CVE-2026-98423 in Linux
Summary
by MITRE • 10/14/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: mac80211_hwsim: don't hand frames to mac80211 while stopping
The code checks ->started for frames coming from wmediumd, but the radio can be stopped after the check and before frame delivery, causing mac80211 to hit the WARN_ON(!local->started).
Expand the mutex for this case and synchronise against it when the radio is stopped to avoid being able to hit the warning with hwsim.
Drop the error print that would've complicated the error path, it only triggers for allocation failures (already noisy) and malformed frames anyway.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified in the Linux kernel's mac80211_hwsim subsystem represents a classic race condition arising from improper synchronization between state checks and resource access. The hwsim module is designed to simulate wireless hardware behavior for testing purposes, allowing user-space applications like wmediumd to inject simulated radio frames into the networking stack. In this specific scenario, the code performs an initial check on the local interface's started status flag before attempting to hand a received frame over to the mac80211 subsystem. However, there exists a critical time-of-check-to-time-of-use gap where the wireless radio can be stopped by another thread or process after the initial validation but prior to the actual delivery of the frame. This lack of atomicity allows the system state to change unexpectedly during execution, leading to an inconsistent operational context that triggers a kernel warning condition indicating that mac80211 was invoked while the local interface was not in a started state.
From a technical perspective, this flaw is categorized under CWE-367, which describes Time-of-check Time-of-use (TOCTOU) race conditions. The root cause lies in the insufficient locking scope within the hwsim driver's frame reception path. By only checking the started flag without holding the appropriate mutex that governs the radio state transitions, the kernel exposes itself to a scenario where concurrent operations can invalidate assumptions made during the check phase. When the radio is stopped, it typically involves tearing down internal structures and resetting states, which conflicts with the expectation of mac80211 that it will receive valid frames from an active interface. The resulting WARN_ON condition serves as a safeguard against undefined behavior but indicates a significant logic error in the driver's concurrency control mechanisms.
The operational impact of this vulnerability is primarily centered on system stability and debuggability rather than direct remote code execution or privilege escalation, given that hwsim is generally used for testing and simulation purposes. However, triggering the WARN_ON condition can lead to kernel log spamming, which may obscure other critical security alerts or performance metrics in production environments relying on similar virtualization layers. In more severe cases, if the subsequent operations following the warning assume a valid state without further validation, it could potentially lead to use-after-free scenarios or null pointer dereferences, although the primary immediate effect is the assertion failure and potential denial of service through kernel panic depending on configuration settings for warnings. This aligns with ATT&CK technique T1499, Endpoint Denial of Service, as an attacker capable of interacting with hwsim could potentially disrupt system operations by repeatedly triggering this race condition.
To mitigate this vulnerability, the fix involves expanding the mutex lock to encompass both the state check and the frame delivery process, ensuring that these actions are performed atomically relative to radio stop events. By synchronizing access against a common lock when the radio is stopped, the driver prevents any new frames from being processed while the teardown sequence is in progress or pending completion. This ensures that once the started flag indicates an inactive state, no further frame handling can occur until the interface is explicitly restarted and re-initialized. Additionally, the removal of specific error prints for allocation failures and malformed frames simplifies the error path, reducing noise without compromising security posture since these conditions are already handled by broader logging mechanisms or result in immediate rejection of invalid input. This approach reinforces the principle of least privilege and strict state management within kernel subsystems to prevent race-induced inconsistencies.