CVE-2009-2768 in Linux
Summary
by MITRE
The load_flat_shared_library function in fs/binfmt_flat.c in the flat subsystem in the Linux kernel before 2.6.31-rc6 allows local users to cause a denial of service (NULL pointer dereference and system crash) or possibly have unspecified other impact by executing a shared flat binary, which triggers an access of an "uninitialized cred pointer."
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Analysis
by VulDB Data Team • 08/20/2021
The vulnerability described in CVE-2009-2768 resides within the Linux kernel's flat binary format subsystem, specifically in the load_flat_shared_library function located in fs/binfmt_flat.c. This flaw represents a critical security issue affecting Linux kernel versions prior to 2.6.31-rc6, where the kernel's handling of flat binary executables contains a fundamental programming error that can be exploited by local attackers to compromise system stability and potentially achieve further malicious objectives. The flat binary format is a legacy executable format used primarily for embedded systems and older applications, making this vulnerability particularly concerning for systems that still rely on such compatibility layers.
The technical root cause of this vulnerability stems from an uninitialized credential pointer within the load_flat_shared_library function, which creates a NULL pointer dereference condition when processing shared flat binaries. When a local user executes a specially crafted flat binary, the kernel's execution path fails to properly initialize the credential structure pointer before attempting to access it, leading to immediate system crash and denial of service conditions. This uninitialized variable issue falls under the CWE-457 category of "Use of Uninitialized Variable" and represents a classic null pointer dereference vulnerability that can be exploited to crash kernel space processes. The flaw occurs during the binary loading process when the kernel attempts to establish proper access controls and security contexts for the executed flat binary.
The operational impact of this vulnerability extends beyond simple denial of service, as the potential for unspecified other impacts suggests that local attackers could leverage this weakness to achieve more sophisticated exploitation techniques. The system crash resulting from NULL pointer dereference can be reliably triggered by any local user with the ability to execute flat binaries, making this a particularly dangerous vulnerability in multi-user environments where privilege escalation or persistent system compromise might be possible. The flat binary format support in the Linux kernel is typically used for embedded applications, but the presence of this vulnerability means that any system running older kernel versions could be compromised, potentially allowing attackers to gain unauthorized access to system resources or disrupt critical services.
Mitigation strategies for CVE-2009-2768 primarily involve upgrading to Linux kernel versions 2.6.31-rc6 or later, where the vulnerability has been addressed through proper initialization of the credential pointer within the load_flat_shared_library function. System administrators should prioritize patching affected systems, particularly those running embedded or legacy applications that rely on flat binary format support. Additional protective measures include disabling unnecessary binary format handlers through kernel configuration options, implementing strict file access controls to limit execution permissions for flat binaries, and monitoring system logs for suspicious execution patterns. The vulnerability demonstrates the importance of proper variable initialization in kernel space code and aligns with ATT&CK technique T1068 which covers "Exploitation for Privilege Escalation" through kernel vulnerabilities, emphasizing that such flaws can be exploited to gain elevated system privileges. Organizations should also consider implementing kernel hardening techniques and regularly auditing their kernel configurations to prevent similar issues from arising in other subsystems.