CVE-2011-0726 in Linux
Summary
by MITRE
The do_task_stat function in fs/proc/array.c in the Linux kernel before 2.6.39-rc1 does not perform an expected uid check, which makes it easier for local users to defeat the ASLR protection mechanism by reading the start_code and end_code fields in the /proc/#####/stat file for a process executing a PIE binary.
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Analysis
by VulDB Data Team • 11/14/2021
The vulnerability described in CVE-2011-0726 represents a significant security flaw in the Linux kernel's process information handling mechanism that directly impacts address space layout randomization protections. This weakness exists within the do_task_stat function located in the fs/proc/array.c file of the kernel source code, specifically affecting versions prior to 2.6.39-rc1. The flaw stems from an insufficient validation of user permissions when processing requests for process statistics through the /proc filesystem interface, creating an avenue for local privilege escalation and bypass of security mitigations.
The technical implementation of this vulnerability exploits a missing uid check within the kernel's process statistics reporting functionality. When a local user accesses the /proc/#####/stat file for a process executing a Position Independent Executable (PIE) binary, the system fails to verify that the requesting user has appropriate permissions to access this sensitive information. This omission allows unauthorized users to extract the start_code and end_code memory address values from the process's stat file, which are critical components in determining the memory layout of the running process. The absence of proper access controls in this kernel function creates a direct pathway for information disclosure that undermines the effectiveness of ASLR mechanisms.
The operational impact of this vulnerability extends beyond simple information disclosure, as it specifically targets the fundamental security mitigation of Address Space Layout Randomization. By enabling local users to obtain memory layout information from PIE binaries, attackers can effectively defeat ASLR protections that are designed to randomize memory addresses and make exploitation of other vulnerabilities more difficult. This information disclosure allows adversaries to predict memory locations and potentially exploit other vulnerabilities in the same process or related memory regions. The vulnerability is particularly dangerous because it operates at the kernel level and requires no special privileges beyond local user access, making it an attractive target for attackers seeking to escalate privileges or bypass security protections.
The flaw aligns with CWE-284 Access Control Issues, specifically related to insufficient privileges or incorrect access control mechanisms in kernel space operations. From an ATT&CK framework perspective, this vulnerability maps to T1068 Local Privilege Escalation and T1082 System Information Discovery, as it enables attackers to gather system information that can be used to facilitate further exploitation. The vulnerability demonstrates how seemingly minor access control oversights in kernel code can have significant security implications, particularly when they affect core operating system protections like ASLR. This type of information disclosure vulnerability is particularly concerning because it operates silently in the background and can be leveraged as a stepping stone for more sophisticated attacks.
Mitigation strategies for CVE-2011-0726 primarily involve upgrading to Linux kernel versions 2.6.39-rc1 or later, where the missing uid check has been properly implemented. System administrators should also consider implementing additional monitoring for unusual access patterns to /proc filesystem entries and ensure that all systems are running patched kernel versions. Organizations should conduct regular security audits to identify other potential access control vulnerabilities in kernel modules and ensure that proper privilege validation is implemented throughout the system. The vulnerability highlights the importance of thorough security reviews of kernel code, particularly in areas dealing with process information and access controls, as even small oversights can have significant security implications for the entire system.