CVE-2009-2844 in Linux
Summary
by MITRE
cfg80211 in net/wireless/scan.c in the Linux kernel 2.6.30-rc1 and other versions before 2.6.31-rc6 allows remote attackers to cause a denial of service (crash) via a sequence of beacon frames in which one frame omits an SSID Information Element (IE) and the subsequent frame contains an SSID IE, which triggers a NULL pointer dereference in the cmp_ies function. NOTE: a potential weakness in the is_mesh function was also addressed, but the relevant condition did not exist in the code, so it is not a vulnerability.
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability described in CVE-2009-2844 resides within the Linux kernel's wireless subsystem, specifically in the cfg80211 component responsible for managing wireless device configuration and scanning operations. This issue affects kernel versions prior to 2.6.31-rc6 and represents a classic denial of service vulnerability that can be exploited by remote attackers to crash wireless networking functionality. The flaw manifests when processing beacon frames in a specific sequence that violates expected wireless protocol behavior, creating a scenario where the kernel's wireless scanning logic fails catastrophically.
The technical root cause of this vulnerability lies in the cmp_ies function within the net/wireless/scan.c file, which handles the comparison of information elements in wireless beacon frames. When the wireless subsystem encounters a sequence where a beacon frame omits an SSID Information Element followed by a subsequent frame that includes an SSID IE, the function fails to properly handle the NULL pointer dereference that occurs during this comparison operation. This condition arises because the code does not adequately validate the presence of required information elements before attempting to process them, leading to an unhandled null pointer access that results in kernel panic and system crash.
The operational impact of this vulnerability extends beyond simple system instability, as it can severely disrupt wireless networking services in affected systems. Network administrators and users relying on wireless connectivity may experience unexpected system crashes, particularly in environments where wireless devices frequently scan and connect to multiple networks. The vulnerability is particularly concerning in enterprise and infrastructure environments where wireless access points and client devices are constantly exchanging beacon frames, as the denial of service can persist until the system is manually rebooted or the wireless subsystem is restarted.
This vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and demonstrates how improper input validation can lead to system crashes in kernel space. From an ATT&CK framework perspective, this represents a privilege escalation vector through system resource exhaustion and denial of service, potentially allowing attackers to disrupt wireless services and compromise network availability. The attack requires minimal privileges as it operates at the network level, making it particularly dangerous in environments where wireless access is critical for operations. The fix implemented in kernel version 2.6.31-rc6 involved proper validation of information element presence and robust handling of NULL pointers during beacon frame processing, ensuring that the wireless subsystem can gracefully handle malformed or unexpected wireless frames without crashing the entire system.