Introduction
An attacker with local administrative access to an AMD Ryzen, Threadripper, or embedded system can use a firmware flaw to run code at the most privileged level of the processor. The flaw, CVE-2024-21947, comes from improper input validation and allows arbitrary code execution in System Management Mode (SMM). It affects millions of endpoints across consumer, enterprise, and industrial environments.
About AMD: AMD is one of the world's leading semiconductor companies, with a significant share of the global CPU and GPU markets. Its Ryzen and Threadripper product lines are widely used in desktops, laptops, and workstations, and its embedded processors run a range of industrial and IoT devices. Security issues in AMD firmware can have far-reaching consequences.
Technical information
CVE-2024-21947 is a vulnerability in the System Management Mode (SMM) implementation of multiple AMD processors. SMM is a special-purpose x86 CPU mode for low-level system management, and it runs at a higher privilege than the operating system or hypervisor.
The cause is improper input validation (CWE-20) in SMM handlers. A privileged attacker can pass crafted input to SMM interfaces, such as System Management Interrupts or shared memory buffers, and the firmware does not validate it properly. That lets the attacker overwrite arbitrary memory in the SMM context. Successful exploitation can give the attacker arbitrary code execution at the SMM level, which is extremely difficult to detect or remediate from the operating system.
Key technical points:
- The attack requires local access and high privileges (CVSS: AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:H/A:H)
- An attacker can exploit it with crafted SMI calls or by manipulating SMM communication buffers
- The flaw is in SMM code that handles external input without sufficient validation
- The root cause is missing bounds or format checks on input data that SMM handlers process
- No public code snippets or PoC were available at the time of writing
Patch information
AMD has released updated Platform Initialization (PI) firmware versions to fix CVE-2024-21947. AMD distributes these updates to OEMs, who integrate them into BIOS updates. For AMD Athlon 3000 Series Mobile Processors with Radeon Graphics (Dali), the fix is in firmware version Picasso-FP5 1.0.1.1, released March 7, 2024.
Action required:
- Contact your system OEM for the latest BIOS update that includes the fixed firmware version
- Make sure affected Dali processors run Picasso-FP5 1.0.1.1 or later
- Watch AMD and OEM advisories for updates covering other processor families
Patch source: AMD Product Security Bulletin AMD-SB-4012
Affected systems and versions
CVE-2024-21947 affects a wide range of AMD processors, including:
- AMD Ryzen desktop and mobile CPUs (multiple generations)
- AMD Threadripper workstation CPUs
- AMD embedded processors (R1000, R2000, V3000 series and others)
- AMD Athlon 3000 Series Mobile Processors with Radeon Graphics (Dali)
Specific patch version for Dali (Athlon 3000 Series Mobile):
- Vulnerable: Prior to Picasso-FP5 1.0.1.1
- Fixed: Picasso-FP5 1.0.1.1 (March 7, 2024) and later
AMD's official advisories list the other affected processor families. Check the relevant security bulletins, and confirm with your OEM which patches are available for your system and whether they apply.
Vendor security history
AMD has previously fixed multiple SMM and firmware vulnerabilities, including:
- Speculative execution side-channel flaws (Spectre, Meltdown variants)
- SMM callout vulnerabilities (see AMD-SB-7028)
- Multiple input validation and buffer handling issues in firmware
AMD runs a public bug bounty program and usually publishes detailed advisories and firmware updates. How quickly a patch is deployed depends on OEM integration and on how users apply updates. AMD has become more transparent and more engaged with the security community in recent years, but the complexity of the firmware supply chain is still a problem.
