CVE-2026-46207: Linux vsock/virtio Incomplete Payload Disclosure in Network Monitoring

Technical summary

The vulnerability exists in virtio_transport_build_skb() within the vsock/virtio subsystem. When processing non-linear socket buffers (skbs), the function calls virtio_transport_copy_nonlinear_skb() to mirror packet data to the vsockmon tap interface. This helper function manually constructs an iov_iter structure but fails to set the iov_iter.count field, which specifies the copy length. Since iov_iter is zero-initialized, the subsequent data copy operation transfers zero bytes, leaving the destination buffer uninitialized. The fix consolidates linear and non-linear code paths by using skb_copy_datagram_iter() with iov_iter_kvec(), matching the approach already in place within vhost-vsock, and adds error checking on the copy operation's return value.

Business impact

Organizations relying on vsockmon for network traffic analysis, debugging, or security monitoring will experience blind spots in their visibility. Virtual machine hosts and container platforms that depend on virtual socket monitoring for troubleshooting or compliance logging could miss critical data, potentially causing gaps in audit trails or hindering incident investigation. The incomplete payload delivery may complicate root-cause analysis of virtual networking issues and could allow malicious activity within virtual environments to evade detection by monitoring infrastructure.

Affected systems

The Linux kernel is affected, specifically systems running kernels with the vulnerable vsock/virtio code path. This includes virtualization hosts, container platforms, and any systems using virtual sockets for inter-process communication over virtio transport. The vulnerability requires local access and standard user-level privileges to trigger. Kernel versions prior to the patch are vulnerable; verify the specific affected versions against the vendor advisory.

Exploitability

Exploitation requires local access to the system and standard user privileges (CWE-401 indicates resource management issues). An attacker cannot trigger this remotely. The barrier to exploitation is low—any local process can create vsock connections that transit through the affected code path. However, the direct security impact is limited to visibility loss rather than code execution or privilege escalation; the vulnerability serves primarily as an information disclosure vector for those actively monitoring vsock traffic.

Remediation

Apply the kernel patch that consolidates the linear and non-linear buffer handling within virtio_transport_build_skb() to use skb_copy_datagram_iter() uniformly. This unified approach ensures iov_iter.count is properly initialized and that copy operations are error-checked. Verify the patched kernel version against the vendor advisory before deployment.

Patch guidance

Update the Linux kernel to a version incorporating the vsock/virtio fix. Consult the vendor advisory for specific patched versions and backport availability for your kernel branch. Test the update in a non-production environment to confirm compatibility with your virtualization or container infrastructure before rolling out to production systems.

Detection guidance

Monitor kernel version compliance against vendor advisories to identify unpatched systems. During incident investigation, note that vsockmon packet captures prior to the patch may be incomplete and should not be treated as a definitive record of all vsock traffic. Systems with custom monitoring or debugging reliant on vsockmon tap interfaces should be re-evaluated post-patch to ensure visibility restoration. Kernel build metadata can confirm whether a running kernel includes the fix.

Why prioritize this

This medium-severity vulnerability (CVSS 5.5) should be addressed during standard patch cycles but does not require emergency out-of-band updates in most environments. However, prioritize patching if your organization relies heavily on virtual socket monitoring for security compliance, debugging, or forensic analysis. The local-only requirement and need for user-level privileges reduce urgency compared to network-exploitable flaws, but the information disclosure aspect makes it relevant for defense-in-depth strategies in virtualized infrastructures.

Risk score, explained

CVSS 5.5 reflects medium severity: the vulnerability requires local access (AV:L) and standard user privileges (PR:L), ruling out remote or escalated exploitation vectors. The attack is straightforward once local access is obtained (AC:L), but the direct impact is limited to availability of monitoring data (A:H) with no confidentiality or integrity compromise of the system itself. The user-initiated trigger mechanism and localized scope prevent a higher score despite the certainty of the impact on monitoring visibility.

Frequently asked questions