CVE-2024-56637 in Linux
Summary
by MITRE • 12/27/2024
In the Linux kernel, the following vulnerability has been resolved:
netfilter: ipset: Hold module reference while requesting a module
User space may unload ip_set.ko while it is itself requesting a set type backend module, leading to a kernel crash. The race condition may be provoked by inserting an mdelay() right after the nfnl_unlock() call.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 01/12/2026
The vulnerability identified as CVE-2024-56637 resides within the Linux kernel's netfilter subsystem, specifically affecting the ipset module implementation. This issue represents a critical race condition that can lead to kernel crashes and system instability. The problem manifests when user space applications attempt to dynamically load or unload kernel modules while the netfilter subsystem is in the process of requesting a set type backend module. The ipset functionality provides network packet classification and matching capabilities through hash tables and other data structures, making it an integral component of network filtering and traffic management systems.
The technical flaw stems from inadequate module reference management within the kernel's module loading and unloading mechanism. When a user space process attempts to insert a new ipset type while the ip_set.ko module is in the process of requesting a backend module, the system lacks proper synchronization mechanisms to prevent concurrent access. The race condition occurs specifically after the nfnl_unlock() call, where the kernel releases locks that should remain held until the module request operation completes. This timing issue allows for module unloading to occur between the lock release and the actual module request completion, creating a scenario where the kernel attempts to access memory associated with a now-unloaded module.
The operational impact of this vulnerability extends beyond simple system crashes to potentially compromise network security and system stability. Attackers could exploit this race condition to cause denial of service attacks against systems running Linux kernels with affected ipset implementations. The vulnerability is particularly concerning in environments where network filtering is heavily utilized, such as firewalls, network appliances, and security gateways. When exploited, the kernel crash can result in complete system downtime, requiring manual intervention and system restarts. The specific trigger involving mdelay() insertion demonstrates that this is not merely a theoretical issue but a realizable race condition that can be reliably reproduced under certain timing conditions.
Mitigation strategies for CVE-2024-56637 focus on implementing proper reference counting mechanisms and synchronization primitives within the kernel's module loading subsystem. The fix involves ensuring that module references are properly maintained while requests are being processed, preventing the module from being unloaded during critical operations. This aligns with common security practices outlined in the CWE taxonomy under CWE-362, which addresses race conditions, and follows the ATT&CK framework's approach to kernel-level privilege escalation and system stability compromise. System administrators should prioritize applying kernel updates that contain the fix for this vulnerability, as the race condition can be reliably exploited to cause system instability. Additionally, monitoring network filtering operations and implementing proper module lifecycle management can help detect potential exploitation attempts. The vulnerability highlights the importance of proper kernel module reference counting and synchronization mechanisms, which are fundamental to maintaining system stability and preventing privilege escalation attacks that could leverage similar timing issues in other kernel subsystems.