CVE-2026-74642 in Linux
Summary
by MITRE • 08/22/2026
In the Linux kernel, the following vulnerability has been resolved:
ALSA: usb: Fix UAF at delayed release of MIDI2 EPs
The recent fix for UAF in ump_to_endpoint() caused another UAF because it tries to dereference the UMP endpoint object, but this might be executed at a delayed context where the endpoint has been already released.
Add private_free to clear the associated data for avoiding the further dereference for delayed releases.
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Analysis
by VulDB Data Team • 08/22/2026
The Linux kernel's Advanced Linux Sound Architecture (ALSA) subsystem contains a critical memory safety vulnerability within its USB MIDI2 driver implementation, specifically involving the handling of Unified MIDI Protocol endpoints. This issue manifests as a Use-After-Free condition that arises during the delayed release phase of endpoint objects. The root cause lies in an incomplete remediation strategy for a previously identified flaw. A prior patch attempted to address a similar use-after-free vulnerability within the ump_to_endpoint function by modifying how endpoint references were managed. However, this fix inadvertently introduced a new regression because it retained logic that dereferences UMP endpoint structures even when executed in delayed contexts where those objects may have already been deallocated and freed from memory.
From a technical perspective, the flaw occurs because the kernel attempts to access or manipulate data associated with an endpoint object after its reference count has dropped to zero and the underlying memory has been returned to the system allocator. In asynchronous or deferred execution paths common in USB driver frameworks, timing discrepancies can lead to race conditions where cleanup routines execute concurrently with ongoing operations that still hold stale pointers. When the delayed release routine runs, it assumes the endpoint object is valid, but due to prior deallocation triggered by other threads or interrupt handlers, this assumption fails. Dereferencing a freed pointer leads to undefined behavior, which typically results in kernel panics, system crashes, or potential data corruption depending on how quickly the memory region is reused for unrelated allocations.
The operational impact of this vulnerability includes significant stability risks for systems relying on USB MIDI2 devices. An attacker with local access could potentially trigger these delayed release conditions through specific sequences of device connection and disconnection events, combined with rapid audio stream manipulation or endpoint configuration changes. This could lead to denial-of-service scenarios by crashing the kernel. Furthermore, in more sophisticated attack vectors involving memory corruption exploitation techniques, a use-after-free condition can be leveraged to achieve arbitrary code execution if an attacker can control the contents of the freed memory region and predict its reallocation pattern. Such exploits allow for privilege escalation from user space to ring zero, compromising the entire system's integrity and confidentiality.
This vulnerability aligns with CWE-416, Use After Free, which describes situations where a program continues to use a pointer after it has been freed, leading to unpredictable behavior. In terms of threat modeling and attack frameworks, this flaw relates to MITRE ATT&CK technique T1059, Command and Scripting Interpreter, as the underlying memory corruption could facilitate subsequent code execution steps. It also touches upon T1203, Exploitation for Client Execution, if triggered via malicious USB device emulation that forces specific driver states. The vulnerability highlights the complexity of managing object lifecycles in asynchronous kernel environments where reference counting and deferred work queues must be meticulously synchronized to prevent temporal logic errors.
To mitigate this risk, developers have implemented a fix by introducing a private_free callback mechanism within the endpoint structure management code. This addition ensures that all associated data structures are explicitly cleared before the endpoint object is fully released from memory. By nullifying pointers or resetting state variables during the finalization phase, the driver prevents subsequent delayed operations from accessing invalid memory addresses. System administrators and users should ensure their Linux kernels are updated to versions containing this specific ALSA USB MIDI2 patch. Regular kernel updates are essential as they incorporate these critical memory safety corrections that close gaps left by previous partial fixes. Additionally, auditing custom or out-of-tree drivers for similar patterns of deferred dereferencing can help prevent analogous vulnerabilities in other subsystems.