CVE-2021-26315
📋 TL;DR
This vulnerability in AMD's Platform Security Processor (PSP) boot ROM allows attackers to execute arbitrary code when encrypted firmware images are loaded, due to insufficient integrity verification after decryption. It affects systems with AMD processors that use the PSP for secure boot functionality. This is a hardware/firmware-level vulnerability that could compromise the system's security foundation.
💻 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 including bypass of secure boot, installation of persistent firmware-level malware, and potential theft of encryption keys and sensitive data.
Likely Case
Local privilege escalation allowing attackers to gain higher privileges on the system, potentially leading to full system control.
If Mitigated
Limited impact if systems are physically secured and have strict access controls, though firmware-level compromise remains possible.
🎯 Exploit Status
Exploitation requires physical access or administrative privileges to flash malicious firmware. No public exploit code is known.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Updated AGESA firmware versions (specific versions vary by motherboard manufacturer)
Vendor Advisory: https://www.amd.com/en/corporate/product-security/bulletin/amd-sb-1021
Restart Required: Yes
Instructions:
1. Check motherboard manufacturer's website for BIOS/UEFI updates. 2. Download latest BIOS/UEFI firmware containing patched AGESA. 3. Follow manufacturer's instructions to flash updated firmware. 4. Verify successful update in system BIOS/UEFI settings.
🔧 Temporary Workarounds
Physical Security Controls
allRestrict physical access to systems to prevent firmware flashing attacks
Secure Boot Enforcement
allEnable and enforce secure boot to prevent unauthorized firmware modifications
🧯 If You Can't Patch
- Implement strict physical security controls to prevent unauthorized access
- Monitor for unauthorized firmware modification attempts and maintain hardware integrity logs
🔍 How to Verify
Check if Vulnerable:
Check system BIOS/UEFI version against motherboard manufacturer's patched versions. Use 'wmic bios get smbiosbiosversion' on Windows or 'dmidecode -t bios' on Linux.Check Version:
Windows: wmic bios get smbiosbiosversion | Linux: sudo dmidecode -t bios | grep VersionVerify Fix Applied:
Verify BIOS/UEFI version matches or exceeds manufacturer's recommended patched version. Check that AGESA version includes fixes for CVE-2021-26315.📡 Detection & Monitoring
Log Indicators:
- BIOS/UEFI firmware modification events
- Unauthorized physical access logs
- Secure boot violation events
Network Indicators:
- Unusual outbound connections from firmware management interfaces
SIEM Query:
EventID=12 OR EventID=13 (System events for firmware changes) OR unauthorized physical access alerts