CVE-2024-27397 in Linux
Summary
by MITRE • 05/14/2024
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_tables: use timestamp to check for set element timeout
Add a timestamp field at the beginning of the transaction, store it in the nftables per-netns area.
Update set backend .insert, .deactivate and sync gc path to use the timestamp, this avoids that an element expires while control plane transaction is still unfinished.
.lookup and .update, which are used from packet path, still use the current time to check if the element has expired. And .get path and dump also since this runs lockless under rcu read size lock. Then, there is async gc which also needs to check the current time since it runs asynchronously from a workqueue.
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Analysis
by VulDB Data Team • 09/19/2025
The vulnerability identified as CVE-2024-27397 resides within the Linux kernel's netfilter subsystem, specifically affecting the nftables implementation that governs packet filtering and manipulation. This flaw represents a race condition scenario that could potentially allow malicious actors to exploit timing inconsistencies during set element operations, particularly when elements are being added, modified, or removed from nftables sets. The issue manifests when control plane transactions process set elements concurrently with garbage collection mechanisms, creating opportunities for inconsistent state management and potential bypass of intended access controls.
The technical root cause involves the absence of proper timestamp coordination between different execution paths within the nftables subsystem. Prior to the fix, the system relied on current time checks for various operations including lookup and update functions that execute in packet processing paths, while the garbage collection mechanism operated asynchronously using workqueues. This inconsistency created a window where set elements could theoretically expire during ongoing control plane transactions, leading to unpredictable behavior where elements might be prematurely removed or remain accessible beyond their intended timeout periods.
The fix implements a comprehensive timestamping mechanism that establishes a consistent reference point at the beginning of each transaction, storing this timestamp within the nftables per-network namespace area. This approach ensures that all relevant operations within the same transaction use the same temporal reference, preventing premature expiration of set elements during active processing. The implementation updates the set backend methods including insert, deactivate, and sync garbage collection paths to utilize this transaction timestamp rather than current time values. However, the solution maintains the use of current time for packet processing paths and dump operations to preserve performance characteristics and avoid introducing latency in critical packet handling code paths.
The operational impact of this vulnerability extends beyond simple access control bypasses, potentially affecting network security policies that rely on time-based set element expiration for dynamic rule management. Attackers could exploit this race condition to maintain persistent access to network resources by ensuring that set elements remain active longer than intended, or conversely cause legitimate security policies to fail by prematurely expiring elements during critical operations. This vulnerability directly relates to CWE-362, which describes concurrent execution use of a resource, and aligns with ATT&CK technique T1070.006 for Indicator Removal on Host, as the inconsistent behavior could mask malicious activities through manipulated set expiration timing.
Network administrators should prioritize patching systems running affected kernel versions, particularly those implementing complex nftables policies with time-based set management. The fix maintains backward compatibility while introducing robust timestamp coordination that prevents the race condition without compromising the performance characteristics essential for high-throughput network filtering operations. Organizations relying on dynamic nftables policies for access control, rate limiting, or temporary rule management should verify their configurations after applying the patch to ensure proper element lifecycle management continues to function as expected. The solution demonstrates proper kernel security practices by addressing the root cause through coordinated timestamp management rather than implementing broad mitigations that could impact system performance or functionality.