CVE-2026-23272 in Linux
Summary
by MITRE • 03/20/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: unconditionally bump set->nelems before insertion
In case that the set is full, a new element gets published then removed without waiting for the RCU grace period, while RCU reader can be walking over it already.
To address this issue, add the element transaction even if set is full, but toggle the set_full flag to report -ENFILE so the abort path safely unwinds the set to its previous state.
As for element updates, decrement set->nelems to restore it.
A simpler fix is to call synchronize_rcu() in the error path. However, with a large batch adding elements to already maxed-out set, this could cause noticeable slowdown of such batches.
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Analysis
by VulDB Data Team • 05/23/2026
The vulnerability identified as CVE-2026-23272 resides within the Linux kernel's netfilter subsystem, specifically in the nf_tables module responsible for managing network packet filtering and manipulation. This issue represents a critical race condition and memory management flaw that can lead to system instability and potential security implications. The vulnerability manifests when handling set operations within the netfilter framework where elements are added to collections that have already reached their maximum capacity. The problem stems from improper handling of element insertion operations when sets are at full capacity, creating a scenario where the system attempts to publish elements before properly accounting for the existing state.
The technical flaw involves an improper sequence in the element insertion process where the set->nelems counter is incremented unconditionally before checking if the set has reached its maximum capacity. This premature increment creates a race condition where elements may be published to the set structure before proper validation occurs. When a set is full and the insertion operation fails, the system attempts to remove the newly added element without waiting for the required RCU (Read-Copy-Update) grace period. This allows RCU readers to potentially access memory that has been freed or modified, creating a classic use-after-free scenario that can lead to memory corruption and system crashes.
The operational impact of this vulnerability extends beyond simple system instability to potentially enable privilege escalation and denial of service conditions within network filtering operations. Attackers could exploit this vulnerability by carefully crafting network traffic patterns that trigger the race condition during element insertion operations, potentially leading to kernel memory corruption. The vulnerability affects systems heavily dependent on netfilter and nftables for packet filtering, which are commonly used in enterprise firewalls, network security appliances, and containerized environments where network policy enforcement is critical. The performance implications are particularly severe when dealing with large batch operations, as the suggested alternative fix of calling synchronize_rcu() in error paths could cause significant slowdowns during bulk element additions to already maxed-out sets.
The resolution implemented addresses this vulnerability by modifying the transaction handling logic to ensure proper state management even when sets are full. The fix introduces a more sophisticated approach where element transactions are still created even when the set is at maximum capacity, but with the set_full flag properly toggled to return -ENFILE to the abort path. This ensures that the set can safely unwind to its previous state without leaving the system in an inconsistent condition. For element updates, the solution properly decrements the set->nelems counter to maintain proper accounting. This approach follows established security principles and aligns with the CWE-362 weakness category for race conditions, while also addressing the ATT&CK technique T1068 for privilege escalation through kernel vulnerabilities. The solution maintains system performance by avoiding the costly synchronize_rcu() calls during error paths, instead relying on proper transaction management and state restoration mechanisms that prevent the race condition without significant performance degradation. This fix represents a robust approach to kernel security that balances correctness with performance considerations while maintaining the integrity of the netfilter subsystem's data structures.