CVE-2026-23069: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-23069 Overview

A potential integer underflow vulnerability has been discovered in the Linux kernel's vsock/virtio transport layer. The flaw exists in the virtio_transport_get_credit() function where unsigned arithmetic operations can produce incorrect results when a peer shrinks its advertised buffer while data is in flight. This can lead to a large positive value being calculated, potentially allowing more data to be queued than the peer can handle.

Critical Impact

This vulnerability in the Linux kernel's vsock/virtio transport layer could allow buffer exhaustion or denial of service conditions when communication occurs between virtual machines and their host systems.

Affected Products

• Linux kernel with vsock/virtio transport support
• Virtualization environments using virtio sockets
• Systems running affected Linux kernel versions with vsock enabled

Discovery Timeline

• 2026-02-04 - CVE CVE-2026-23069 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-23069

Vulnerability Analysis

The vulnerability resides in the credit calculation mechanism within virtio_transport_get_credit(). The function uses unsigned arithmetic to determine the available credit for transmitting data over virtio sockets. The problematic calculation is:

ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);

This arithmetic operation is vulnerable to underflow when the peer reduces its advertised buffer allocation (peer_buf_alloc) while bytes are still in transit. Since all variables involved are unsigned integers, the subtraction can wrap around to produce an unexpectedly large positive value rather than a negative number, which would indicate no available credit.

Root Cause

The root cause is the use of unsigned integer arithmetic without proper bounds checking in credit calculation. When the peer dynamically adjusts its buffer allocation to a smaller value while transmission is ongoing, the subtraction operation can underflow. The lack of validation before performing the arithmetic operation means the function may return an incorrect credit value that far exceeds the actual available buffer space.

Attack Vector

The attack vector involves manipulating the timing of buffer allocation changes during active vsock communication. An attacker or misconfigured system could trigger this condition by:

1. Establishing a vsock connection between a guest VM and host
2. Initiating data transmission to populate the in-flight byte counter
3. Reducing the advertised peer buffer allocation while data remains in transit
4. The underflow produces a large credit value, potentially allowing excessive data queuing

The vulnerability manifests when the peer's buffer allocation changes dynamically during active communication. The fix involves reusing the existing virtio_transport_has_space() function which already handles this edge case correctly. For technical implementation details, see the kernel commit 02f9af192b98.

Detection Methods for CVE-2026-23069

Indicators of Compromise

• Unusual memory consumption patterns in vsock-related kernel subsystems
• Unexpected buffer overflow conditions in virtio socket communications
• Kernel warnings or errors related to vsock credit handling
• Performance degradation in guest-to-host communication channels

Detection Strategies

• Monitor kernel logs for vsock/virtio-related warnings or error messages
• Implement system call auditing for vsock operations in virtualized environments
• Deploy kernel-level monitoring for anomalous credit value calculations
• Review memory allocation patterns for virtio transport subsystems

Monitoring Recommendations

• Enable kernel tracing for vsock and virtio subsystems to capture abnormal behavior
• Configure alerting on kernel panic or oops events related to networking subsystems
• Monitor virtual machine resource usage for unexpected spikes during vsock communication
• Implement baseline monitoring for normal vsock traffic patterns to identify deviations

How to Mitigate CVE-2026-23069

Immediate Actions Required

• Update affected Linux kernel installations to patched versions
• Review virtualization configurations that rely on vsock communication
• Consider temporarily disabling vsock functionality if not critical to operations
• Apply vendor-provided kernel updates as soon as available

Patch Information

The Linux kernel maintainers have addressed this vulnerability by modifying virtio_transport_get_credit() to reuse the existing virtio_transport_has_space() function, which already handles the edge case of buffer allocation changes during transmission. Multiple patch commits have been released:

• Commit 02f9af192b98
• Commit 3ef3d52a1a98
• Commit d05bc313788f
• Commit ec0f1b3da806

Workarounds

• Disable vsock functionality if not required by setting CONFIG_VSOCKETS=n in kernel configuration
• Restrict vsock communication to trusted environments only
• Implement network segmentation to limit exposure of virtualized systems using vsock
• Monitor and limit the rate of buffer allocation changes in vsock communications

# Check if vsock module is loaded
lsmod | grep vsock

# Temporarily unload vsock modules if not needed
modprobe -r vmw_vsock_virtio_transport
modprobe -r vsock