CVE-2025-39718 in Linux
Summary
by MITRE • 09/05/2025
In the Linux kernel, the following vulnerability has been resolved:
vsock/virtio: Validate length in packet header before skb_put()
When receiving a vsock packet in the guest, only the virtqueue buffer size is validated prior to virtio_vsock_skb_rx_put(). Unfortunately, virtio_vsock_skb_rx_put() uses the length from the packet header as the length argument to skb_put(), potentially resulting in SKB overflow if the host has gone wonky.
Validate the length as advertised by the packet header before calling virtio_vsock_skb_rx_put().
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Analysis
by VulDB Data Team • 02/09/2026
The vulnerability CVE-2025-39718 represents a critical buffer overflow condition within the Linux kernel's virtual socket implementation, specifically affecting the vsock/virtio subsystem. This flaw exists in the handling of virtual socket packets received by guest operating systems in virtualized environments. The vulnerability stems from insufficient validation of packet metadata prior to memory allocation operations, creating a potential pathway for malicious actors to exploit memory corruption vulnerabilities. The issue is particularly significant in containerized environments and virtual machine deployments where vsock communication is prevalent, as it directly impacts the stability and security of virtualized networking components. The vulnerability affects systems utilizing virtio virtual socket drivers, commonly found in cloud computing platforms, virtualization solutions, and container orchestration environments where guest-to-host communication occurs through virtual socket interfaces.
The technical root cause of this vulnerability lies in the improper sequence of validation operations within the virtio vsock packet processing pipeline. When a guest system receives a vsock packet, the implementation validates only the virtqueue buffer size through the virtio_vsock_skb_rx_put() function but fails to verify the packet length field contained within the packet header itself. This oversight creates a scenario where malicious or malformed packets can contain an oversized length value that exceeds the actual buffer boundaries. The function subsequently passes this unvalidated length value directly to skb_put(), which performs memory allocation operations based on the potentially malicious length specification. This creates a classic buffer overflow condition where the kernel's socket buffer management system attempts to allocate more memory than available, leading to memory corruption that can be exploited for privilege escalation or system instability. The vulnerability manifests as a direct consequence of inadequate input validation and violates fundamental security principles of defensive programming and input sanitization.
The operational impact of CVE-2025-39718 extends beyond simple memory corruption, presenting significant risks to virtualized environments and cloud infrastructure. Attackers exploiting this vulnerability could potentially achieve privilege escalation within guest operating systems, leading to complete compromise of virtual machines and their underlying host systems. The vulnerability affects systems running kernel versions that include the affected vsock/virtio implementation, particularly those utilizing virtualization technologies such as KVM, Xen, or VMware ESXi where virtio drivers are employed for guest-to-host communication. In containerized environments using vsock for inter-container communication or service discovery, this vulnerability could enable attackers to break out of container boundaries and gain access to host resources. The impact is particularly severe in multi-tenant cloud environments where guest isolation is paramount, as successful exploitation could allow one tenant to compromise another tenant's virtual machines. Additionally, the vulnerability could be leveraged to cause denial of service conditions across virtualized infrastructure, potentially affecting entire data center operations.
Mitigation strategies for CVE-2025-39718 should focus on immediate patch application and implementation of additional security controls. The primary remediation involves applying the kernel patch that implements proper validation of packet header length fields before passing them to skb_put() operations, ensuring that the length values are within acceptable bounds relative to the actual packet data and buffer capacity. Organizations should prioritize patching all affected virtualization environments, particularly those running critical workloads or hosting sensitive data. Network segmentation and monitoring should be enhanced to detect anomalous vsock traffic patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-129 Input Validation and CWE-787 Out-of-bounds Write categories, representing a classic case of insufficient validation of externally provided data. From an ATT&CK perspective, this vulnerability maps to techniques involving privilege escalation and defense evasion, as exploitation could enable attackers to maintain persistent access to compromised systems. System administrators should also implement runtime monitoring to detect memory allocation anomalies and consider implementing kernel hardening measures such as stack canaries, address space layout randomization, and kernel module signing to further reduce the attack surface and potential impact of this vulnerability.