CVE-2026-93271 in Linux
Summary
by MITRE • 09/24/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: ath11k: cap out-of-range rx MCS instead of leaving bogus rate
ath11k can receive HT/VHT/HE frames whose reported MCS is above the maximum that can be expressed in the corresponding mac80211 rate space (e.g. an HE frame reported with MCS 12, while HE tops out at MCS 11).
The frame itself is valid and decodes correctly, but for such a frame ath11k_dp_rx_h_rate() leaves rx_status->rate_idx set to the out-of-range value and never assigns rx_status->encoding, so it stays RX_ENC_LEGACY from the ath11k_dp_rx_h_ppdu() initialization. Once that frame reaches mac80211 it trips the rate sanity check and the frame is dropped with a splat:
ath11k_pci 0000:03:00.0: Received with invalid mcs in HE mode 12 WARNING: CPU: 0 PID: 0 at net/mac80211/rx.c:5433 ieee80211_rx_list+0xb0a/0xe90 [mac80211]
Dropping the frame would discard otherwise valid data, so instead cap the reported MCS to the maximum the rate space can express and deliver the frame. Set rx_status->encoding before the range check and assign rate_idx from the capped value, so a frame with an out-of-range MCS no longer leaves partial or bogus rate metadata behind. Also downgrade the logging level since they are not treated as invalid frames now. The only loss is that such a frame is reported as the capped MCS in the rx rate statistics.
Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.41
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Analysis
by VulDB Data Team • 09/24/2026
The Linux kernel driver for Qualcomm ath11k wireless adapters contains a logic flaw in the data path receive handler that fails to properly validate Modulation and Coding Scheme (MCS) indices received from hardware. Specifically, when processing High Efficiency (HE), HT, or VHT frames, the driver may encounter an MCS value reported by the firmware that exceeds the maximum index supported by the mac80211 rate space for that specific modulation type. For instance, HE mode supports MCS values up to 11, but hardware might report MCS 12 due to internal encoding nuances or edge cases in signal processing. While the frame payload itself is valid and decodes correctly at a lower level, the driver fails to clamp this value before passing it upstream to the mac80211 subsystem.
This oversight results in incomplete rate status metadata being passed up the stack. The function ath11k_dp_rx_h_rate() leaves the rx_status->rate_idx field set to the out-of-range integer and neglects to assign a valid encoding type, leaving it at the default RX_ENC_LEGACY value established during initialization. When mac80211 processes this frame in ieee80211_rx_list(), it performs sanity checks on the rate information. The combination of an invalid MCS index and incorrect encoding triggers these checks, causing the kernel to drop the packet and emit a warning splat indicating an invalid MCS was received in HE mode. This behavior effectively denies service for valid traffic under specific conditions where such out-of-range values are transmitted by peer devices or generated due to hardware quirks.
From a security perspective, this vulnerability represents a denial of service condition caused by improper input validation and boundary checking within the kernel network stack interaction layer. The flaw allows external wireless frames with non-standard but technically decodable parameters to crash the packet processing logic for that specific interface instance, leading to dropped packets and potential system instability if the warning triggers extensive logging or panic conditions depending on configuration. This aligns with CWE-20 Improper Input Validation as the driver fails to restrict input data to expected bounds before use. Furthermore, it relates to CWE-754 Improper Check for Unusual or Exceptional Conditions because the code does not handle edge cases in hardware-reported values gracefully. In terms of MITRE ATT&CK, this could be leveraged by an attacker sending crafted 802.11 frames to cause a denial of service against wireless connectivity services on affected systems.
The resolution involves modifying the ath11k driver to cap any reported MCS value that exceeds the maximum supported index for its modulation type down to that maximum valid limit before assigning it to rx_status->rate_idx. Additionally, the fix ensures that rx_status->encoding is correctly set prior to reaching mac80211's validation logic, thereby preventing the mismatch between rate index and encoding type. By handling these out-of-range values gracefully rather than discarding them, the driver preserves valid data transmission while maintaining system stability. The logging level for such events has also been downgraded since they are no longer treated as fatal errors but rather as normalized conditions. This approach ensures that frames with slightly non-standard MCS indices are processed correctly without triggering kernel warnings or dropping packets unnecessarily.