CVE-2011-2521 in Linux
Summary
by MITRE
The x86_assign_hw_event function in arch/x86/kernel/cpu/perf_event.c in the Performance Events subsystem in the Linux kernel before 2.6.39 does not properly calculate counter values, which allows local users to cause a denial of service (panic) via the perf program.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability identified as CVE-2011-2521 resides within the Linux kernel's Performance Events subsystem, specifically in the x86_assign_hw_event function located in arch/x86/kernel/cpu/perf_event.c. This flaw represents a critical design oversight that affects kernel versions prior to 2.6.39, creating a potential pathway for local attackers to execute denial of service attacks through carefully crafted perf program executions. The issue manifests when the kernel fails to properly calculate counter values during hardware performance event assignment, leading to system instability and potential system crashes.
The technical root cause of this vulnerability stems from improper handling of counter calculations within the performance monitoring framework. When the x86_assign_hw_event function processes hardware event assignments, it fails to validate or properly compute the counter values required for performance monitoring operations. This miscalculation can result in invalid memory access patterns or arithmetic overflow conditions that trigger kernel panic states. The flaw operates at the kernel level, making it particularly dangerous as it bypasses typical user-space protections and operates with the highest privilege levels. According to CWE classification, this vulnerability maps to CWE-129: Improper Validation of Array Indices, as the improper counter calculation effectively creates invalid array access patterns within the kernel's performance monitoring structures.
The operational impact of CVE-2011-2521 extends beyond simple system disruption, as local users with basic privileges can exploit this weakness to cause complete system crashes. The perf program, which is commonly used for performance analysis and monitoring, becomes a vector for malicious activity when executed with crafted parameters that trigger the flawed counter calculation logic. This vulnerability represents a classic example of how kernel-level flaws can be leveraged for denial of service attacks without requiring elevated privileges or sophisticated exploitation techniques. The attack surface is particularly concerning as it affects systems running kernel versions before 2.6.39, which were widely deployed across enterprise and consumer environments during that time period.
Mitigation strategies for CVE-2011-2521 primarily focus on kernel version upgrades to 2.6.39 or later, where the counter calculation logic has been corrected. System administrators should prioritize patching affected systems, particularly those running older kernel versions that remain in production environments. Additionally, monitoring for unauthorized perf program execution and implementing privilege controls can help reduce the attack surface. From an ATT&CK framework perspective, this vulnerability aligns with T1499.004: Endpoint Denial of Service, as it enables local users to consume system resources or trigger conditions that lead to system unavailability. Organizations should also consider implementing kernel hardening measures such as kernel address space layout randomization and disabling unnecessary performance monitoring features on systems where they are not required. The vulnerability serves as a reminder of the critical importance of thorough testing and validation of kernel subsystems, particularly those handling hardware-level operations and performance monitoring functions.