CVE-2026-80969 in Linux
Summary
by MITRE • 09/11/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: mpu401: Check card index validity at probe
mpu401 driver blindly trusts that the given devptr->id value is within the proper card index range at probe. It's OK for the devices the driver itself creates at the module probe time, but if the device is bound manually via sysfs interface, this could be -1 as "none", and this leads to OOB access for index[] and other parameters.
Add a sanity check for the card index and warn/correct it if it's a value out of the range.
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Analysis
by VulDB Data Team • 09/12/2026
The Linux kernel audio subsystem contains a critical input validation flaw within the MPU401 MIDI driver, specifically during the device probe phase. This vulnerability stems from an assumption that the hardware identifier provided by the system is always valid and falls within expected bounds for card indexing. Under normal circumstances, when the driver initializes devices it creates itself at module load time, this trust model holds true because the kernel infrastructure ensures proper initialization sequences. However, the security posture degrades significantly when a device is manually bound to the driver through the sysfs interface by an administrator or automated script. In such scenarios, if the specified card index does not correspond to an existing valid entry in the internal array structures, the value may default to negative one, indicating no available slot. The driver fails to perform any sanity checks on this input before proceeding with memory operations that rely on this index as a pointer offset or array subscript.
This lack of boundary checking leads directly to out-of-bounds access vulnerabilities within the kernel's memory space. When the invalid card index is used to access internal data structures such as the index array and other related parameters, it results in reading from or writing to memory locations that are outside the allocated boundaries for those specific arrays. This type of error falls squarely under CWE-125, which describes out-of-bounds read vulnerabilities, although depending on how the invalid value is utilized further down the execution path, it could also facilitate write operations leading to CWE-787, an out-of-bounds write vulnerability. The immediate technical consequence is memory corruption or unauthorized data exposure, as the kernel attempts to interpret garbage values from adjacent memory regions that do not belong to the intended audio card structures.
The operational impact of this flaw extends beyond simple application crashes and can compromise system stability and security integrity. An attacker with local access who possesses the ability to manipulate sysfs bindings could potentially trigger these out-of-bounds accesses repeatedly or in specific patterns to exploit undefined behavior within the kernel. While a single instance might result in a kernel panic causing a denial of service, more sophisticated exploitation techniques could leverage memory corruption to escalate privileges or execute arbitrary code. This aligns with ATT&CK technique T1059, Command and Scripting Interpreter, if used as part of a broader attack chain involving local privilege escalation via the audio subsystem's interaction points. The vulnerability highlights the risks associated with allowing user-space entities to influence kernel-level resource allocation without rigorous validation mechanisms in place.
To mitigate this risk, developers have implemented strict input validation logic within the probe function of the MPU401 driver. The fix introduces a sanity check that verifies whether the provided card index is within the valid range before any subsequent operations are performed on it. If an out-of-range value such as negative one is detected, the system now issues a warning and corrects or rejects the invalid input rather than proceeding with unsafe memory access patterns. This defensive programming approach ensures that only legitimate identifiers trigger resource allocation routines. System administrators should ensure their kernels are updated to include this patch, thereby closing the gap where manual device binding could previously lead to kernel instability or potential exploitation through improper index handling in the ALSA subsystem.