CVE-2026-64490 Overview
CVE-2026-64490 is a Linux kernel vulnerability in the ALSA virtio-snd driver. The driver trusts control metadata returned by the virtio sound device without validation. A malicious or buggy device can advertise an invalid control type or an oversized value count, leading to out-of-bounds memory access in the guest kernel. The flawed metadata is used to index the g_v2a_type_map[] array in virtsnd_kctl_info() and to size loops and memcpy() operations in virtsnd_kctl_get() and virtsnd_kctl_put() against fixed-size virtio_snd_ctl_value and snd_ctl_elem_value buffers.
Critical Impact
A compromised or malicious virtio-snd device can trigger out-of-bounds reads and writes in the Linux guest kernel, enabling potential privilege escalation, memory corruption, or denial of service.
Affected Products
- Linux kernel versions containing the virtio-snd (ALSA virtio) driver prior to the fixing commits
- Guest Linux systems running under hypervisors that expose a virtio sound device
- Stable kernel branches referenced by commits 21584672fd69, 3243563f99ef, 5da9742de22d, and c77a6cbb36ff
Discovery Timeline
- 2026-07-25 - CVE-2026-64490 published to NVD
- 2026-07-27 - Last updated in NVD database
Technical Details for CVE-2026-64490
Vulnerability Analysis
The vulnerability resides in the virtio sound control-handling logic within the Linux kernel ALSA subsystem. The virtio-snd driver retrieves control metadata, specifically the control type and value count, directly from the paravirtualized device without sanity checks. This trust boundary violation lets device-supplied values drive kernel array indexing and memory copy sizing.
In virtsnd_kctl_info(), the device-supplied control type is used to index the g_v2a_type_map[] lookup table. An out-of-range type value reads memory outside the map. In virtsnd_kctl_get() and virtsnd_kctl_put(), the device-supplied value count sizes iteration and memcpy() operations targeting the fixed-size virtio_snd_ctl_value and snd_ctl_elem_value structures. An inflated count overflows those buffers.
The fix moves validation of both fields into virtsnd_kctl_parse_cfg(), rejecting invalid metadata before any enumerated items are queried or the control is exposed to ALSA userspace.
Root Cause
The root cause is missing input validation of device-provided data across a trust boundary. The driver treated the virtio device as trusted and used its metadata directly for array indexing and buffer sizing. This pattern is a classic out-of-bounds read/write condition caused by improper validation of untrusted input.
Attack Vector
Exploitation requires a malicious or compromised virtio sound device attached to the guest kernel. This scenario is relevant in confidential-computing and untrusted-hypervisor threat models, where the guest must defend against a hostile host or device emulator. It also applies when a userspace VMM component controlling virtio devices is compromised. The attacker crafts virtio-snd control descriptors with either an invalid type field or a count exceeding the fixed ALSA structure bounds.
No verified public exploit code is available. See the upstream fix commits for technical details: kernel.org commit 21584672fd69, commit 3243563f99ef, commit 5da9742de22d, and commit c77a6cbb36ff.
Detection Methods for CVE-2026-64490
Indicators of Compromise
- Guest kernel oops, panic, or KASAN reports referencing virtsnd_kctl_info, virtsnd_kctl_get, or virtsnd_kctl_put
- Unexpected slab-out-of-bounds or global-out-of-bounds messages tied to g_v2a_type_map or snd_ctl_elem_value
- Guest VM crashes or reboots correlated with attachment of a virtio-snd device
Detection Strategies
- Enable CONFIG_KASAN on kernels used for testing and fuzzing of the virtio-snd code path
- Fuzz the virtio-snd control interface from a controlled malicious device to surface OOB accesses before deployment
- Audit running kernels against the fixing commit hashes to confirm patch presence in the sound/virtio/ tree
Monitoring Recommendations
- Forward guest dmesg and journald kernel logs to a centralized data lake for anomaly detection on ALSA and virtio subsystems
- Alert on repeated guest crashes or ALSA driver faults across a virtualization fleet, which may indicate a compromised host emulator
- Track kernel package versions across the fleet and flag hosts running kernels prior to the fix
How to Mitigate CVE-2026-64490
Immediate Actions Required
- Update the Linux kernel to a version that includes the upstream fix commits for virtsnd_kctl_parse_cfg() validation
- Prioritize patching guests in confidential-computing deployments or environments where the hypervisor is not fully trusted
- Inventory all guest images that load the virtio_snd module and schedule reboots after kernel updates
Patch Information
The fix validates control type and value count once in virtsnd_kctl_parse_cfg() before querying enumerated items or exposing the control to ALSA. Apply the upstream patches from the stable tree: 21584672fd69, 3243563f99ef, 5da9742de22d, and c77a6cbb36ff. Distribution vendors are expected to backport these commits into supported kernel packages.
Workarounds
- Unload or blacklist the virtio_snd module on guests that do not require virtualized audio
- Remove or disable virtio sound device emulation in the hypervisor configuration for affected guests
- Restrict which workloads run on hosts using untrusted or third-party virtio-snd device emulators
# Blacklist the virtio_snd module until the kernel is patched
echo 'blacklist virtio_snd' | sudo tee /etc/modprobe.d/blacklist-virtio-snd.conf
sudo rmmod virtio_snd 2>/dev/null || true
sudo update-initramfs -u
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
