CVE-2026-89728 in Linux
Summary
by MITRE • 09/11/2026
In the Linux kernel, the following vulnerability has been resolved:
i3c: renesas: Fix out-of-bounds access for newdevs mask
When software initiates DAA (Dynamic Address Assignment), the controller reports the result via the NRSPQP (Normal Response Queue Port Register). The data length field of the response descriptor, which is accessible through the NRSPQP register, indicates the number of devices remaining after DAA. Consequently, when the bus is empty, this field contains the maximum number of devices supported by the controller (8 for the Renesas I3C controller).
Adjust the condition that computes the newly discovered devices bitmask to prevent an out-of-bounds when the I3C bus is empty.
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Analysis
by VulDB Data Team • 09/11/2026
The vulnerability identified in the Linux kernel's i3c: renesas driver involves a critical out-of-bounds memory access triggered during the Dynamic Address Assignment process. This specific flaw resides within the handling of device discovery on Inter-Integrated Circuit (I2C) extensions for devices with Control capabilities, commonly known as I3C buses. The root cause stems from an incorrect logical condition used to compute the bitmask representing newly discovered devices. When software initiates DAA, a standard procedure in I3C bus management where unique addresses are assigned to connected slave devices, the hardware controller reports results via the Normal Response Queue Port Register (NRSPQP). This register contains response descriptors that include a data length field indicating the number of devices remaining after the assignment process.
The technical flaw arises from how this data length is interpreted when no new devices are found or when the bus state leads to an unexpected value in the descriptor. Specifically, if the I3C bus is empty or under certain edge conditions where no additional devices respond, the hardware may report a default maximum capacity rather than zero. For the Renesas I3C controller architecture, this maximum supported device count is eight. The driver code previously failed to adequately check whether this reported length exceeded valid bounds for its internal bitmask array before using it as an index or loop limit. Consequently, if the field contains the value eight due to the bus being empty or in a specific idle state, the software attempts to access memory locations beyond the allocated buffer size intended for tracking new devices. This results in an out-of-bounds read or write operation, depending on the exact implementation details of how the bitmask is manipulated immediately following this check.
From a security perspective, this vulnerability aligns with CWE-125, which describes Out-of-Bounds Read, and potentially CWE-787 if the logic leads to writing beyond buffer limits during subsequent processing steps. In terms of attack vectors, an attacker would need physical or logical access to the I3C bus infrastructure to trigger the DAA process under conditions that result in the erroneous reporting of device counts. While this is primarily a stability and reliability issue rather than a direct remote code execution vector, out-of-bounds accesses can lead to kernel panics, denial of service through system crashes, or potentially information disclosure if adjacent memory contents are leaked during the invalid read operation. The ATT&CK framework would categorize such exploitation under techniques involving resource exhaustion or local privilege escalation attempts via crash-induced instability, although direct exploitation for arbitrary code execution is less likely without further context on how the corrupted bitmask influences subsequent control flow.
The operational impact of this vulnerability includes system instability and potential denial of service when devices are enumerated on an I3C bus managed by Renesas hardware controllers. In embedded systems or industrial environments where these drivers are prevalent, a kernel crash can halt critical operations that rely on sensor data or peripheral communication over the I3C interface. Furthermore, if the out-of-bounds access corrupts adjacent kernel memory structures, it could theoretically lead to undefined behavior that compromises system integrity. Mitigation strategies involve applying the upstream Linux kernel patch that corrects the conditional logic governing the computation of the newly discovered devices bitmask. System administrators should ensure their kernels are updated to versions containing this fix. Additionally, developers integrating I3C drivers into custom embedded systems should verify that hardware-specific response descriptors are validated against expected bounds before being used for array indexing or loop iterations, adhering to defensive programming practices recommended by CWE-120 and related buffer overflow prevention guidelines.