CVE-2021-26370
📋 TL;DR
This AMD firmware vulnerability allows attackers with local access to overwrite bootloader memory by exploiting improper address validation in SVC_LOAD_FW_IMAGE_BY_INSTANCE and SVC_LOAD_BINARY_BY_ATTRIB functions. This can lead to arbitrary code execution in the bootloader, potentially compromising system integrity and availability. Systems using affected AMD processors with vulnerable firmware versions are impacted.
💻 Affected Systems
- AMD Ryzen processors
- AMD EPYC processors
- AMD Athlon processors with Radeon Graphics
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise via bootloader manipulation, allowing persistent malware installation, bricking of hardware, or bypassing of security controls.
Likely Case
Local privilege escalation allowing attackers to gain higher privileges, install persistent backdoors, or disrupt system boot processes.
If Mitigated
Limited impact if proper access controls prevent local malicious code execution and firmware is updated.
🎯 Exploit Status
Requires local code execution capability; exploitation involves manipulating firmware loading functions.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: AGESA version 1.2.0.0 or later
Vendor Advisory: https://www.amd.com/en/corporate/product-security/bulletin/amd-sb-1021
Restart Required: Yes
Instructions:
1. Check motherboard/BIOS manufacturer for firmware updates. 2. Download appropriate firmware update from manufacturer. 3. Follow manufacturer's firmware update procedure. 4. Reboot system after update.
🔧 Temporary Workarounds
Restrict local code execution
allImplement strict access controls to prevent unauthorized local code execution.
Enable secure boot
allEnsure secure boot is enabled to verify bootloader integrity.
🧯 If You Can't Patch
- Implement strict least privilege access controls to limit local code execution capabilities
- Monitor for suspicious firmware/bootloader modification attempts and unauthorized local code execution
🔍 How to Verify
Check if Vulnerable:
Check BIOS/firmware version against manufacturer's documentation; vulnerable if AGESA version is older than 1.2.0.0Check Version:
System-specific: Check BIOS settings or use manufacturer's diagnostic tools (e.g., dmidecode on Linux, msinfo32 on Windows)Verify Fix Applied:
Verify BIOS/firmware version shows AGESA 1.2.0.0 or newer after update📡 Detection & Monitoring
Log Indicators:
- Unexpected firmware/bootloader modification attempts
- Suspicious local process execution with elevated privileges
Network Indicators:
- Not network exploitable; focus on local activity
SIEM Query:
Process execution events with suspicious parent-child relationships or attempts to access firmware interfaces