espionage, and disruption of critical business processes. The vulnerability's exploitation does not require physical access to the device, making it particularly dangerous as attackers can compromise devices remotely through malicious applications.
Mitigation strategies for this vulnerability primarily focus on immediate system updates and security hardening measures. Apple addressed this issue through the iOS 9.3.5 update, which included kernel memory management patches and input validation improvements that prevent the exploitation techniques used to trigger the vulnerability. Organizations should implement immediate patch management policies to ensure all iOS devices receive the latest security updates, as the vulnerability remains exploitable in older iOS versions. Additional protective measures include implementing mobile device management solutions that can enforce security policies, monitoring for suspicious application behavior, and conducting regular security assessments of iOS devices within the organization. Network-level protections such as application whitelisting and sandboxing measures can provide additional defense-in-depth layers. The vulnerability's remediation aligns with ATT&CK framework technique T1068 which covers 'Exploitation for Privilege Escalation' and T1489 which covers 'Service Stop', demonstrating how kernel-level vulnerabilities can be exploited to achieve both privilege escalation and system disruption objectives. Security teams should also consider implementing endpoint detection and response solutions that can identify anomalous behavior patterns consistent with kernel exploitation attempts, as these vulnerabilities often leave detectable traces in system logs and memory forensic analysis.