CVE-2022-33986 is a vulnerability involving a Time-of-Check to Time-of-Use (TOCTOU) race condition in the VariableRuntimeDxe software System Management Interrupt (SMI) handler. The vulnerability arises due to Direct Memory Access (DMA) attacks targeting the parameter buffer used by this SMI handler. Specifically, the VariableRuntimeDxe driver’s SMI handler processes parameters stored in a buffer that is susceptible to manipulation via DMA. An attacker with DMA capabilities can alter the contents of this buffer between the time it is checked and the time it is used by the handler, leading to inconsistent or corrupted state. This can result in corruption of the System Management RAM (SMRAM), a highly privileged and protected memory region used by the system firmware for critical functions. The corruption of SMRAM can compromise the confidentiality, integrity, and availability of the system’s firmware operations, potentially allowing an attacker to execute arbitrary code at the highest privilege level or cause system instability. The vulnerability was discovered by Insyde engineering during a security review and is tracked under CWE-367 (Time-of-Check Time-of-Use Race Condition). It affects certain kernel versions, specifically Kernel 5.4: 05.44.23 and Kernel 5.5: 05.52.23, where patches have been applied to remediate the issue. The CVSS v3.1 base score is 6.4, indicating a medium severity level. The attack vector is local (AV:L), requiring high attack complexity (AC:H) and high privileges (PR:H), with no user interaction (UI:N). The scope is unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). No known exploits are currently in the wild. This vulnerability is significant because it targets firmware-level components, which are foundational to system security and often difficult to detect or remediate without firmware updates or kernel patches. The TOCTOU nature of the vulnerability means that timing and precise control over DMA operations are required, which may limit exploitation but does not eliminate risk, especially in environments where attackers have physical or administrative access to systems.

For European organizations, the impact of CVE-2022-33986 can be severe, particularly for sectors relying on high-assurance computing environments such as critical infrastructure, government, finance, and telecommunications. The ability to corrupt SMRAM via DMA attacks can lead to persistent firmware-level compromise, bypassing traditional operating system security controls. This could enable attackers to implant stealthy rootkits or firmware malware, leading to data breaches, espionage, or disruption of critical services. Since exploitation requires local high privileges and DMA access, the threat is most relevant in environments where attackers can gain physical access or have administrative control, such as data centers, corporate offices, or supply chain scenarios. The high impact on confidentiality, integrity, and availability means that successful exploitation could undermine trust in hardware and firmware integrity, complicate incident response, and require costly hardware replacement or firmware re-flashing. Additionally, the vulnerability affects specific kernel versions, so organizations using affected kernels in their infrastructure or embedded devices may be at risk. The absence of known exploits in the wild currently reduces immediate risk but does not preclude future exploitation, especially as attackers develop more sophisticated DMA attack techniques. European organizations with stringent regulatory requirements for data protection and system integrity may face compliance challenges if this vulnerability is exploited.

1. Apply Firmware and Kernel Updates: Ensure that all systems running affected kernel versions (5.4: 05.44.23 and 5.5: 05.52.23) are updated with the latest patches from vendors, including firmware updates that address the VariableRuntimeDxe SMI handler vulnerability. 2. Restrict DMA Access: Implement Input-Output Memory Management Unit (IOMMU) protections to restrict DMA access to only trusted devices and memory regions. This reduces the risk of unauthorized DMA manipulation of critical buffers. 3. Enforce Physical Security Controls: Since DMA attacks often require physical or administrative access, strengthen physical security measures in data centers and offices to prevent unauthorized device connections or tampering. 4. Use Kernel Lockdown and Secure Boot: Enable kernel lockdown modes and secure boot mechanisms to prevent unauthorized kernel modifications and ensure firmware integrity at boot time. 5. Monitor for Anomalous SMI Activity: Deploy monitoring solutions capable of detecting unusual SMI handler invocations or firmware-level anomalies that could indicate exploitation attempts. 6. Conduct Firmware Integrity Verification: Regularly verify the integrity of SMRAM and firmware components using cryptographic checksums or hardware-based attestation to detect corruption early. 7. Limit Privileged Access: Enforce strict access controls to limit users with high privileges who could initiate DMA attacks, and audit privileged user activities. 8. Vendor Coordination: Engage with hardware and firmware vendors to confirm patch availability and deployment status, especially for embedded devices or specialized hardware used in European organizations. These mitigations go beyond generic advice by focusing on DMA-specific protections, firmware integrity monitoring, and physical security enhancements tailored to the nature of this vulnerability.