CVE-2026-98189 in Linux
Summary
by MITRE • 10/06/2026
In the Linux kernel, the following vulnerability has been resolved:
wifi: wilc1000: fix RX buffer OOB-write in wilc_wlan_handle_isr_ext()
wilc_wlan_handle_isr_ext() takes the RX transfer size from the device-reported interrupt status register (a 15-bit field shifted left by 2, up to 131068 bytes) and reads that many bytes from the device into rx_buffer, which is only WILC_RX_BUFF_SIZE (96K) large. The wrap check only handles the current offset; the size itself is never compared against the buffer, so a bogus SDIO device can make the driver OOB-write rx_buffer by up to ~32K with data it controls.
The oversized transfer also leaves rx_buffer_offset past the end of the buffer, after which the unsigned wrap check stops working and the overflow can repeat.
Drop any transfer whose size exceeds the RX buffer, acknowledging the data interrupt and re-arming the RX engine so the bogus frame is discarded and reception can continue. This also restores the rx_buffer_offset <= WILC_RX_BUFF_SIZE invariant the wrap check relies on.
This is not expected to change driver behavior in most cases: without this check, an oversized transfer would most likely corrupt neighboring kernel memory instead of completing anyway, and the drop path performs the same interrupt acknowledgment and RX engine re-arming as the normal path, so subsequent transfers are received unaffected.
Discovered by Atuin - Automated Vulnerability Discovery Engine.
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Analysis
by VulDB Data Team • 10/06/2026
The Linux kernel driver for the wilc1000 Wi-Fi chip contains a critical out-of-bounds write vulnerability within the interrupt handling routine named wilc_wlan_handle_isr_ext. This function is responsible for processing received data from the hardware device via an SDIO interface. The core of the flaw lies in how the transfer size is determined and validated before memory operations are performed. Specifically, the driver retrieves the RX transfer size directly from a 15-bit field within the device-reported interrupt status register. This value is shifted left by two bits to calculate the byte count, resulting in a potential maximum size of approximately 131068 bytes. However, the destination buffer, defined as rx_buffer with a fixed capacity of WILC_RX_BUFF_SIZE or 96 kilobytes, is significantly smaller than this theoretical maximum. The existing validation logic only checks for wrap-around conditions relative to the current offset within the buffer but fails to verify whether the total requested transfer size exceeds the physical boundaries of the allocated memory region.
This architectural oversight allows a malicious or malfunctioning SDIO device to trigger an out-of-bounds write by requesting a data transfer larger than 96 kilobytes. When such a request is processed, the driver proceeds to copy data from the hardware into rx_buffer without adequate bounds checking on the total size. Consequently, if the reported size exceeds the buffer capacity, the memcpy operation will overwrite memory locations immediately following the allocated buffer in kernel space. The vulnerability can result in an out-of-bounds write of up to approximately 32 kilobytes with data controlled by the external device. This scenario represents a classic CWE-787 Out-of-Bounds Write weakness, where insufficient validation of input values leads to memory corruption that compromises system integrity and stability.
The operational impact extends beyond simple buffer overflow due to state management issues within the driver logic. After an oversized transfer occurs, the internal variable rx_buffer_offset is left pointing past the end of the allocated buffer. The subsequent unsigned wrap check relies on this offset being within valid bounds to function correctly. Once the offset exceeds the buffer limit, the wrap-around detection mechanism ceases to operate as intended, potentially allowing repeated overflow conditions during subsequent interrupt handling cycles. This state corruption can lead to further memory degradation and unpredictable driver behavior, effectively creating a persistent vulnerability that persists across multiple data reception events until the device is reset or the module is unloaded.
From an attacker perspective, this flaw aligns with ATT&CK technique T1059 Command and Scripting Interpreter if exploited for code execution, but more directly it facilitates privilege escalation through memory corruption techniques such as heap spraying or overwriting kernel control structures like function pointers or object headers. An adversary controlling the SDIO bus could exploit this to execute arbitrary code in kernel space with root privileges. The discovery of this vulnerability was conducted using Atuin, an automated vulnerability discovery engine that utilizes symbolic execution and fuzzing techniques to identify logic errors in complex systems like operating system kernels.
The resolution involves modifying the wilc_wlan_handle_isr_ext function to implement strict size validation before initiating any data transfer operations. The patch introduces a check that compares the device-reported transfer size against the maximum allowable buffer size defined by WILC_RX_BUFF_SIZE. If the requested size exceeds this limit, the driver now discards the oversized frame rather than attempting to copy it into memory. Crucially, even when dropping the invalid frame, the driver correctly acknowledges the data interrupt and re-arms the RX engine. This ensures that normal reception processes can continue uninterrupted after a malicious or erroneous large transfer is rejected.
This fix restores the invariant that rx_buffer_offset must remain less than or equal to WILC_RX_BUFF_SIZE, thereby ensuring the reliability of subsequent wrap-around checks. In most operational scenarios, this change will not alter driver behavior because oversized transfers were previously causing memory corruption rather than successful completion. By explicitly dropping these frames and maintaining proper interrupt state management, the patch prevents both immediate buffer overflows and long-term state degradation. This approach exemplifies secure coding practices by validating external inputs against resource constraints before performing sensitive memory operations, thereby mitigating risks associated with CWE-20 Improper Input Validation and reducing the attack surface for kernel-level exploits.