CVE-2025-20028 Overview
CVE-2025-20028 is a time-of-check time-of-use (TOCTOU) race condition in the WheaERST System Management Mode (SMM) module on certain Intel reference platforms. The flaw allows a local attacker holding privileged user access to escalate privileges by winning a race between input validation and use within SMM. Exploitation requires no user interaction but demands high attack complexity and specific environmental conditions. Successful exploitation can compromise confidentiality, integrity, and availability of the affected system at the firmware level.
Critical Impact
A successful race win against the SMM handler grants execution at System Management Mode privilege, the most privileged execution context on x86 platforms, beneath the operating system and hypervisor.
Affected Products
- Intel reference platforms shipping the WheaERST SMM module
- Firmware images derived from affected Intel reference BIOS
- Refer to Intel Security Advisory SA-01234 for the platform list
Discovery Timeline
- 2026-03-10 - CVE-2025-20028 published to NVD
- 2026-03-11 - Last updated in NVD database
Technical Details for CVE-2025-20028
Vulnerability Analysis
The vulnerability resides in the Windows Hardware Error Architecture Error Record Serialization Table (WheaERST) SMM handler. The handler validates attacker-controlled input, then accesses or operates on that input a second time without re-validating it. Between these two operations, an attacker running code on a second logical processor can modify the shared memory region used by the handler.
This is a textbook Time-of-Check Time-of-Use race condition, tracked under [CWE-367]. Because the handler executes in System Management Mode, a successful race results in code running with higher privileges than the kernel. The attacker bypasses operating system enforcement boundaries entirely.
Root Cause
The SMM handler reads a pointer or length value, validates it against expected bounds, and then dereferences the same value during processing. The validated copy is not pinned to SMRAM. An attacker modifies the original buffer after the check completes but before the use occurs, substituting a pointer that redirects writes into SMRAM or other protected regions.
Attack Vector
Exploitation requires local access and existing high privileges, typically ring 0 kernel execution. The attacker triggers a System Management Interrupt (SMI) that invokes the vulnerable WheaERST handler. A second thread concurrently overwrites the input structure to win the race window. Success rates depend on cache behavior, core count, and SMI dispatch timing, which accounts for the high attack complexity rating.
No verified public proof-of-concept code is available. Technical details are described in the Intel Security Advisory SA-01234.
Detection Methods for CVE-2025-20028
Indicators of Compromise
- Unexpected SMI rate spikes correlated with privileged process activity
- Firmware integrity measurement mismatches reported by TPM PCR values after boot
- Kernel drivers issuing rapid, repeated writes to memory regions referenced by SMI communication buffers
Detection Strategies
- Monitor for kernel-mode processes that map and repeatedly modify ACPI communication buffers used by SMM handlers
- Correlate elevated SMI counters with the loading of unsigned or newly observed kernel drivers
- Apply firmware attestation comparing measured boot values against a known-good baseline for the affected platform
Monitoring Recommendations
- Enable and forward Windows boot configuration and measured boot logs to a central data lake for analysis
- Track installation of low-level diagnostic or overclocking drivers that expose physical memory primitives
- Alert on processes invoking NtSystemDebugControl or similar privileged interfaces from non-administrative parent chains
How to Mitigate CVE-2025-20028
Immediate Actions Required
- Apply the BIOS or UEFI firmware update referenced in Intel Security Advisory SA-01234 once available from your system OEM
- Restrict administrative and kernel-driver-loading privileges to a minimal set of accounts
- Enable Hypervisor-protected Code Integrity (HVCI) and Secure Boot to raise the cost of obtaining the prerequisite privileged execution
Patch Information
Intel coordinates fixes with downstream OEMs. Affected customers must obtain updated firmware from their platform vendor that integrates Intel's corrected WheaERST SMM module. The fix copies attacker-controlled input into SMRAM before validation, eliminating the race window. Confirm the firmware version after update against the OEM advisory.
Workarounds
- Block loading of untrusted kernel drivers using Microsoft's vulnerable driver blocklist or equivalent allowlisting
- Disable physical memory access driver interfaces that are not required for production workloads
- Enforce platform attestation policies that quarantine systems running firmware versions known to contain the vulnerable module
# Verify firmware version on Windows to confirm patched BIOS is installed
wmic bios get smbiosbiosversion,manufacturer,releasedate
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
