CVE-2026-90399 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: ath12k: fix stride mismatch in mac_phy_caps_parse()
Currently, in ath12k_wmi_mac_phy_caps_parse(), kzalloc() sizes the mac_phy_caps buffer as tot_phy_id * len, where len is clamped to min(firmware_len, sizeof(struct ath12k_wmi_mac_phy_caps_params)). The subsequent memcpy() destination advances by sizeof(full struct) per slot via C pointer arithmetic, not by the clamped len. When firmware sends short TLVs, the second and later slots are written past the end of the allocation.
The reader in ath12k_pull_mac_phy_cap_svc_ready_ext() also indexes the buffer with full-struct pointer arithmetic, so the allocation must match that stride.
Fix by using kzalloc_objs(), which derives the element size from the pointer type, making allocation size and pointer stride provably consistent regardless of what len the firmware provides.
Tested-on: WCN7850 hw2.0 PCI WLAN.HMT.1.1.c7-00108-QCAHMTSWPL_V1.0_V2.0_SILICONZ_UPSTREAM-3
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel's ath12k wireless driver represents a critical memory safety issue rooted in an incorrect calculation of buffer allocation sizes relative to pointer arithmetic strides. Specifically, within the function ath12k_wmi_mac_phy_caps_parse(), the system utilizes kzalloc() to allocate memory for a mac_phy_caps buffer based on a total phy ID count multiplied by a length variable that is clamped against either the firmware-provided length or the size of the struct ath12k_wmi_mac_phy_caps_params. This approach creates a fundamental mismatch because subsequent operations within the same function employ C pointer arithmetic to advance through the allocated memory, incrementing the destination address by the full sizeof(struct) for each slot rather than by the clamped len value. Consequently, when the firmware transmits truncated or short Type-Length-Value (TLV) structures that result in a smaller clamped length, the allocation size becomes insufficient to accommodate the larger stride used during data copying operations.
This discrepancy leads directly to an out-of-bounds write condition where the second and subsequent slots are written past the end of the allocated memory buffer. The risk is further compounded by the consumer side of this interaction, specifically in ath12k_pull_mac_phy_cap_svc_ready_ext(), which also indexes into the same buffer using full-struct pointer arithmetic. This means that not only does the initial write operation corrupt adjacent heap memory or trigger a kernel panic due to exceeding allocation boundaries, but any subsequent read operations relying on consistent indexing may also access invalid memory regions if the corruption has altered metadata or neighboring data structures. Such vulnerabilities are classified under CWE-120 Buffer Copy without Checking Size of Input and CWE-787 Out-of-bounds Write, reflecting both the failure to validate input sizes against buffer capacity and the resulting unauthorized modification of system memory.
From an operational perspective, this flaw poses significant risks to system stability and security. An attacker who can influence or manipulate the firmware communication stream could potentially exploit this out-of-bounds write to overwrite critical kernel data structures, leading to denial of service through immediate kernel crashes or more sophisticated attacks involving arbitrary code execution if specific memory layouts allow for control flow hijacking. The vulnerability highlights a common pitfall in low-level systems programming where manual size calculations are prone to errors when the stride used for iteration differs from the unit size assumed during allocation. In this case, relying on fixed-size assumptions without accounting for variable input lengths creates a predictable failure mode that can be triggered by malformed or maliciously crafted wireless management frames.
The resolution involves replacing the manual kzalloc() calculation with kzalloc_objs(), a kernel helper function designed to handle object array allocations safely. By deriving the element size directly from the pointer type, this fix ensures that the allocation size is provably consistent with the stride used in subsequent pointer arithmetic operations, regardless of the variable len value provided by the firmware. This change eliminates the possibility of mismatched strides and prevents out-of-bounds writes at the source. To mitigate similar risks in other parts of the codebase or future developments, developers should prioritize using type-safe allocation helpers that automatically calculate sizes based on element counts and types rather than manual multiplication with potentially variable lengths. Additionally, implementing strict bounds checking before any memcpy operation involving firmware data is essential to ensure that input does not exceed allocated boundaries. This incident underscores the importance of aligning memory management strategies with access patterns in kernel drivers handling external inputs from hardware or network sources.