CVE-2026-97995 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
virtio_console: do not free control-out buffers on remove
__send_control_msg() publishes &portdev->cpkt as the control-out virtqueue cookie. remove_vqs() walks every virtqueue and passes leftover cookies to free_buf(), which treats them as struct port_buffer and reads sgpages.
If a control message is still on c_ovq when the device is unbound, free_buf() reads past the ports_device object.
KASAN reported slab-out-of-bounds in free_buf():
free_buf remove_vqs virtcons_remove unbind_store
The object was the ports_device allocated in virtcons_probe().
Drain c_ovq without freeing. The packet lives in portdev and is released with it.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified within the Linux kernel's virtio_console subsystem represents a critical memory safety flaw rooted in improper resource management during device unbinding operations. Specifically, this issue manifests as an out-of-bounds read that can lead to system instability or potential information disclosure depending on the state of memory at the time of exploitation. The core technical failure occurs within the interaction between the control-out virtqueue and the buffer cleanup routines when a virtual console device is removed from the system. Under normal operation, the function __send_control_msg() publishes the address of portdev->cpkt as the cookie associated with the control-out virtqueue to track pending control messages. However, during the teardown phase triggered by remove_vqs(), the kernel iterates through all active virtqueues and attempts to reclaim any leftover buffers by passing their cookies to free_buf(). This function assumes that every cookie corresponds to a valid struct port_buffer object allocated for data transmission.
When a device is unbound while there are still pending control messages residing in the c_ovq (control output queue), this assumption breaks down catastrophically. The cookie passed to free_buf() at this stage points not to an allocated port_buffer structure, but rather to the static cpkt member within the ports_device object itself. Because free_buf() interprets this pointer as a struct port_buffer, it proceeds to access fields such as sgpages which are located beyond the boundaries of the actual control packet structure. This results in a slab-out-of-bounds read where the kernel attempts to dereference memory addresses that do not belong to the intended object allocation. The vulnerability is triggered through a specific call chain involving free_buf being invoked by remove_vqs, which is called during virtcons_remove, ultimately initiated via unbind_store when an administrator or hypervisor removes the device from the virtual machine configuration.
From a security perspective, this flaw aligns with CWE-125, Out-of-bounds Read, as it involves accessing memory beyond the allocated buffer boundaries. The operational impact of such a vulnerability is severe in the context of cloud computing and virtualization environments where virtio devices are prevalent. An attacker who can influence the timing of device unbinding or manipulate the state of pending control messages could potentially trigger this out-of-bounds read to leak kernel memory contents into user space or cause a denial of service through a kernel panic triggered by invalid memory access detected by protections like KASAN (Kernel Address Sanitizer) in debug builds, or silent corruption leading to system crashes. In ATT&CK terms, this vulnerability facilitates techniques related to Discovery and potentially Defense Evasion if the leaked information aids further exploitation within the host environment. The risk is heightened because virtio_console devices are commonly used for inter-VM communication, meaning a compromised guest could theoretically leverage this flaw to probe the hypervisor or other guests sharing the same physical resources if isolation mechanisms fail due to kernel instability.
The resolution implemented in the Linux kernel addresses this issue by modifying the behavior of the removal process to explicitly drain the control-out queue without attempting to free its associated buffers as standard data packets. Since the control packet cpkt is statically allocated within the portdev structure, it does not require individual deallocation via free_buf(). Instead, the fix ensures that any pending messages in c_ovq are drained and discarded safely during the unbind process, allowing the entire ports_device object to be released cleanly when virtcons_remove completes. This approach eliminates the erroneous interpretation of control message pointers as data buffer cookies. To mitigate similar risks in broader systems, administrators should ensure their kernels are updated with this patch. Furthermore, developers working on virtualization drivers must adhere strictly to resource lifecycle management principles, ensuring that cleanup routines correctly distinguish between dynamically allocated buffers and statically managed structures within device contexts. Regular auditing of virtqueue handling code against CWE-416, Use After Free, and related memory safety standards is recommended to prevent analogous flaws in other subsystems.