CVE-2021-38160 Overview
CVE-2021-38160 is a buffer overflow vulnerability in the Linux kernel's virtio_console driver (drivers/char/virtio_console.c). The vulnerability exists in kernel versions before 5.13.4 and allows data corruption or loss when an untrusted device supplies a buf->len value that exceeds the allocated buffer size. This occurs due to insufficient validation of length values received from the virtual device, potentially enabling local attackers with low privileges to achieve code execution or cause system instability.
Critical Impact
A malicious or compromised virtual device can supply crafted buffer length values to trigger memory corruption, potentially leading to privilege escalation, data corruption, or denial of service in virtualized environments.
Affected Products
- Linux Kernel (versions prior to 5.13.4)
- NetApp HCI Bootstrap OS
- NetApp HCI Compute Node
- NetApp HCI Management Node
- NetApp SolidFire
- NetApp HCI Storage Node
- NetApp Element Software
- Debian Linux 9.0 and 10.0
- Red Hat Enterprise Linux 8.0
Discovery Timeline
- 2021-08-07 - CVE-2021-38160 published to NVD
- 2025-05-05 - Last updated in NVD database
Technical Details for CVE-2021-38160
Vulnerability Analysis
The vulnerability resides in the virtio_console driver, which handles virtual console devices in Linux virtualization environments. When retrieving buffers from the virtqueue via virtqueue_get_buf(), the driver directly assigns the length value provided by the device to the buffer's len field without validating that it does not exceed the buffer's actual allocated size. This missing bounds check creates a classic buffer overflow condition (CWE-120) where subsequent operations may read or write beyond the allocated buffer boundaries.
In virtualized environments where the host system or hypervisor may be untrusted or compromised, this vulnerability presents a significant risk. An attacker controlling the virtual device could manipulate the reported buffer length to cause out-of-bounds memory access, potentially corrupting kernel data structures or achieving arbitrary code execution within the guest kernel.
Root Cause
The root cause is the absence of length validation in the virtio_console driver when processing buffer lengths from the virtqueue. The driver trusts the len value returned by virtqueue_get_buf() without verifying it against the actual buffer size (buf->size). This violates the principle of never trusting data from external or potentially untrusted sources, especially in virtualization contexts where the guest kernel should not implicitly trust the host.
Attack Vector
The attack requires local access to a virtualized system where the attacker can control or influence the virtual device behavior. The attack vector is local with low attack complexity and requires low privileges. An attacker would need to:
- Gain control over the virtual device or host hypervisor
- Supply a malicious buffer length value through the virtqueue that exceeds the allocated buffer size
- Trigger buffer operations that use the corrupted length value
- Exploit the resulting memory corruption for privilege escalation or system compromise
buf = virtqueue_get_buf(port->in_vq, &len);
if (buf) {
- buf->len = len;
+ buf->len = min_t(size_t, len, buf->size);
buf->offset = 0;
port->stats.bytes_received += len;
}
Source: GitHub Linux Commit
The fix adds a bounds check using min_t() to ensure the assigned length never exceeds the buffer's actual size, preventing buffer overflow regardless of the value supplied by the device.
Detection Methods for CVE-2021-38160
Indicators of Compromise
- Unexpected kernel panics or system crashes in virtualized environments running affected kernel versions
- Anomalous memory access patterns or corruption in kernel memory regions associated with virtio_console operations
- Unusual behavior in virtual console devices or unexpected buffer handling errors in system logs
- Evidence of privilege escalation attempts originating from virtualized workloads
Detection Strategies
- Monitor kernel version across all virtualized systems to identify instances running kernels prior to 5.13.4
- Implement kernel-level monitoring for buffer overflow conditions in virtio subsystem drivers
- Deploy endpoint detection solutions capable of identifying anomalous kernel memory access patterns
- Review system logs for virtio_console-related errors or unexpected device behavior
Monitoring Recommendations
- Enable kernel auditing for virtio device operations in virtualized environments
- Configure alerting for kernel crashes or panics that may indicate exploitation attempts
- Monitor for unexpected changes in kernel memory regions used by virtio_console
- Implement continuous vulnerability scanning to track kernel versions across infrastructure
How to Mitigate CVE-2021-38160
Immediate Actions Required
- Update the Linux kernel to version 5.13.4 or later on all affected systems
- Apply vendor-specific patches from distribution maintainers (Debian, Red Hat, NetApp)
- Prioritize patching for systems in virtualized environments where host trust is a concern
- Review and restrict access to virtual device configurations in hypervisor settings
Patch Information
The vulnerability is addressed in Linux kernel version 5.13.4. The fix introduces bounds checking using min_t(size_t, len, buf->size) to ensure buffer lengths cannot exceed the allocated buffer size. The patch is available via the Linux Kernel ChangeLog 5.13.4 and the GitHub Linux Commit.
Distribution-specific patches are available from:
Workarounds
- Limit the use of virtio_console in high-security virtualized environments until patches can be applied
- Ensure strict access controls on hypervisor and virtual device configurations to prevent untrusted device manipulation
- Consider disabling virtio_console functionality if not required for operations
- Implement additional monitoring and runtime protection for kernel operations in virtualized systems
# Check current kernel version for vulnerability status
uname -r
# Verify if virtio_console module is loaded
lsmod | grep virtio_console
# Update kernel on Debian-based systems
apt-get update && apt-get upgrade linux-image-$(uname -r)
# Update kernel on Red Hat-based systems
yum update kernel
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
