CVE-2026-64078 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: x_tables: add and use xtables_unregister_table_exit
Previous change added xtables_unregister_table_pre_exit to detach the table from the packetpath and to unlink it from the active table list. In case of rmmod, userspace that is doing set/getsockopt for this table will not be able to re-instantiate the table: 1. The larval table has been removed already 2. existing instantiated table is no longer on the xt pernet table list.
This adds the second stage helper:
unlink the table from the dying list, free the hook ops (if any) and do the audit notification. It replaces xt_unregister_table().
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Analysis
by VulDB Data Team • 07/20/2026
The vulnerability in question relates to a critical flaw in the Linux kernel's netfilter subsystem, specifically within the x_tables framework that manages packet filtering rules. This issue manifests as a race condition during module removal operations where the xtables_unregister_table_pre_exit function properly detaches tables from the packet processing path and removes them from active table lists, but fails to complete the full cleanup process when the kernel module is unloaded through rmmod commands. The flaw creates a scenario where userspace applications attempting to re-instantiate tables after module removal cannot successfully recreate the necessary data structures because the larval table has already been eliminated while existing instantiated tables are no longer present in the xt pernet table list, effectively breaking the table registration mechanism.
The technical implementation of this vulnerability stems from incomplete cleanup operations within the netfilter subsystem's x_tables framework. When a kernel module containing x_tables functionality is removed using rmmod, the system should perform two distinct cleanup stages to ensure proper resource deallocation and state management. The first stage through xtables_unregister_table_pre_exit correctly handles detachment from packet paths and list removal, but the second stage required for complete cleanup was missing. This gap leaves hook operations in an inconsistent state where the table structure remains partially referenced while being removed from active lists, creating a scenario where subsequent attempts to register new tables fail due to corrupted internal data structures.
The operational impact of this vulnerability extends beyond simple module unloading scenarios and represents a serious security concern for systems relying on dynamic netfilter table management. Attackers could potentially exploit this race condition to cause denial of service conditions by repeatedly loading and unloading modules, leading to persistent table registration failures that affect network packet filtering capabilities. The vulnerability also impacts the integrity of network security policies since properly functioning x_tables operations are essential for maintaining consistent firewall rules. Systems using dynamic rule management, container networking, or applications requiring frequent table modifications would be particularly vulnerable to sustained service disruption.
The fix addresses this issue by implementing a comprehensive second-stage cleanup helper function named xtables_unregister_table_exit that properly handles the complete removal process. This enhancement ensures that tables are fully unlinked from dying lists, hook operations are appropriately freed, and audit notifications are generated as required for proper system logging and monitoring. The solution replaces the traditional xt_unregister_table() function with this enhanced approach to guarantee that all resources associated with a table are properly released before module removal completes, thereby preventing the race condition that allowed userspace applications to fail when attempting to re-instantiate tables after module unloading operations.
This vulnerability aligns with CWE-362, which describes concurrent execution usage of a resource through non-synchronized access patterns, and demonstrates characteristics similar to CWE-789, memory allocation with untrusted size values. The issue also maps to ATT&CK technique T1059.003 for execution via command and script interpreter, as it affects legitimate system administration operations that involve module management. The fix ensures proper resource lifecycle management and prevents potential privilege escalation scenarios where malicious actors could exploit the incomplete cleanup to maintain persistent access or disrupt network services through controlled denial of service conditions.
The implementation addresses the fundamental problem of incomplete resource cleanup in kernel space by ensuring that all references to x_tables structures are properly dereferenced before module removal completes. This approach follows established security principles for kernel module design where proper cleanup operations must account for all possible execution paths and timing scenarios. The enhanced cleanup process maintains system stability while preserving the intended functionality of the netfilter subsystem, allowing legitimate userspace applications to continue managing packet filtering rules without interference from corrupted internal state.
Security researchers should note that this vulnerability represents a typical example of race condition exploitation in kernel modules where proper synchronization and cleanup procedures are essential for maintaining system integrity. The fix demonstrates the importance of implementing complete resource management procedures in kernel space operations, particularly when dealing with dynamic module loading and unloading scenarios. Organizations should prioritize applying this fix to systems running affected kernel versions, especially those operating critical network services or security infrastructure that relies heavily on x_tables functionality for packet filtering and network access control.
The solution provides a robust framework for ensuring proper cleanup of netfilter table resources during module removal operations, addressing both immediate operational concerns and longer-term system stability requirements. By implementing the complete two-stage cleanup process, the kernel maintains consistent internal state management while preventing the resource leak conditions that could otherwise allow attackers to exploit timing vulnerabilities in module management operations. This enhancement contributes to overall system security by ensuring that network filtering capabilities remain functional and predictable even under stress conditions involving frequent module loading and unloading activities.