CVE-2009-2909 in Linux
Summary
by MITRE
Integer signedness error in the ax25_setsockopt function in net/ax25/af_ax25.c in the ax25 subsystem in the Linux kernel before 2.6.31.2 allows local users to cause a denial of service (OOPS) via a crafted optlen value in an SO_BINDTODEVICE operation.
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Analysis
by VulDB Data Team • 08/24/2021
The vulnerability identified as CVE-2009-2909 represents a critical integer signedness error within the Linux kernel's ax25 subsystem, specifically affecting the ax25_setsockopt function located in net/ax25/af_ax25.c. This flaw exists in kernel versions prior to 2.6.31.2 and demonstrates a fundamental issue in how the system handles socket option length parameters during network device binding operations. The ax25 protocol is part of the Amateur Radio AX.25 packet layer protocol suite used primarily in amateur radio communications over packet radio networks, making this vulnerability particularly concerning for systems relying on such communication infrastructures.
The technical root cause of this vulnerability stems from an improper handling of signed and unsigned integer types within the socket option processing logic. When a local user executes a SO_BINDTODEVICE operation with a crafted optlen value, the system fails to properly validate the signedness of the integer parameter, leading to unpredictable behavior in memory management operations. This signedness error occurs because the kernel code does not correctly account for the difference between signed and unsigned integer representations when processing the socket option length parameter. The flaw specifically manifests during the ax25_setsockopt function execution, where an improperly validated optlen value causes the kernel to attempt memory operations with invalid parameters, ultimately resulting in a kernel oops condition.
The operational impact of this vulnerability is significant as it enables a local attacker to trigger a denial of service condition that causes the kernel to crash or become unresponsive. An attacker with local access can exploit this vulnerability by constructing a malicious socket option with an specifically crafted optlen value that exploits the integer signedness error. When the kernel processes this malformed parameter, it results in an invalid memory access pattern that generates a kernel oops, effectively crashing the system or rendering it unresponsive to further network operations. This type of denial of service can have severe implications for systems relying on amateur radio communications or other applications using the ax25 protocol, potentially disrupting critical communication links.
This vulnerability maps to CWE-192, which specifically addresses "Integer Underflow or Overflow in a Signed Integer" and falls under the broader category of integer handling errors in kernel space operations. The attack pattern aligns with ATT&CK technique T1499.004, which covers "Endpoint Denial of Service" through kernel-level exploits. The vulnerability demonstrates the importance of proper input validation in kernel space operations, particularly when dealing with socket option parameters and memory management. The exploitation requires local access but can result in system-wide disruption, making it a particularly dangerous flaw in networked systems where local users might have access to kernel interfaces.
Mitigation strategies for this vulnerability include upgrading to Linux kernel version 2.6.31.2 or later, where the integer signedness error has been corrected through proper parameter validation and type handling. System administrators should also implement proper access controls to limit local user privileges and monitor for unusual socket operations that might indicate exploitation attempts. The fix implemented in the patched kernel version addresses the specific integer handling issue by ensuring proper signedness validation before processing socket option length parameters, preventing the kernel from attempting invalid memory operations that would lead to the oops condition. Organizations using systems with amateur radio communication capabilities should prioritize this update to maintain system stability and prevent potential disruption of critical communication infrastructure.