CVE-2026-90344 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: mac80211: disconnect on CSA to channel 0
The refactor for the CSA parsing erroneously equates channel zero and no information present, leading it to ignore a CSA on an AP that advertises a switch to that (invalid) channel. This leads to not disconnecting, which we should. For Intel devices, this can lead to a firmware crash.
Fix this by using an int type for the channel number as well as the opclass, and using a (negative) value that cannot be encoded in the element to indicate it's not present.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified within the Linux kernel’s mac80211 subsystem represents a critical logic error in the handling of Channel Switch Announcement frames during Wi-Fi operations. Specifically, this issue arises from an erroneous refactor that incorrectly equates channel zero with the absence of information. In IEEE 802.11 standards, a Channel Switch Announcement is used by an Access Point to notify associated stations of an impending change in operating channel. The flaw causes the kernel to ignore such announcements when they indicate a switch to channel zero, which is technically invalid and should trigger a disconnection rather than being treated as null data. This misinterpretation stems from using unsigned types or default values that fail to distinguish between a valid but erroneous instruction and missing metadata, leading to a state where the station remains connected despite receiving an unprocessable command from the network infrastructure.
The operational impact of this vulnerability is significant, particularly regarding system stability and security posture. When a device fails to disconnect upon receiving a CSA for channel zero, it may continue attempting communication on a non-existent or invalid frequency. For Intel wireless devices specifically, this state can precipitate firmware crashes due to undefined behavior in the hardware driver stack when processing these malformed instructions. From a broader perspective, this flaw undermines the reliability of network connectivity and exposes systems to potential denial-of-service conditions through automated exploitation where malicious actors could craft specific beacon frames or CSA elements to induce instability. Furthermore, remaining connected on an invalid channel prevents proper roaming and reassociation procedures, effectively isolating the device from legitimate network services while maintaining a false sense of connection status.
From a technical remediation standpoint, the fix involves modifying the data types used for storing channel numbers and operating classes within the mac80211 codebase to signed integers rather than unsigned or default-initialized values. By utilizing negative values that cannot be encoded in standard 802.11 elements, the kernel can reliably distinguish between a valid channel specification and the absence of one. This ensures that any CSA indicating an invalid channel triggers the appropriate disconnection logic immediately. This change aligns with robust input validation practices where edge cases like zero or negative values are explicitly handled to prevent logical bypasses in protocol parsers.
This vulnerability maps directly to CWE-20, which covers Improper Input Validation, as the system failed to correctly validate and interpret incoming channel switch parameters. Additionally, it relates to CWE-841, Improvement of Insufficient Enforcement of Validations for Inconsistent States, because the device remained in a connected state despite receiving contradictory or invalid network instructions. From an offensive security perspective, this behavior could be leveraged within ATT&CK technique T1499, Endpoint Denial of Service, by forcing firmware crashes on vulnerable Intel-based endpoints through crafted wireless frames. Mitigation requires applying kernel updates that incorporate the signed integer conversion and proper disconnection logic for invalid channel switches to restore stable network operation and prevent potential remote exploitation leading to system instability.