CVE-2011-1022 in libcgroup
Summary
by MITRE
The cgre_receive_netlink_msg function in daemon/cgrulesengd.c in cgrulesengd in the Control Group Configuration Library (aka libcgroup or libcg) before 0.37.1 does not verify that netlink messages originated in the kernel, which allows local users to bypass intended resource restrictions via a crafted message.
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Analysis
by VulDB Data Team • 10/21/2021
The vulnerability identified as CVE-2011-1022 resides within the Control Group Configuration Library commonly known as libcgroup or libcg which serves as a critical component for managing Linux control groups and their associated resource controls. This library provides the infrastructure necessary for organizing processes into hierarchical groups and enforcing resource limits such as CPU usage, memory allocation, and disk I/O. The specific flaw exists in the cgre_receive_netlink_msg function located in daemon/cgrulesengd.c, which handles netlink message processing for control group rules enforcement. The function fails to validate the source of incoming netlink messages, creating a fundamental security gap that undermines the entire resource restriction mechanism.
The technical flaw stems from the absence of proper message origin verification within the netlink communication channel. Netlink sockets provide a bidirectional communication mechanism between user-space processes and the kernel, commonly used for system administration tasks. In this case, the cgre_receive_netlink_msg function accepts messages without confirming whether they originated from the kernel itself, rather than from potentially malicious local users. This omission creates a privilege escalation vector where a local attacker can craft and inject specially formatted netlink messages that appear to come from the kernel. When processed by the vulnerable function, these forged messages can manipulate control group configurations and bypass established resource limits, effectively allowing unauthorized access to system resources that should be restricted.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally compromises the security model of control group implementations. Control groups are designed to isolate processes and limit their resource consumption to prevent system-wide resource exhaustion and ensure fair resource allocation among competing processes. When local users can bypass these restrictions, they gain the ability to consume excessive system resources, potentially causing denial of service conditions or resource starvation for other legitimate processes. This vulnerability particularly affects systems that rely heavily on control group enforcement for security isolation, such as containerized environments, virtualization platforms, and multi-tenant systems where resource boundaries must be strictly maintained. The flaw enables attackers to manipulate resource limits in ways that could lead to system instability, performance degradation, or even complete system compromise.
Mitigation strategies for this vulnerability require immediate patching of the libcgroup library to version 0.37.1 or later, which includes proper message origin verification. The fix should implement kernel source validation for netlink messages, ensuring that only messages originating from the kernel can influence control group configurations. Organizations should also consider implementing additional monitoring and logging of control group operations to detect anomalous behavior that might indicate exploitation attempts. From a defensive perspective, this vulnerability aligns with CWE-20, "Improper Input Validation," and represents a classic case of insufficient validation of source authenticity in kernel communication channels. The ATT&CK framework would classify this under T1068, "Exploitation for Privilege Escalation," and potentially T1496, "Resource Hijacking," as it enables unauthorized resource consumption. System administrators should also review and audit existing control group configurations to ensure proper access controls and monitor for unusual resource usage patterns that might indicate exploitation of this vulnerability.