CVE-2026-98958 in Linux
Summary
by MITRE • 10/23/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: mt76: account non-AQL frames per peer rather than per link
The driver increments wcid->non_aql_packets when a frame goes to the hardware queue. The completion path decrements the counter again.
For an MLO peer, the hardware reports the completion on the link that it used for the transmission. This link can differ from the link that the driver queued the frame on. In that case, the increment and the decrement go to different link wcids, and the count drifts upwards until it blocks the station.
Keep the count on the wcid of the primary link, like the other peer-wide state.
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Analysis
by VulDB Data Team • 10/23/2026
The vulnerability identified in the Linux kernel's mt76 wireless driver represents a logic error within the handling of Multi-Link Operation (MLO) peers, specifically concerning how non-Aggregation Queue Limit frames are tracked across multiple network links. In modern Wi-Fi standards such as IEEE 802.11be, MLO allows a station to establish connections over multiple frequency bands or channels simultaneously to improve throughput and reliability. The mt76 driver manages these multi-link peers by maintaining per-peer state information, including counters for non-AQL packets which are used to enforce queue limits and prevent buffer exhaustion.
The technical flaw arises from an inconsistency in how packet counts are incremented versus decremented when frames traverse different links within the same MLO peer context. When a frame is queued for transmission, the driver increments a counter associated with the specific link's Wireless Context Identifier (WCID). However, upon hardware completion of that transmission, the wireless hardware reports the result on the actual physical link used for the transmission, which may differ from the logical link where the frame was originally queued. Consequently, the decrement operation targets a different WCID than the increment operation. This mismatch causes the counter associated with the original queueing link to remain artificially high because it never receives its corresponding decrement signal.
This discrepancy leads to a gradual drift in the packet count values for specific links within an MLO peer structure. As more frames are transmitted over differing links, the un-decremented counters accumulate indefinitely. Once these inflated counts exceed predefined thresholds intended to limit buffer usage and manage congestion, the driver incorrectly determines that the station has exceeded its quota. This erroneous state triggers a protective mechanism that blocks further communication with the affected station, effectively causing a denial of service for that specific peer despite adequate actual resource availability.
From a security perspective, this vulnerability aligns with CWE-682 Incorrect Calculation and CWE-367 Time-of-check to Time-of-use (TOCTOU) race conditions in state management, as it involves inconsistent updates to shared or related state variables under concurrent multi-link operations. In the context of the MITRE ATT&CK framework for enterprise security, this behavior can be categorized under T1499 Endpoint Denial of Service due to resource exhaustion logic errors. While not directly exploitable by an external attacker for remote code execution, it poses a significant risk to network stability and availability, particularly in high-throughput environments where MLO is actively utilized.
The resolution involves refactoring the counter management logic to ensure consistency across all links belonging to a single peer. By keeping the non-AQL packet count on the WCID of the primary link rather than distributing it per individual link, the driver ensures that increments and decrements always target the same state variable regardless of which physical link handles the transmission or completion reporting. This approach aligns with other peer-wide state management practices within the driver, ensuring accurate accounting of resource usage.
To mitigate this issue in affected systems, administrators should apply the latest kernel updates provided by their distribution vendors that include the patch for the mt76 driver's MLO handling logic. For environments relying on specific hardware configurations prone to link switching during transmission completion, monitoring network stability and checking for unexpected station disconnections can serve as an indicator of this flaw in older unpatched versions. Regular maintenance of wireless drivers is essential to prevent such logical errors from impacting operational continuity in multi-link Wi-Fi deployments.