CVE-2009-2691 in Linux
Summary
by MITRE
The mm_for_maps function in fs/proc/base.c in the Linux kernel 2.6.30.4 and earlier allows local users to read (1) maps and (2) smaps files under proc/ via vectors related to ELF loading, a setuid process, and a race condition.
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability described in CVE-2009-2691 represents a critical privilege escalation flaw within the Linux kernel's process management subsystem. This issue affects kernel versions up to and including 2.6.30.4, where the mm_for_maps function in fs/proc/base.c fails to properly validate access permissions when processing memory mapping information for processes. The vulnerability specifically exploits a race condition that occurs during the ELF loading process, creating a window where local attackers can bypass normal access controls to read sensitive memory mapping data from other processes.
The technical implementation of this vulnerability stems from improper synchronization mechanisms within the kernel's memory management code. When a setuid process is loaded and subsequently accessed through the proc filesystem, particularly via the maps and smaps interface, the mm_for_maps function does not adequately enforce permission checks. This allows local users to construct malicious vectors that exploit the timing gap between when a process is loaded and when its memory mappings are properly secured. The race condition manifests during the ELF loading sequence, where the kernel's memory management structures are temporarily in an inconsistent state, enabling unauthorized access to memory mapping information that should be restricted.
The operational impact of this vulnerability is significant for system security, as it provides local attackers with access to memory mapping data that could reveal sensitive information about running processes. The maps file contains information about memory segments, including their addresses, permissions, and associated files, while smaps provides detailed statistics about memory usage. This information could be exploited to perform advanced attacks such as heap spraying, memory layout discovery, or to identify potential targets for further exploitation. The vulnerability particularly affects systems where setuid binaries are present, as these processes often have elevated privileges and their memory mappings contain sensitive data that could be leveraged for privilege escalation or information disclosure attacks.
This vulnerability aligns with CWE-284, which addresses improper access control in software systems, and relates to the broader category of privilege escalation flaws that attackers frequently target in kernel-level exploits. The ATT&CK framework would classify this under T1068, which covers 'Exploitation for Privilege Escalation,' and potentially T1059, 'Command and Scripting Interpreter,' as attackers might use the leaked memory information to craft more sophisticated attack vectors. The race condition aspect of this vulnerability also connects to ATT&CK technique T1499, 'Endpoint Denial of Service,' as the improper handling of memory mappings could potentially lead to system instability. Organizations should implement immediate mitigations including kernel updates to versions 2.6.30.5 and later, where the race condition has been addressed through proper synchronization mechanisms and enhanced access control validation in the mm_for_maps function. Additionally, monitoring for unauthorized access to /proc//maps and /proc//smaps files should be implemented to detect potential exploitation attempts.