CVE-2024-39503 in Linux
Summary
by MITRE • 07/12/2024
In the Linux kernel, the following vulnerability has been resolved:
netfilter: ipset: Fix race between namespace cleanup and gc in the list:set type
Lion Ackermann reported that there is a race condition between namespace cleanup in ipset and the garbage collection of the list:set type. The namespace cleanup can destroy the list:set type of sets while the gc of the set type is waiting to run in rcu cleanup. The latter uses data from the destroyed set which thus leads use after free. The patch contains the following parts:
- When destroying all sets, first remove the garbage collectors, then wait if needed and then destroy the sets. - Fix the badly ordered "wait then remove gc" for the destroy a single set case. - Fix the missing rcu locking in the list:set type in the userspace test case. - Use proper RCU list handlings in the list:set type.
The patch depends on c1193d9bbbd3 (netfilter: ipset: Add list flush to cancel_gc).
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Analysis
by VulDB Data Team • 09/17/2025
The vulnerability CVE-2024-39503 represents a critical race condition within the Linux kernel's netfilter subsystem, specifically affecting the ipset module's handling of namespace cleanup operations and garbage collection processes. This issue manifests in the list:set type implementation where concurrent operations between namespace cleanup routines and garbage collection mechanisms create a scenario that can lead to use-after-free conditions. The vulnerability was identified through careful analysis of concurrent execution paths within the kernel's networking subsystem, where the destruction of ipset data structures occurs simultaneously with garbage collection processes that depend on those same structures.
The technical flaw stems from improper ordering of operations during ipset destruction, particularly when dealing with namespace cleanup and garbage collection components. When the kernel attempts to destroy all sets within a namespace, it fails to properly sequence the removal of garbage collectors before proceeding with set destruction. This creates a window where garbage collection processes can attempt to access memory regions that have already been freed, resulting in memory corruption and potential privilege escalation. The race condition specifically affects the list:set type implementation, which maintains complex data structures that require careful synchronization between different kernel subsystems.
The operational impact of this vulnerability extends beyond simple memory corruption to potentially enable privilege escalation and system instability. An attacker who can trigger the specific race condition may be able to execute arbitrary code with kernel privileges, effectively bypassing kernel security mechanisms. The vulnerability affects systems running Linux kernel versions that include the affected ipset module functionality, particularly those implementing network filtering and packet classification policies. This creates a significant risk for network infrastructure devices, firewalls, and systems that rely heavily on netfilter-based packet filtering and access control mechanisms.
Mitigation strategies for CVE-2024-39503 require immediate kernel updates to apply the patched code that reorders the destruction sequence and implements proper RCU (Read-Copy-Update) locking mechanisms. The fix addresses the core issue by ensuring that garbage collectors are removed and waited upon before proceeding with set destruction, thereby eliminating the race condition window. Additionally, system administrators should monitor for any kernel updates that include this patch and verify that all network filtering configurations are properly tested after applying the update. The solution aligns with CWE-362 standards for concurrent execution issues and addresses ATT&CK techniques related to privilege escalation through kernel vulnerabilities. Organizations should also implement proper kernel version management and vulnerability scanning procedures to detect and remediate similar issues before they can be exploited in production environments. The patch dependencies indicate that this fix builds upon previous work to add list flush functionality for garbage collection cancellation, demonstrating the incremental nature of kernel security improvements in complex subsystems.