CVE-2025-29950: System Management Mode (SMM) RCE Flaw

CVE-2025-29950 Overview

CVE-2025-29950 is an improper input validation vulnerability in AMD System Management Mode (SMM). A privileged local attacker can overwrite SMM stack memory and achieve arbitrary code execution at one of the most sensitive privilege levels on x86 platforms. SMM (Ring -2) runs beneath the operating system and hypervisor, so code executing in this context can bypass kernel protections, hypervisor isolation, and secure boot. AMD tracks the issue under advisories AMD Security Bulletin SB-3023 and AMD Security Bulletin SB-4013. The weakness is classified as [CWE-1274]: improper access control for volatile memory containing boot code.

Critical Impact
A privileged local attacker can execute arbitrary code within SMM, undermining firmware trust boundaries and persisting below the operating system.

Affected Products

AMD processors and platforms enumerated in AMD Security Bulletin SB-3023
AMD processors and platforms enumerated in AMD Security Bulletin SB-4013
Systems running vulnerable AGESA / platform firmware with the affected SMM handler

Discovery Timeline

2026-02-10 - CVE-2025-29950 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-29950

Vulnerability Analysis

System Management Mode is a highly privileged x86 execution mode used for firmware-level tasks such as power management, hardware error handling, and platform configuration. Code executes in SMRAM, an isolated region invisible to the operating system. When the CPU enters SMM through a System Management Interrupt (SMI), it saves state and executes handlers that operate above OS and hypervisor privilege levels.

CVE-2025-29950 stems from an SMM handler that fails to properly validate attacker-controlled input before writing to a stack buffer. A caller with sufficient privileges can craft SMI parameters that cause the handler to overwrite adjacent stack memory, including saved return addresses or function pointers, redirecting control flow inside SMRAM.

Successful exploitation yields arbitrary code execution in SMM. Consequences include tampering with firmware, installing pre-boot implants, disabling platform security features, and bypassing hypervisor and kernel isolation. See AMD advisories SB-3023 and SB-4013 for firmware version details.

Root Cause

The root cause is missing bounds and type validation on data consumed by an SMM handler. The handler trusts values passed from a lower privilege ring and writes them into a fixed-size stack region without enforcing length or structural constraints, aligning with [CWE-1274].

Attack Vector

The attack vector is local and requires high privileges, typically kernel-level access or ring 0 code on the target host. The attacker triggers a crafted SMI that invokes the vulnerable handler with malformed parameters. User interaction is not required. Attack complexity is high because the exploit must control specific memory layout and SMI entry state inside SMRAM.

// No verified public exploit code is available for CVE-2025-29950.
// Refer to AMD Security Bulletins SB-3023 and SB-4013 for technical details.

Detection Methods for CVE-2025-29950

Indicators of Compromise

Unexpected changes to firmware measurements or TPM PCR values across reboots on AMD platforms
Unsigned or unexpected SMI handlers detected by firmware integrity tooling such as CHIPSEC
Kernel drivers or privileged processes issuing atypical patterns of SMI triggers via outb to port 0xB2
BIOS or AGESA firmware versions predating the fixes listed in AMD SB-3023 and SB-4013

Detection Strategies

Inventory AMD platforms and correlate installed BIOS or AGESA versions against the fixed builds published by AMD and OEMs.
Monitor for loading of high-privilege kernel drivers that can issue SMIs, particularly signed vulnerable drivers historically abused for firmware access.
Use firmware assessment tools such as CHIPSEC and vendor attestation to validate SMRAM lock state and handler integrity.

Monitoring Recommendations

Enable measured boot and TPM-based remote attestation and alert on PCR drift for firmware components.
Collect endpoint telemetry on driver installation, NtLoadDriver activity, and access to \\.\PhysicalMemory or MSR interfaces.
Forward firmware and platform integrity events into a central data lake for cross-fleet baselining and anomaly analysis.

How to Mitigate CVE-2025-29950

Immediate Actions Required

Apply the BIOS or UEFI firmware update from the system OEM that incorporates the AGESA fixes referenced in AMD SB-3023 and SB-4013.
Restrict local administrator and kernel-level access to reduce the population of principals able to reach the vulnerable SMI handler.
Enforce driver signature policies and block known vulnerable drivers frequently abused for SMI-based attacks.

Patch Information

AMD published fixes and affected component lists in AMD Security Bulletin SB-3023 and AMD Security Bulletin SB-4013. Fixes are delivered through updated AGESA firmware, which OEMs package into BIOS or UEFI updates for specific platforms. Consult your server or workstation vendor for the exact firmware build addressing CVE-2025-29950 on your model.

Workarounds

No supported software workaround replaces the firmware fix; deploy the OEM BIOS update as the primary control.
Reduce the number of privileged accounts and enforce least privilege to limit who can trigger SMIs on affected hosts.
Enable hardware-based protections such as SMM Supervisor, SMRAM lock, and hypervisor-enforced code integrity where supported by the platform.

bash

# Example: verify installed BIOS version on Linux to compare against OEM fixed build
sudo dmidecode -s bios-version
sudo dmidecode -s bios-release-date

# Example: enumerate loaded kernel modules that may issue SMIs
lsmod | sort