CVE-2004-0491 in Enterprise Linux
Summary
by MITRE
The linux-2.4.21-mlock.patch in Red Hat Enterprise Linux 3 does not properly maintain the mlock page count when one process unlocks pages that belong to another process, which allows local users to mlock more memory than specified by the rlimit.
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Analysis
by VulDB Data Team • 06/11/2019
The vulnerability described in CVE-2004-0491 represents a critical flaw in the Linux kernel's memory management subsystem specifically within the mlock functionality. This issue affects Red Hat Enterprise Linux 3 systems that utilize the linux-2.4.21-mlock.patch patch, which was designed to enhance memory locking capabilities but inadvertently introduced a significant security weakness. The flaw exists in the kernel's handling of memory locking operations and directly impacts how the system tracks locked memory pages across different processes.
The technical root cause of this vulnerability lies in the improper maintenance of the mlock page count mechanism within the kernel's memory management code. When processes perform memory locking operations using mlock or mlockall system calls, the kernel maintains a count of locked pages to enforce resource limits imposed by the rlimit settings. However, the flawed implementation in the mlock.patch fails to correctly update these counts when one process unlocks memory pages that actually belong to another process. This mismanagement creates a scenario where the kernel's accounting system becomes inconsistent and inaccurate.
The operational impact of this vulnerability is particularly severe for local attackers who can exploit this flaw to circumvent memory resource limits imposed by the system. Through careful manipulation of memory locking and unlocking operations across multiple processes, an attacker can effectively lock more memory than permitted by their rlimit settings. This behavior violates fundamental security principles of resource management and can lead to several detrimental outcomes including potential denial of service attacks against other processes, system instability, or resource exhaustion that affects system-wide performance. The vulnerability essentially allows privilege escalation within the context of the local user's capabilities, enabling them to consume system resources beyond normal constraints.
This vulnerability maps directly to CWE-121 in the Common Weakness Enumeration, which describes "Stack-based Buffer Overflow" but more accurately reflects the resource management weakness present in this case. The flaw also aligns with ATT&CK technique T1496, which covers "Resource Hijacking, specifically focusing on memory exhaustion attacks that can be facilitated by improper resource accounting. The patch in question was intended to provide enhanced memory locking capabilities but instead created a path for unauthorized memory consumption that undermines the security model of the operating system. System administrators and security professionals should recognize this as a critical issue requiring immediate attention, particularly in environments where multiple users share system resources and where memory management policies are enforced through rlimit configurations.
The mitigation strategy for this vulnerability involves applying the appropriate kernel patches provided by Red Hat to correct the mlock page count maintenance logic. Organizations should also consider implementing additional monitoring mechanisms to detect unusual memory locking patterns and establish more robust resource management policies. Regular system updates and security assessments are essential to prevent exploitation of such fundamental kernel-level flaws that can significantly impact system stability and security posture.