CVE-2012-2127 in Linux
Summary
by MITRE
fs/proc/root.c in the procfs implementation in the Linux kernel before 3.2 does not properly interact with CLONE_NEWPID clone system calls, which allows remote attackers to cause a denial of service (reference leak and memory consumption) by making many connections to a daemon that uses PID namespaces to isolate clients, as demonstrated by vsftpd.
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Analysis
by VulDB Data Team • 12/05/2021
The vulnerability described in CVE-2012-2127 represents a critical flaw in the Linux kernel's procfs implementation that emerged from improper handling of PID namespace isolation mechanisms. This issue specifically affects Linux kernel versions prior to 3.2 and stems from the kernel's failure to correctly manage reference counting when processing clone system calls with the CLONE_NEWPID flag. The procfs subsystem, which provides an interface for accessing kernel data structures through a virtual filesystem, becomes vulnerable when PID namespaces are employed to isolate processes, creating a scenario where resource management breaks down under specific conditions.
The technical root cause of this vulnerability lies in the interaction between the procfs implementation and the PID namespace functionality within the kernel. When applications utilize the CLONE_NEWPID flag to create new PID namespaces, the kernel's procfs layer fails to properly decrement reference counts for certain kernel objects. This reference leak occurs because the kernel does not adequately account for the relationship between process identifiers and their corresponding filesystem entries when namespaces are created and destroyed. The flaw manifests particularly when daemons that employ PID namespace isolation make extensive use of the clone system call, as demonstrated in the vsftpd exploit scenario.
The operational impact of this vulnerability is significant, as it enables remote attackers to perform denial of service attacks through memory exhaustion. By establishing numerous connections to a vulnerable daemon that employs PID namespace isolation, an attacker can trigger the reference leak condition repeatedly. Each connection creates a new process within a separate PID namespace, leading to accumulation of unreleased kernel memory objects. Over time, this results in progressive memory consumption that can eventually cause system instability or complete system crashes. The vulnerability is particularly dangerous because it can be exploited remotely without requiring authentication, making it a serious threat to network services that rely on PID namespace isolation for security separation.
The exploitability of CVE-2012-2127 demonstrates the importance of proper resource management in kernel space operations and aligns with CWE-404, which addresses improper resource release or cleanup. This vulnerability also relates to ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. The issue highlights the challenges of maintaining correct reference counting in complex kernel subsystems where multiple isolation mechanisms interact. Organizations using affected kernel versions face the risk of service disruption, particularly in environments where daemons rely heavily on namespace isolation for security purposes. The vulnerability underscores the critical need for thorough testing of kernel components when implementing new isolation features, as well as the importance of timely security updates to address such fundamental resource management flaws.
Mitigation strategies for this vulnerability primarily involve upgrading to Linux kernel version 3.2 or later, where the reference counting issue has been resolved through proper implementation of the procfs interaction with PID namespace operations. System administrators should also consider implementing monitoring for unusual memory consumption patterns and establishing automated alerting for processes that may be triggering the reference leak condition. Additionally, organizations can reduce the attack surface by limiting the use of PID namespace isolation in applications where it is not strictly necessary, though this approach may compromise security benefits in environments where such isolation is critical for protecting against process-level attacks. The fix implemented in kernel 3.2 addresses the fundamental reference counting issue and ensures proper cleanup of kernel resources when PID namespaces are created and destroyed, thereby preventing the memory consumption escalation that enabled the denial of service attack.