CVE-2025-7026: SMI Handler Privilege Escalation Vulnerability

CVE-2025-7026 Overview

CVE-2025-7026 is a firmware vulnerability in a Software System Management Interrupt (SMI) handler triggered by SwSmiInputValue 0xB2. A local attacker with high privileges can control the RBX register, which the CommandRcx0 function dereferences as an unchecked pointer. When the contents at RBX match expected signatures such as $DB$ or 2DB$, the handler performs arbitrary writes into System Management RAM (SMRAM). Successful exploitation elevates privileges into System Management Mode (SMM), the most privileged execution context on x86 platforms. The flaw enables persistent firmware compromise that survives operating system reinstalls. CERT/CC and Binarly have published advisories tracking affected Gigabyte firmware.

Critical Impact

Local privilege escalation into SMM enables arbitrary SMRAM writes, bypassing OS-level protections and establishing persistent, stealthy firmware implants.

Affected Products

• Gigabyte motherboard firmware referencing the vulnerable CommandRcx0 SMI handler
• UEFI firmware images exposing SwSmiInputValue 0xB2 with unchecked RBX pointer dereference
• Refer to Gigabyte Security Support Information for affected model lists

Discovery Timeline

• 2025-07-11 - CVE-2025-7026 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-7026

Vulnerability Analysis

The vulnerability resides in a Software SMI handler invoked through I/O port 0xB2 with SwSmiInputValue 0xB2. When the SMI fires, the CPU enters SMM and the firmware dispatches the CommandRcx0 function. The handler reads attacker-controlled values from the RBX register passed in from ring 0 without validating that RBX points to memory outside SMRAM. If the dereferenced buffer contains specific magic values such as $DB$ or 2DB$, the handler proceeds to perform writes using attacker-influenced pointers. Because SMM operates above the operating system and hypervisor, writes into SMRAM allow the attacker to modify SMM code, hook subsequent SMIs, and disable firmware-based protections including Secure Boot policies.

Root Cause

The root cause is missing pointer validation inside an SMM dispatcher. SMI handlers must verify that buffers supplied by non-SMM code reside entirely outside SMRAM, typically using SmmIsBufferOutsideSmmValid. The CommandRcx0 function omits this check, trusting the RBX register as supplied by the caller in ring 0.

Attack Vector

An attacker with administrator or kernel privileges loads a driver or uses an existing signed driver to write the trigger value to I/O port 0xB2, setting RBX to point at a crafted structure beginning with $DB$ or 2DB$. The follow-on arbitrary write inside SMM is then leveraged to overwrite SMRAM contents and install a persistent SMM implant. Full technical analysis is available in the Binarly Security Advisory BRLY-DVA-2025-008 and the CERT Vulnerability Advisory #746790.

Detection Methods for CVE-2025-7026

Indicators of Compromise

• Kernel-mode drivers issuing writes to I/O port 0xB2 from unexpected processes
• Memory regions containing the magic signatures $DB$ or 2DB$ adjacent to SMM communication buffers
• Unexpected modifications to SMRAM measurements reported by TPM PCR values or firmware attestation
• Presence of unsigned or unknown drivers loaded prior to SMI invocation

Detection Strategies

• Monitor for processes loading kernel drivers that perform direct hardware I/O, particularly writes to port 0xB2
• Compare firmware images and SMM modules against vendor-supplied known-good hashes after boot
• Use platform firmware runtime measurement and attestation to detect SMRAM tampering

Monitoring Recommendations

• Collect Windows kernel telemetry on HalDispatchTable and direct port I/O via privileged drivers
• Audit driver load events and flag any non-vendor drivers exercising SMM communication paths
• Track firmware version inventory across endpoints and alert on hosts running pre-patch builds

How to Mitigate CVE-2025-7026

Immediate Actions Required

• Inventory affected motherboards and identify systems running vulnerable Gigabyte firmware
• Apply firmware updates published on the Gigabyte Security Support Information page as soon as vendor releases are available for your model
• Restrict administrative and kernel-mode access to trusted personnel, since exploitation requires high privileges
• Enable HVCI and Microsoft Vulnerable Driver Blocklist to limit loading of drivers that expose direct I/O port access

Patch Information

Gigabyte coordinates firmware fixes through its security support portal. Consult the CERT Vulnerability Advisory #746790 and the Binarly Security Advisory BRLY-DVA-2025-008 for the list of affected platforms and corresponding firmware revisions that introduce the missing SMRAM buffer validation.

Workarounds

• Enforce Secure Boot and measured boot to detect post-exploitation firmware tampering
• Block loading of known vulnerable third-party drivers that grant ring 0 I/O port access
• Apply application allowlisting and least privilege to prevent attackers from reaching the local administrator context required to trigger the SMI

# Verify Microsoft Vulnerable Driver Blocklist is enabled (Windows)
reg query "HKLM\SYSTEM\CurrentControlSet\Control\CI\Config" /v VulnerableDriverBlocklistEnable

# Confirm HVCI / Memory Integrity status via PowerShell
Get-CimInstance -ClassName Win32_DeviceGuard -Namespace root\Microsoft\Windows\DeviceGuard |
  Select-Object SecurityServicesRunning, VirtualizationBasedSecurityStatus