CVE-2026-74662 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
inet: frags: publish queues before arming timer
inet_frag_create() arms the fragment queue timer before inserting the queue into the fqdir rhashtable. If the namespace fragment timeout is zero or negative, the timer can run before the queue is published.
The timer callback then marks the queue complete, tries to remove a node that is not in the hash table yet, and drops the anticipated hash reference. Creation can subsequently publish the completed queue without restoring that reference, leaving a stale hash node after the caller drops the remaining reference.
Publish the queue first and arm the timer while holding the queue lock. This makes timer expiry wait until the queue is visible in the hash table, so inet_frag_kill() can remove the node and balance the hash reference.
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Analysis
by VulDB Data Team • 08/22/2026
The vulnerability identified within the Linux kernel networking subsystem involves a race condition during the initialization of IP fragment queues, specifically affecting the IPv4 stack implementation known as inet_frags. This issue stems from an incorrect ordering of operations in the inet_frag_create function where the expiration timer for a newly created fragment queue is armed before the queue structure is inserted into the global reassembly hash table, referred to internally as fqdir rhashtable. In normal operation, this sequence might not immediately cause visible issues because the window between arming the timer and publishing the queue is typically small. However, under specific configuration conditions where the namespace fragment timeout value is set to zero or a negative number, the kernel's internal logic may trigger immediate expiration of that timer before the insertion into the hash table completes. This creates a critical timing gap that allows for a race condition exploitable by local users with sufficient privileges to manipulate network namespaces or socket configurations.
When the timer expires prematurely due to the aforementioned configuration anomaly, the associated callback function inet_frag_kill is invoked while the fragment queue remains invisible in the global data structures. The callback attempts to mark the queue as complete and subsequently tries to remove its corresponding node from the hash table. Since the node has not yet been published or linked into the rhashtable, this removal operation fails silently or behaves unpredictably because there is no valid entry to unhash. Crucially, during the initial creation process, a reference count for the hash bucket was anticipated and taken but never properly released in this failure path. Consequently, when the inet_frag_create function finally proceeds to publish the queue into the hash table, it does so without restoring or balancing that expected hash reference. This results in an imbalance where the kernel retains a stale reference to a data structure that is either incomplete or improperly linked within the memory management subsystem of the network stack.
The operational impact of this flaw centers on resource exhaustion and potential denial of service conditions. The lingering stale hash node represents a memory leak, as the associated fragment queue structures are not properly freed due to the broken reference counting logic. Over time, particularly under high-volume fragmentation scenarios or when an attacker can trigger repeated creation of such queues through crafted packets, this leads to progressive kernel memory consumption. While immediate arbitrary code execution is unlikely given that the issue primarily affects internal bookkeeping rather than direct pointer manipulation in a way that allows control flow hijacking, the accumulation of these leaked structures can degrade system performance and eventually cause out-of-memory conditions within the network subsystem. This aligns with CWE-401, which describes memory leaks resulting from improper resource management, and specifically highlights issues related to reference counting errors where objects are not freed when they should be.
From a threat modeling perspective using the MITRE ATT&CK framework, this vulnerability can be categorized under T1496 Resource Hijacking, as an attacker could potentially leverage repeated exploitation of this race condition to consume system resources and degrade availability. It also touches upon CWE-362, Concurrent Execution Using Shared Resource with Improper Synchronization Race Conditions, due to the fundamental issue being a lack of proper synchronization between timer expiration events and data structure publication. The root cause is not a complex logic flaw but rather a simple ordering error in initialization routines that fails to account for edge cases involving timeout values.
To mitigate this vulnerability, it is essential to apply kernel updates provided by distribution vendors that address the specific patch correcting the order of operations within inet_frag_create. The fix involves publishing the fragment queue into the hash table before arming the expiration timer and ensuring that these actions are performed while holding the appropriate queue lock. This synchronization ensures that if a timer expires, the queue is already visible in the global tables, allowing the cleanup routine to correctly locate and remove the node from the hash structure, thereby properly balancing all reference counts. Administrators should ensure their systems are updated with the latest stable kernel versions available for their respective distributions. Additionally, monitoring network namespace configurations can help identify environments where fragment timeouts might be set to unusual values that could exacerbate this race condition, although applying the patch remains the primary and most effective remediation strategy.