CVE-2009-1243 in Linux
Summary
by MITRE
net/ipv4/udp.c in the Linux kernel before 2.6.29.1 performs an unlocking step in certain incorrect circumstances, which allows local users to cause a denial of service (panic) by reading zero bytes from the /proc/net/udp file and unspecified other files, related to the "udp seq_file infrastructure."
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Analysis
by VulDB Data Team • 04/14/2019
The vulnerability described in CVE-2009-1243 resides within the Linux kernel's network stack implementation, specifically in the udp.c file that handles User Datagram Protocol operations. This issue affects Linux kernel versions prior to 2.6.29.1 and represents a critical flaw in the kernel's handling of sequence file infrastructure used for network protocol information. The vulnerability manifests when the kernel processes certain read operations on network-related proc files, particularly the /proc/net/udp interface that provides information about UDP socket connections. The flaw occurs during the unlocking phase of kernel operations where improper state management leads to a kernel panic condition.
The technical implementation of this vulnerability exploits a race condition or improper locking mechanism within the UDP sequence file handling code. When local users attempt to read zero bytes from the /proc/net/udp file or other related network files, the kernel's internal locking mechanism fails to properly manage the resource state. This incorrect unlocking step causes the kernel to enter an inconsistent state where subsequent operations trigger a kernel panic, effectively crashing the system. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, though the specific manifestation involves improper locking rather than traditional buffer issues. The flaw leverages the kernel's seq_file infrastructure which is designed to provide a consistent interface for reading kernel data structures through proc filesystem entries.
From an operational perspective, this vulnerability presents a significant denial of service risk that can be exploited by any local user with access to the system. The impact extends beyond simple service disruption as the kernel panic can result in complete system crashes requiring manual reboot or automatic restart. The exploit requires minimal privileges and can be executed repeatedly, making it particularly dangerous in environments where local access is not properly restricted. The vulnerability affects systems running kernel versions before 2.6.29.1 and can be found in various distributions including older versions of Ubuntu, Debian, and Red Hat Enterprise Linux. This type of vulnerability aligns with ATT&CK technique T1499.004 for network denial of service, though the specific implementation involves kernel-level resource management rather than network layer attacks.
The mitigation strategy for CVE-2009-1243 involves upgrading to Linux kernel version 2.6.29.1 or later where the improper unlocking logic has been corrected. System administrators should implement immediate patching of affected systems and verify that all network-related proc files are properly secured through access controls. The vulnerability demonstrates the importance of proper locking mechanisms in kernel space operations and highlights the need for comprehensive testing of sequence file infrastructure. Organizations should also consider implementing monitoring for suspicious read operations on network proc files and establish proper access controls to limit local user privileges. The fix addresses the core issue by ensuring proper resource management during read operations and preventing the kernel from entering an inconsistent state that leads to panic conditions. This vulnerability serves as a reminder of the critical importance of kernel-level security testing and the potential for seemingly minor implementation flaws to result in severe system stability issues.