CVE-2009-4027 in Linux
Summary
by MITRE
Race condition in the mac80211 subsystem in the Linux kernel before 2.6.32-rc8-next-20091201 allows remote attackers to cause a denial of service (system crash) via a Delete Block ACK (aka DELBA) packet that triggers a certain state change in the absence of an aggregation session.
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Analysis
by VulDB Data Team • 08/28/2021
The vulnerability described in CVE-2009-4027 represents a critical race condition within the mac80211 wireless networking subsystem of the Linux kernel. This flaw specifically affects systems running kernel versions prior to 2.6.32-rc8-next-20091201 and manifests as a denial of service condition that can lead to complete system crashes. The vulnerability operates within the IEEE 802.11 wireless networking framework where the mac80211 subsystem manages wireless device drivers and handles various wireless communication protocols including block acknowledgment mechanisms. The race condition occurs during the processing of Delete Block ACK (DELBA) frames which are used to terminate wireless block acknowledgment sessions in high-throughput wireless networks. When a malicious remote attacker crafts and transmits a specially formatted DELBA packet, the system's handling of this frame triggers an improper state transition within the wireless subsystem's aggregation session management logic.
The technical exploitation of this vulnerability relies on the timing-dependent nature of the race condition within the kernel's wireless networking code path. The mac80211 subsystem maintains internal state information about active wireless aggregation sessions, and the DELBA packet processing routine contains a flaw where the system fails to properly validate or synchronize access to these session state variables. When the system receives a DELBA packet without an active aggregation session, the race condition allows for a memory access violation or invalid state transition that results in a kernel panic. This particular vulnerability falls under the CWE-362 category of "Concurrent Execution using Shared Resource with Improper Synchronization" and demonstrates how improper locking mechanisms can lead to critical system instability. The flaw is particularly dangerous because it requires no local privileges or authentication to exploit, making it a remote attack vector that can be leveraged by any attacker within wireless range of the vulnerable system.
The operational impact of CVE-2009-4027 extends beyond simple denial of service to potentially compromise the availability of wireless networking services on affected systems. In enterprise environments where wireless infrastructure is critical for operations, this vulnerability could lead to significant service disruption, particularly in scenarios involving wireless access points, routers, or client devices that rely on the mac80211 subsystem for wireless communication. The vulnerability affects wireless networking functionality across multiple device types including laptops, smartphones, and wireless access points running Linux-based operating systems. Attackers could exploit this vulnerability to repeatedly crash wireless services, effectively rendering wireless connectivity unavailable to legitimate users. The impact is further amplified when considering that many wireless networking devices in enterprise and consumer environments are not regularly updated, making them vulnerable to this and similar race condition exploits. From an ATT&CK framework perspective, this vulnerability maps to the T1499.004 technique of "Network Denial of Service" and represents a critical weakness in the system's network infrastructure layer that could be leveraged as part of broader attack campaigns targeting wireless network availability.
The mitigation strategy for this vulnerability primarily involves immediate kernel version upgrades to 2.6.32-rc8-next-20091201 or later, which contain the necessary patches to address the race condition in the mac80211 subsystem. System administrators should prioritize updating wireless networking components and ensure that all devices running Linux-based wireless networking stacks receive the appropriate kernel security patches. Additionally, network administrators can implement temporary mitigations such as disabling wireless block acknowledgment features or implementing network segmentation to limit the potential impact of exploitation. Organizations should also consider monitoring wireless network traffic for unusual DELBA packet patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper synchronization mechanisms in kernel code and underscores the need for comprehensive testing of concurrent execution paths in networking subsystems. Given the nature of the flaw, regular security audits of kernel networking components and adherence to security update schedules are essential for maintaining wireless network availability and preventing exploitation of similar race condition vulnerabilities in the future.