CVE-2011-3259 in iOS
Summary
by MITRE
The kernel in Apple iOS before 5 and Apple TV before 4.4 does not properly recover memory allocated for incomplete TCP connections, which allows remote attackers to cause a denial of service (resource consumption) by making many connection attempts.
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Analysis
by VulDB Data Team • 11/24/2021
The vulnerability described in CVE-2011-3259 represents a critical memory management flaw within the kernel implementation of Apple iOS versions prior to 5.0 and Apple TV versions prior to 4.4. This issue stems from improper handling of memory allocation during TCP connection establishment processes, specifically when connections are terminated prematurely or fail to complete successfully. The flaw manifests as a failure to properly release memory resources that were allocated for incomplete TCP connection states, creating a condition where memory fragments remain allocated even after the connection attempt has concluded. This memory leakage occurs at the kernel level, affecting the core networking stack that handles all network communication on these devices.
The technical exploitation of this vulnerability involves remote attackers initiating numerous TCP connection attempts to target systems running the affected software versions. Each failed or incomplete connection attempt results in memory allocation that is not properly deallocated, leading to progressive memory consumption over time. As attackers continue to make connection attempts, the cumulative effect of these memory leaks causes the system to gradually consume available memory resources until the device becomes unresponsive or crashes entirely. The vulnerability operates at the transport layer of the network stack, specifically targeting the Transmission Control Protocol implementation within the kernel's networking subsystem. This type of memory exhaustion attack directly violates the principle of resource management and can be classified under CWE-400, which addresses "Uncontrolled Resource Consumption" in software systems.
The operational impact of this vulnerability extends beyond simple denial of service, as it can render affected devices completely unusable and potentially compromise the overall security posture of systems running these outdated software versions. When memory consumption reaches critical levels, the operating system may become unstable, leading to unexpected reboots, application crashes, or complete system lockups that prevent normal device operation. The vulnerability is particularly concerning because it can be exploited remotely without requiring authentication or specialized privileges, making it accessible to any attacker with network access to the target device. This characteristic aligns with ATT&CK technique T1499.001, which covers "Network Denial of Service" attacks, and demonstrates how improper resource handling can be weaponized for system disruption. The memory leak behavior creates a persistent degradation of system performance that can be difficult to detect and remediate, as the symptoms may not immediately appear until significant resource consumption has occurred.
Mitigation strategies for this vulnerability require immediate software updates to the affected Apple iOS and Apple TV versions, as the fix involves proper memory deallocation mechanisms for incomplete TCP connections within the kernel networking stack. System administrators should prioritize patching affected devices and implement network monitoring to detect unusual connection patterns that might indicate exploitation attempts. Additionally, implementing rate limiting and connection throttling mechanisms at network boundaries can help reduce the impact of such attacks by limiting the number of connection attempts that can be made within a given time period. The vulnerability highlights the importance of proper memory management in kernel-level code and serves as a reminder of the critical need for robust resource handling practices in operating system implementations. Organizations should also consider implementing intrusion detection systems that can identify and alert on patterns consistent with TCP connection exhaustion attacks, while maintaining up-to-date security patches and conducting regular vulnerability assessments to identify similar memory management issues in other system components.