CVE-2026-31470: Linux Kernel Information Disclosure Flaw

CVE-2026-31470 Overview

A vulnerability has been identified in the Linux kernel's TDX (Trust Domain Extensions) guest driver affecting the handling of host-controlled quote buffer length validation. The flaw exists in the virt: tdx-guest component where the host-controlled value quote_buf->out_len is insufficiently validated before determining how many bytes of the quote are copied out to guest userspace.

In TDX environments with remote attestation, quotes are not considered private and can be forwarded to an attestation server. The vulnerability allows scenarios where the host specifies a response length larger than the guest's allocation, or otherwise races modifying the response while the guest consumes it. This can result in contents beyond the pages allocated for quote_buf (up to TSM_REPORT_OUTBLOB_MAX) being read out to guest userspace and potentially forwarded in attestation requests.

Critical Impact

This information disclosure vulnerability can cross container protection boundaries, not just local root, as some deployments implement per-container configs-tsm-report interfaces.

Affected Products

• Linux kernel with TDX guest virtualization support
• Linux kernel versions with vulnerable virt: tdx-guest driver
• TDX-enabled virtualization environments with remote attestation

Discovery Timeline

• 2026-04-22 - CVE CVE-2026-31470 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-31470

Vulnerability Analysis

This vulnerability represents an information disclosure issue caused by improper input validation of host-controlled buffer length values. The root cause lies in the trust boundary between the TDX guest and the host environment.

In TDX (Trust Domain Extensions) virtualization, the guest relies on the host to provide certain values, including the out_len field within the quote_buf structure. The vulnerable code path fails to properly validate that the host-specified out_len value does not exceed the guest's actual buffer allocation size. When the host provides a maliciously large value, the guest copies memory beyond its allocated buffer boundaries, potentially exposing sensitive kernel memory contents.

The vulnerability is particularly concerning in containerized environments where per-container configs-tsm-report interfaces are deployed. An exploit could allow information to leak across container boundaries, undermining container isolation guarantees.

Root Cause

The root cause is insufficient validation of the host-controlled quote_buf->out_len value in the TDX guest driver. The code path that copies quote data to guest userspace does not verify that the specified output length is within the bounds of the allocated quote_buf memory region. This creates a classic trust boundary violation where untrusted host input directly influences memory operations in the guest.

Additionally, the code is susceptible to a race condition where the host could modify the response length while the guest is consuming it, potentially causing inconsistent state and further memory safety issues.

Attack Vector

The attack vector involves a malicious or compromised host hypervisor manipulating the quote_buf->out_len value to specify a length larger than the guest's allocated buffer. When the guest processes an attestation quote request:

1. The guest allocates a buffer for the quote response with a specific size
2. The host fills the quote buffer and sets out_len to indicate the response size
3. The guest copies out_len bytes to userspace without verifying the value doesn't exceed allocation
4. Memory contents beyond the allocated pages (up to TSM_REPORT_OUTBLOB_MAX) are exposed

The leaked information could then be forwarded to an attestation server as part of normal attestation workflows, potentially exfiltrating sensitive data from kernel memory or adjacent container contexts.

Detection Methods for CVE-2026-31470

Indicators of Compromise

• Unusual memory access patterns in TDX guest virtualization contexts
• Attestation requests containing unexpectedly large quote data
• Kernel warnings or errors related to TDX guest buffer operations
• Anomalous data in attestation server logs that may indicate memory corruption

Detection Strategies

• Monitor kernel logs for TDX-related errors or warnings in the virt: tdx-guest driver
• Implement integrity checking on attestation quote sizes and contents
• Deploy kernel memory monitoring tools to detect out-of-bounds read operations
• Review attestation server logs for abnormally sized or malformed quote data

Monitoring Recommendations

• Enable verbose logging for TDX guest operations during security audits
• Implement anomaly detection for attestation request patterns and sizes
• Monitor container boundaries for unexpected data exposure in TDX environments
• Deploy SentinelOne Singularity Platform for real-time kernel-level threat detection and memory protection

How to Mitigate CVE-2026-31470

Immediate Actions Required

• Apply the latest Linux kernel patches that address this vulnerability
• Review and audit TDX guest deployments for potential exposure
• Implement additional validation layers for attestation data flows
• Consider temporarily disabling TDX remote attestation in highly sensitive environments until patched

Patch Information

The Linux kernel maintainers have released patches to address this vulnerability. The fix adds proper validation of the host-controlled quote_buf->out_len value to ensure it does not exceed the guest's buffer allocation. Multiple patch commits are available:

• Kernel Git Commit 02ca2d9
• Kernel Git Commit 6f3c879
• Kernel Git Commit a079a62
• Kernel Git Commit c3fd16c

System administrators should update to patched kernel versions as soon as possible.

Workarounds

• Restrict TDX guest attestation functionality to trusted environments only
• Implement application-level validation of attestation quote sizes before processing
• Use network segmentation to isolate attestation traffic from sensitive systems
• Deploy additional monitoring for TDX guest memory operations

# Check current kernel version for TDX support
uname -r

# Verify TDX guest driver status
lsmod | grep tdx

# Review kernel logs for TDX-related issues
dmesg | grep -i tdx