CVE-2016-6828 in Android
Summary
by MITRE
The tcp_check_send_head function in include/net/tcp.h in the Linux kernel before 4.7.5 does not properly maintain certain SACK state after a failed data copy, which allows local users to cause a denial of service (tcp_xmit_retransmit_queue use-after-free and system crash) via a crafted SACK option.
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Analysis
by VulDB Data Team • 10/05/2024
The vulnerability described in CVE-2016-6828 represents a critical flaw in the Linux kernel's TCP implementation that affects versions prior to 4.7.5. This issue resides within the tcp_check_send_head function located in the include/net/tcp.h file, which is part of the kernel's networking stack responsible for managing TCP connections and data transmission. The vulnerability specifically targets the handling of Selective Acknowledgment (SACK) state management during TCP data transmission operations, creating a scenario where improper state maintenance can lead to severe system instability.
The technical root cause of this vulnerability stems from the failure to properly maintain SACK state information when a data copy operation fails during TCP transmission. When a TCP segment is transmitted and subsequently fails to copy data properly, the kernel's tcp_check_send_head function does not correctly update the SACK state variables that track which segments have been successfully transmitted and acknowledged. This improper state management creates a condition where the kernel continues to reference memory locations that may have been freed or reallocated, leading to use-after-free conditions that are particularly dangerous in kernel space operations.
The operational impact of this vulnerability is significant and manifests as a local denial of service condition that can result in complete system crashes. Attackers with local access to a system can exploit this vulnerability by crafting specific SACK options that trigger the flawed code path in the TCP stack. When the vulnerable kernel processes these crafted SACK options, it executes the use-after-free condition in the tcp_xmit_retransmit_queue function, causing the kernel to attempt to access freed memory locations. This memory corruption typically results in kernel oops messages, system panics, and ultimately complete system crashes that require manual reboot to restore normal operation.
This vulnerability aligns with CWE-416, which describes the use of freed memory condition, and demonstrates how improper memory management in kernel space can lead to catastrophic system failures. The attack vector is classified as local privilege escalation since an attacker must already have access to the system to exploit this vulnerability, but the impact is severe enough to justify immediate patching. From an ATT&CK framework perspective, this vulnerability could be categorized under T1063 for rootkit detection and T1499 for network denial of service, though it primarily represents a system stability compromise rather than a direct attack on network services.
The mitigation strategy for this vulnerability involves upgrading to Linux kernel version 4.7.5 or later, where the tcp_check_send_head function has been corrected to properly maintain SACK state information during data copy failures. System administrators should prioritize patching this vulnerability across all systems running affected kernel versions, particularly servers and critical infrastructure where availability is paramount. Additionally, monitoring for kernel oops messages and system crashes that may indicate exploitation attempts can provide early warning signs of potential attacks. Organizations should also consider implementing kernel hardening measures and maintaining up-to-date security patches as part of their overall security posture to prevent similar vulnerabilities from compromising system availability and stability.