CVE-2011-2495 in Linux
Summary
by MITRE
fs/proc/base.c in the Linux kernel before 2.6.39.4 does not properly restrict access to /proc/#####/io files, which allows local users to obtain sensitive I/O statistics by polling a file, as demonstrated by discovering the length of another user s password.
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Analysis
by VulDB Data Team • 12/03/2021
The vulnerability identified as CVE-2011-2495 resides within the Linux kernel's proc filesystem implementation, specifically in the fs/proc/base.c file. This flaw represents a privilege escalation issue that affects Linux kernel versions prior to 2.6.39.4, creating a significant security gap in the operating system's access control mechanisms. The vulnerability stems from inadequate permission checking when accessing /proc/#####/io files, where ##### represents process identifiers, allowing unauthorized access to I/O statistics data that should be restricted to the owning user or processes with appropriate privileges.
The technical flaw manifests in the improper restriction of access controls for I/O statistics files within the proc filesystem. When a local user attempts to access another user's /proc/#####/io file, the kernel fails to properly validate the requesting process's privileges, enabling information disclosure through polling mechanisms. This weakness allows attackers to gather sensitive data about other processes by monitoring I/O operations, particularly enabling them to determine the length of passwords or other sensitive information without direct access to the underlying process data. The vulnerability operates at the kernel level and demonstrates a critical failure in the kernel's security model for managing process-specific information.
The operational impact of this vulnerability extends beyond simple information disclosure, as it provides attackers with a method to perform passive reconnaissance and potentially facilitate more sophisticated attacks. By polling I/O statistics files, attackers can infer password lengths and other sensitive information through timing analysis and statistical correlation. This capability undermines the fundamental security principle of process isolation and can be leveraged in combination with other techniques to compromise user accounts or system integrity. The vulnerability particularly affects systems where multiple users share the same machine, as it enables one user to gather information about processes belonging to other users.
This vulnerability aligns with CWE-200, which addresses "Information Exposure," and demonstrates how insufficient access control mechanisms can lead to unauthorized information disclosure. From an ATT&CK perspective, this issue relates to T1083 (File and Directory Discovery) and T1552 (Unsecured Credentials), as it enables adversaries to discover and extract sensitive information from the system. The vulnerability also connects to T1059 (Command and Scripting Interpreter) through potential exploitation methods that might involve shell commands to access the proc filesystem. Organizations should implement kernel updates to address this vulnerability, as the patch in kernel version 2.6.39.4 properly restricts access to /proc/#####/io files and enforces appropriate access controls. Additionally, system administrators should conduct regular security audits to ensure that all systems are running patched kernel versions and that unnecessary processes are not running with elevated privileges that could exacerbate the impact of such vulnerabilities.