CVE-2011-3209 in Linux
Summary
by MITRE
The div_long_long_rem implementation in include/asm-x86/div64.h in the Linux kernel before 2.6.26 on the x86 platform allows local users to cause a denial of service (Divide Error Fault and panic) via a clock_gettime system call.
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Analysis
by VulDB Data Team • 12/14/2021
The vulnerability identified as CVE-2011-3209 represents a critical flaw in the Linux kernel's handling of division operations on x86 platforms. This issue specifically affects the div_long_long_rem function located in the include/asm-x86/div64.h file, which is part of the kernel's arithmetic division implementation. The vulnerability arises from insufficient input validation and error handling within the division routine that processes 64-bit division operations on 32-bit systems. When a local user executes a clock_gettime system call, the kernel's division handler encounters a scenario that triggers an unhandled exception condition, leading to a system-wide crash. The flaw is classified under CWE-129 as an improper validation of array indices, specifically manifesting as an invalid division operation that results in a divide error fault. This vulnerability operates at the kernel level and demonstrates the critical nature of arithmetic operations in system stability.
The technical exploitation of this vulnerability occurs through the manipulation of system calls that ultimately invoke the problematic division routine. The clock_gettime system call, when processed through the x86 kernel division implementation, creates conditions where the divisor becomes zero or otherwise invalidates the division operation. The div_long_long_rem function fails to properly handle these edge cases, causing the processor to generate a divide error exception that is not gracefully handled by the kernel's exception handling mechanisms. This results in an immediate system panic and complete denial of service for the affected system. The vulnerability is particularly concerning because it can be triggered by any local user with access to the system, requiring no special privileges or network access. The attack vector operates through the standard system call interface, making it difficult to detect and prevent through traditional network-based security measures.
The operational impact of CVE-2011-3209 extends beyond simple system downtime, as it represents a fundamental weakness in the kernel's arithmetic processing capabilities. When exploited, this vulnerability can cause complete system crashes that require manual intervention for recovery, potentially leading to data loss or service disruption in critical environments. The vulnerability affects all Linux systems running kernel versions prior to 2.6.26 on x86 platforms, making it widespread and potentially exploitable across numerous production environments. Organizations relying on these kernel versions face significant risk, as the denial of service can be triggered repeatedly and may be used to maintain persistent system unavailability. The impact is particularly severe in server environments where continuous uptime is critical, and the vulnerability can be leveraged by attackers to create sustained service disruption or as part of more complex attack chains.
Mitigation strategies for CVE-2011-3209 focus primarily on upgrading to patched kernel versions where the division handling has been corrected. System administrators should immediately apply kernel updates to versions 2.6.26 or later, which contain the necessary fixes for the div_long_long_rem function. The patch addresses the root cause by implementing proper error checking and exception handling within the division routine, preventing the divide error condition from propagating to the system's exception handlers. Additional defensive measures include monitoring for unusual system call patterns that might indicate exploitation attempts, though this approach is less reliable given the local nature of the vulnerability. Organizations should also consider implementing kernel hardening techniques such as stack canaries and address space layout randomization to reduce the overall attack surface. From an ATT&CK perspective, this vulnerability aligns with techniques involving privilege escalation and denial of service, specifically mapping to T1499.004 for network denial of service and T1068 for local privilege escalation through kernel exploitation. The vulnerability underscores the importance of maintaining up-to-date system software and proper security patch management protocols to prevent exploitation of known kernel vulnerabilities.