CVE-2026-58091 in FreeBSD
Summary
by MITRE • 08/26/2026
The implementation of this ioctl attempts to acquire locks on all channels in a sync group. If locking a channel would block, it releases the sync group list lock and sleeps. Upon reawakening, it is possible that the sync group structure is freed, but the implementation did not handle this possibility.
On a system with a multiple audio devices, an unprivileged local user can exploit this use-after-free to escalate privileges.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability described involves a critical race condition within the Linux kernel's sound subsystem, specifically affecting the ioctl interface used for managing synchronization groups among audio channels. This functionality is primarily utilized by applications requiring precise timing and coordination across multiple audio devices or streams. The core technical flaw lies in the memory management logic during lock acquisition attempts. When an application requests to acquire locks on all channels within a specific sync group, the kernel implementation checks if locking any individual channel would cause the process to block due to contention with other processes holding those resources. If such blocking is anticipated, the current design dictates that the system should release the overarching sync group list lock and put the calling thread into a sleep state until the condition changes or it is woken up by another event.
The fundamental security defect arises from the failure of this implementation to verify the validity of the sync group structure after the process reawakens. In concurrent systems, particularly those with multiple audio devices where resource contention is frequent, there exists a narrow but exploitable window between the moment the thread sleeps and the moment it resumes execution. During this interval, another kernel context or user-space action can trigger the deallocation of the sync group structure if no other references to it are maintained securely. Because the code does not re-validate that the pointer to the sync group still points to a valid, allocated memory region upon waking up, it proceeds to dereference what is now a dangling pointer. This scenario constitutes a classic use-after-free vulnerability, where the kernel continues to operate on freed memory, leading to undefined behavior and potential control flow hijacking.
The operational impact of this flaw is severe due to its location within the kernel space and its accessibility from user space without requiring elevated privileges initially. An unprivileged local attacker can craft specific ioctl calls that trigger the locking mechanism under conditions designed to maximize the race window. By carefully timing their requests against other processes or system loads, they can force the synchronization group structure to be freed while their thread is asleep. Upon resumption, the kernel's attempt to access fields within this now-invalid memory structure allows for arbitrary read and write primitives. These primitives enable the attacker to overwrite critical kernel data structures, such as function pointers or security credentials, thereby achieving local privilege escalation from a standard user account to root-level administrative control over the system.
From an industry standards perspective, this vulnerability maps directly to CWE-416, which defines use-after-free errors where memory is accessed after it has been freed. The exploitation technique aligns with MITRE ATT&CK tactics related to Privilege Escalation on Linux systems, specifically leveraging kernel vulnerabilities to bypass user-level restrictions. Mitigating such issues requires a multi-layered approach within the operating system's development lifecycle. First, developers must implement robust reference counting mechanisms or use RCU (Read-Copy-Update) synchronization primitives that ensure memory is not freed while it might still be accessed by sleeping threads. Second, adding explicit validation checks after any sleep operation to confirm that the data structures being accessed remain valid and allocated can prevent dereferencing of dangling pointers. Additionally, enabling kernel hardening features such as KASAN (Kernel Address Sanitizer) during development phases helps in detecting these race conditions early before they reach production environments.