CVE-2012-2123 in Linux
Summary
by MITRE
The cap_bprm_set_creds function in security/commoncap.c in the Linux kernel before 3.3.3 does not properly handle the use of file system capabilities (aka fcaps) for implementing a privileged executable file, which allows local users to bypass intended personality restrictions via a crafted application, as demonstrated by an attack that uses a parent process to disable ASLR.
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Analysis
by VulDB Data Team • 03/24/2021
The vulnerability described in CVE-2012-2123 represents a critical flaw in the Linux kernel's capability handling mechanism that specifically affects versions prior to 3.3.3. This issue resides within the cap_bprm_set_creds function located in security/commoncap.c, which is responsible for managing credential settings during program execution. The flaw fundamentally undermines the kernel's ability to properly enforce file system capabilities, commonly referred to as fcaps, which are designed to provide fine-grained privilege control for executable files without requiring full root privileges. The vulnerability manifests when the kernel fails to correctly process these extended capabilities during the execution of privileged programs, creating an exploitable condition that can be leveraged by local attackers to circumvent security restrictions.
The technical implementation of this vulnerability stems from the improper handling of file system capabilities within the kernel's binary execution framework. When a program with file system capabilities attempts to execute, the cap_bprm_set_creds function should properly validate and enforce the capability restrictions associated with that program. However, due to the flaw in the implementation, the kernel fails to correctly interpret the capability settings, allowing malicious applications to manipulate the execution environment. This misconfiguration particularly affects the handling of personality restrictions, which are system-level security features designed to prevent certain types of exploitation by controlling aspects of the process execution environment. The vulnerability enables attackers to craft applications that can disable critical security features such as Address Space Layout Randomization, which is essential for preventing various exploitation techniques including return-oriented programming attacks and stack buffer overflows.
The operational impact of CVE-2012-2123 extends beyond simple privilege escalation to encompass broader system compromise capabilities. Attackers can leverage this vulnerability to bypass ASLR, a fundamental security mitigation that randomizes memory layout to make exploitation more difficult. By disabling ASLR through the crafted application, attackers gain significant advantages in performing memory corruption attacks and other exploitation techniques that rely on predictable memory addresses. The vulnerability also affects the broader capability-based security model of Linux, potentially allowing attackers to escalate privileges beyond what would normally be permitted by the system's capability framework. This creates a cascading effect where the compromise of a single vulnerable application can provide attackers with elevated privileges and access to system resources that should otherwise be restricted. The flaw particularly impacts systems running older kernel versions where the capability handling mechanisms have not been updated to properly address the file system capability processing.
Mitigation strategies for this vulnerability primarily focus on kernel version updates and system hardening measures. The most effective solution involves upgrading to Linux kernel version 3.3.3 or later, where the cap_bprm_set_creds function has been properly patched to correctly handle file system capabilities. System administrators should also implement additional security measures including regular kernel updates, capability-based access controls, and monitoring for unauthorized privilege escalation attempts. The vulnerability aligns with CWE-264, which addresses permissions, privileges, and access controls, and demonstrates the importance of proper capability handling in kernel security. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and can be used to establish persistent access to systems, particularly when combined with other exploitation methods that target memory corruption vulnerabilities or process manipulation capabilities. Organizations should also consider implementing process monitoring and capability auditing to detect potential exploitation attempts and maintain visibility into privilege changes within their systems.