CVE-2011-4080 in Linux
Summary
by MITRE
The sysrq_sysctl_handler function in kernel/sysctl.c in the Linux kernel before 2.6.39 does not require the CAP_SYS_ADMIN capability to modify the dmesg_restrict value, which allows local users to bypass intended access restrictions and read the kernel ring buffer by leveraging root privileges, as demonstrated by a root user in a Linux Containers (aka LXC) environment.
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Analysis
by VulDB Data Team • 03/04/2025
The vulnerability identified as CVE-2011-4080 represents a critical privilege escalation flaw within the Linux kernel's sysctl subsystem that undermines fundamental security controls designed to protect kernel ring buffer access. This issue affects Linux kernel versions prior to 2.6.39 and specifically targets the sysrq_sysctl_handler function located in kernel/sysctl.c. The flaw stems from inadequate capability checks that should have enforced the CAP_SYS_ADMIN permission level before allowing modifications to the dmesg_restrict parameter, which controls access to kernel messages stored in the ring buffer.
The technical implementation of this vulnerability exploits the absence of proper capability validation within the sysctl handler mechanism. When the dmesg_restrict value is modified without requiring the appropriate CAP_SYS_ADMIN capability, local users can manipulate this setting to gain unauthorized access to kernel ring buffer contents. This represents a direct violation of the principle of least privilege and undermines the security model that separates user-space processes from privileged kernel operations. The vulnerability becomes particularly dangerous in containerized environments such as Linux Containers (LXC) where privilege boundaries may be less strict, allowing a root user within a container to potentially escalate privileges and access sensitive kernel information.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass potential privilege escalation and system compromise. Attackers can leverage this flaw to read kernel ring buffer contents that often contain sensitive information including memory addresses, kernel module load information, and potentially confidential data from kernel memory regions. This access can facilitate further exploitation attempts by providing attackers with detailed insights into kernel internals and potential attack vectors. The vulnerability is particularly concerning in environments where containerization is prevalent, as it demonstrates how local privilege escalation within a container can be used to bypass isolation mechanisms and access kernel-level information that should remain protected.
The security implications align with CWE-284, which addresses improper access control in software systems, and represents a clear violation of the principle that privileged operations should require appropriate capabilities. From an ATT&CK perspective, this vulnerability maps to privilege escalation techniques and can be categorized under T1068, which involves exploiting weaknesses in the system to gain elevated privileges. The vulnerability also intersects with T1005, which involves data from local system information discovery, as attackers can gather sensitive kernel information through this mechanism. The flaw demonstrates how seemingly minor implementation oversights in kernel subsystems can create significant security risks that affect the entire system security posture.
Mitigation strategies for CVE-2011-4080 require immediate kernel version updates to 2.6.39 or later where the proper capability checks have been implemented. System administrators should also implement additional monitoring to detect unauthorized modifications to the dmesg_restrict parameter and consider disabling unnecessary sysctl interfaces when not required. The vulnerability underscores the importance of capability-based access controls in kernel space and highlights the necessity of comprehensive security reviews of privileged system interfaces. Organizations using containerized environments should particularly focus on ensuring their kernel versions are patched and implement proper security controls to prevent unauthorized access to kernel ring buffer contents that could be exploited to compromise system integrity.