CVE-2026-64018: Linux Kernel Buffer Overflow Vulnerability

CVE-2026-64018 Overview

CVE-2026-64018 is an out-of-bounds array access vulnerability in the Linux kernel's Microsoft Azure Network Adapter (MANA) driver. The flaw resides in the mana_hwc_rx_event_handler() function, where the rx_req_idx value is derived from sge->address located in DMA-coherent memory. In Confidential Virtual Machines using AMD SEV-SNP or Intel TDX, this memory region is shared unencrypted with the host. Hardware or a malicious hypervisor can modify Work Queue Entry (WQE) contents at any time. The driver performs no bounds check on rx_req_idx before indexing the reqs[] array, enabling out-of-bounds access.

Critical Impact
Attackers with control over the host or hypervisor can trigger out-of-bounds memory access inside Confidential VMs, breaking the confidentiality and integrity guarantees of SEV-SNP and TDX environments.

Affected Products

Linux kernel MANA (Microsoft Azure Network Adapter) driver
Confidential VMs running on AMD SEV-SNP
Confidential VMs running on Intel TDX

Discovery Timeline

2026-07-19 - CVE-2026-64018 published to NVD
2026-07-20 - Last updated in NVD database

Technical Details for CVE-2026-64018

Vulnerability Analysis

The vulnerability affects the MANA driver's hardware channel receive event handler. When processing an RX completion, mana_hwc_rx_event_handler() reads rx_req_idx from a scatter-gather element residing in DMA-coherent memory. The driver then uses this index directly to access entries in the reqs[] array without validating that the value stays within array bounds.

In standard virtualization, DMA-coherent memory is trusted because the guest owns it. Confidential Computing inverts this trust model. Memory shared for DMA is explicitly outside the encrypted region and remains accessible to the untrusted hypervisor or hardware components at any moment. An attacker controlling the host can rewrite WQE contents after validation and before use, producing a classic time-of-check to time-of-use scenario against unvalidated indices.

Root Cause

The root cause is missing input validation on data sourced from untrusted shared memory. The MANA driver treats DMA-coherent memory as trusted, matching legacy assumptions in kernel networking drivers. Confidential VM threat models require that any value read from shared memory be validated before use, especially when the value acts as an array index.

Attack Vector

Exploitation requires a malicious or compromised hypervisor, host, or hardware component with the ability to modify the guest's DMA-coherent memory. The attacker writes an arbitrary rx_req_idx value into the WQE structure. When the guest kernel handles the receive event, it uses the attacker-controlled index to read or write outside the bounds of reqs[], corrupting kernel memory or leaking sensitive data from the confidential guest.

Because no verified public exploit or proof-of-concept code is available, technical details for reproduction are limited to the upstream patch commits referenced by kernel maintainers. See the Kernel Git Commit 763a372 for the fix implementation.

Detection Methods for CVE-2026-64018

Indicators of Compromise

Unexpected kernel oops or panic messages referencing mana_hwc_rx_event_handler in dmesg output on Azure or MANA-attached guests.
Anomalous MANA driver behavior such as receive queue stalls, malformed WQE warnings, or memory corruption traces in kernel logs.
Confidential VM guests reporting integrity violations or unexpected memory access faults during network I/O.

Detection Strategies

Inventory Linux kernel versions across Confidential VM workloads and flag hosts running unpatched MANA driver code.
Monitor kernel crash telemetry for stack traces containing mana_hwc symbols, which may indicate exploitation attempts or accidental triggering.
Correlate guest kernel panics with host-side hypervisor events to identify potentially malicious interactions with confidential guests.

Monitoring Recommendations

Enable kernel audit logging and forward /var/log/kern.log and journalctl -k output to a centralized SIEM for retention and correlation.
Track patch compliance of Linux kernels running on Azure Confidential VMs against the fix commits published on git.kernel.org.
Alert on abnormal reboot rates or kernel version rollbacks in Confidential VM fleets that could indicate exploitation or evasion.

How to Mitigate CVE-2026-64018

Immediate Actions Required

Apply the upstream Linux kernel patches that add bounds validation to rx_req_idx in mana_hwc_rx_event_handler() across all Confidential VM guests.
Prioritize patching for Azure Confidential VM workloads using SEV-SNP or TDX, where the MANA driver is directly exposed.
Rebuild and redeploy custom kernels used in confidential workloads to include the fix commits referenced by kernel maintainers.

Patch Information

The fix adds an explicit bounds check on rx_req_idx before it is used to index reqs[]. Patches are available in the stable trees. See Kernel Git Commit 01f7f89, Kernel Git Commit 355e9f2, Kernel Git Commit 5ddc715, Kernel Git Commit 763a372, Kernel Git Commit b809d04, Kernel Git Commit fa627a5, and Kernel Git Commit ff1d5af.

Workarounds

No supported workaround exists that preserves MANA networking functionality; the driver must validate the index before use.
If patching is temporarily impossible, restrict Confidential VM deployments to hosts and hypervisor versions that are trusted and audited.
Where feasible, disable or unbind the MANA driver on affected guests until the patched kernel is deployed.

bash

# Verify running kernel version and MANA driver status
uname -r
lsmod | grep mana
dmesg | grep -i mana

# After patching, confirm the kernel includes the bounds check fix
rpm -q kernel   # RHEL/Oracle Linux
dpkg -l | grep linux-image   # Debian/Ubuntu