CVE-2026-80721 in Linux
Summary
by MITRE • 08/28/2026
In the Linux kernel, the following vulnerability has been resolved:
Bluetooth: ISO: ensure no dangling hcon references in iso_conn
After iso_conn_del(), ISO sockets should not dereference the hcon any more. Currently, clearing iso_conn::hcon relies on iso_conn_del() releasing the last reference to the iso_conn.
Simplify this by explicitly clearing conn->hcon in iso_conn_del(), to avoid more complex reasoning on races about who holds the last reference.
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Analysis
by VulDB Data Team • 08/28/2026
The Linux kernel Bluetooth subsystem contains a logic flaw within the Isochronous Sockets (ISO) implementation that can lead to use-after-free vulnerabilities and potential system instability. This issue specifically affects the handling of connection objects, represented by the hcon structure, during the lifecycle management of ISO connections. The vulnerability arises from an implicit dependency on reference counting mechanics rather than explicit state clearing, creating a window where dangling pointers may persist even after a connection has been logically terminated.
In the current implementation, when an ISO socket is deleted via iso_conn_del(), the system relies on the assumption that this function will release the final reference to the underlying hcon object. This approach requires complex reasoning about race conditions and concurrency to ensure that no other part of the kernel retains a pointer to the connection while it is being torn down. If there are any delays or asynchronous operations that hold references, or if the order of cleanup steps varies due to timing differences in multi-threaded environments, the hcon structure might be freed prematurely. Consequently, subsequent attempts by remaining code paths to access conn->hcon would result in dereferencing a pointer to memory that has already been returned to the allocator and potentially reused for other purposes.
This type of flaw is classified under CWE-416, Use After Free, as it involves accessing memory after it has been freed. From an offensive security perspective, such vulnerabilities can be leveraged through ATT&CK technique T1203, Exploitation for Defense Evasion or Command and Control, if the attacker can trigger the race condition to execute arbitrary code within kernel space. The impact of this vulnerability is significant because a successful exploit could allow an unprivileged local user to escalate privileges to root level by corrupting kernel memory structures. This corruption might lead to system crashes, denial of service, or more critically, the execution of malicious payloads with full control over the operating system.
The resolution involves simplifying the reference management logic within iso_conn_del(). Instead of relying on the implicit release of references through complex race-free assumptions, the fix explicitly clears conn->hcon immediately during the deletion process. This ensures that any subsequent access to the hcon field will encounter a null pointer or an invalid state rather than a dangling reference to freed memory. By making this clearing explicit and immediate, the kernel eliminates the ambiguity regarding which component holds the last reference, thereby preventing use-after-free scenarios regardless of timing variations in concurrent operations.
To mitigate risks associated with similar vulnerabilities in Linux-based systems, administrators should ensure that all security patches are applied promptly as they become available from distribution vendors. For developers maintaining Bluetooth stacks or other network subsystems, it is critical to adopt explicit nullification patterns when destroying objects rather than relying solely on reference counting semantics for safety checks. Regular code audits focusing on lifecycle management of kernel structures can help identify and prevent dangling pointer issues before they are deployed into production environments.