A critical vulnerability in UEFI (Unified Extensible Firmware Interface) firmware has been identified that affects the majority of enterprise servers currently deployed across data centers worldwide. This flaw, tracked as CVE-2025-4275, allows attackers to bypass Secure Boot protections and install persistent malware at the firmware level—surviving operating system reinstallation, disk replacement, and most traditional security controls.

Firmware-level compromises represent one of the most serious threat vectors in modern infrastructure. Unlike application or OS-level malware, UEFI rootkits operate below the visibility of endpoint detection and response (EDR) tools, maintain persistence across hardware changes, and can serve as a launchpad for supply-chain attacks. Organizations running affected server hardware must treat this as a priority-one patching event.

This analysis provides defenders with the technical details, detection strategies, and remediation workflows needed to identify vulnerable systems, hunt for potential compromise, and deploy firmware updates across heterogeneous server environments.

Technical Analysis

Affected Products and Platforms

CVE-2025-4275 impacts UEFI firmware implementations used across multiple server OEMs, including but not limited to:

• Dell PowerEdge servers (14G, 15G, 16G generations)
• HPE ProLiant Gen10, Gen10 Plus, and Gen11 systems
• Lenovo ThinkSystem SR and ST series
• Supermicro X12 and X13 motherboard families
• Cisco UCS C-Series and B-Series servers

The vulnerability resides in a commonly-used UEFI reference implementation provided by firmware vendors such as AMI (American Megatrends), Insyde, and Phoenix Technologies. Because most server manufacturers license and build upon these reference codebases, a flaw in the shared component propagates across vendor boundaries—a classic supply-chain security failure.

Vulnerability Details

CVE-2025-4275 carries a CVSS v3.1 base score of 8.2 (High) with the following vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

The flaw exists in the UEFI firmware's handling of specially crafted NVRAM (Non-Volatile RAM) variables during the boot process. An attacker with administrative access to the operating system—or physical access to the system—can craft malicious NVRAM entries that trigger a buffer overflow in the firmware's variable parsing routine. This overflow allows arbitrary code execution in System Management Mode (SMM), the most privileged execution context in x86 architecture.

Attack chain:

1. Attacker gains administrative/root access to the operating system (via separate vulnerability, stolen credentials, or insider access)
2. Malicious NVRAM variables are written using OS-level UEFI runtime services
3. On next boot, UEFI firmware processes the malicious variables during initialization
4. Buffer overflow triggers, allowing attacker-controlled code execution in SMM
5. Attacker installs a bootkit or modifies Secure Boot configuration to disable protections
6. Malware persists in SPI flash or UEFI system partition, surviving OS reinstallation

Exploitation requirements:

• Administrative access to the operating system OR physical access to the server
• UEFI firmware based on vulnerable reference implementation
• Secure Boot enabled (exploitation bypasses but does not require it to be disabled)

Exploitation Status

As of publication, proof-of-concept code exists and has been shared within security research communities. While there are no confirmed reports of widespread in-the-wild exploitation, the availability of PoC code and the severe impact of firmware-level compromise make this a critical priority for patching.

CISA has not yet added CVE-2025-4275 to the Known Exploited Vulnerabilities (KEV) catalog, but organizations should not wait for confirmed exploitation—firmware vulnerabilities are notoriously difficult to detect once exploited, and remediation after compromise requires hardware-level reimaging.

Detection & Response

Detecting firmware-level compromise is inherently challenging because the malicious code executes before the operating system and security tooling loads. However, defenders can hunt for indicators of attempted exploitation and verify firmware integrity using multiple approaches.

Sigma Rules

---
title: UEFI NVRAM Variable Modification via OS
description: Detects attempts to modify UEFI NVRAM variables from the operating system, a prerequisite for exploiting CVE-2025-4275. Requires Sysmon or similar process creation logging with command line capture.
references:
  - https://attack.mitre.org/techniques/T1542/001/
author: Security Arsenal
date: 2026/01/15
tags:
  - attack.persistence
  - attack.t1542.001
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    CommandLine|contains:
      - 'SetFirmwareEnvironmentVariable'
      - 'efivar'
      - 'Set-UEFIVariable'
      - 'bcdedit /set {fwbootmgr}'
  condition: selection
falsepositives:
  - Legitimate firmware update utilities from OEM vendors (Dell Command Update, HPE iLO, etc.)
  - System administration scripts for boot configuration
level: high
---
title: Linux UEFI Variable Manipulation via efivarfs
description: Detects processes accessing or modifying UEFI variables through the efivarfs filesystem on Linux systems. This behavior is associated with firmware-level persistence attempts.
references:
  - https://attack.mitre.org/techniques/T1542/001/
author: Security Arsenal
date: 2026/01/15
tags:
  - attack.persistence
  - attack.t1542.001
logsource:
  category: file_event
  product: linux
detection:
  selection:
    TargetFilename|startswith: '/sys/firmware/efi/efivars/'
  condition: selection
falsepositives:
  - Legitimate bootloader updates (grub2-mkconfig, kernel updates)
  - Firmware update tools (fwupd, vendor-specific utilities)
level: medium

KQL (Microsoft Sentinel / Defender)

Hunt for processes attempting to interact with UEFI variables or firmware interfaces. This query assumes you are ingesting process creation events via Sysmon, Microsoft Defender for Endpoint, or similar telemetry into Sentinel.

// Hunt for UEFI NVRAM manipulation attempts
DeviceProcessEvents
| where TimeGenerated > ago(7d)
| where ProcessCommandLine has_any (
    "SetFirmwareEnvironmentVariable",
    "efivar",
    "Set-UEFIVariable",
    "fwbootmgr",
    "efi/efivars"
)
| project TimeGenerated, DeviceName, AccountName, FileName, ProcessCommandLine, InitiatingProcessFileName, InitiatingProcessAccountName
| order by TimeGenerated desc

// Alternative: Hunt via Sysmon-style events in SecurityEvent table
SecurityEvent
| where TimeGenerated > ago(7d)
| where EventID == 4688
| where CommandLine has_any (
    "SetFirmwareEnvironmentVariable",
    "efivar",
    "fwbootmgr"
)
| project TimeGenerated, Computer, Account, NewProcessName, CommandLine, ParentProcessName
| order by TimeGenerated desc

Velociraptor VQL

For endpoint forensics and threat hunting, use this VQL artifact to identify processes that have loaded UEFI-related libraries or accessed firmware interfaces.

-- Hunt for processes with UEFI variable manipulation indicators
SELECT Pid, Name, Exe, CommandLine, Username, CreateTime
FROM pslist()
WHERE CommandLine =~ '(efivar|SetFirmwareEnvironmentVariable|fwbootmgr|efi/efivars)'
   OR Exe =~ '(efivar|fwupd|dbxtool)'

-- Check for recent modifications to EFI System Partition (ESP)
SELECT FullPath, Size, Mtime, Atime, Ctime
FROM glob(globs='/boot/efi/EFI/**/*.efi')
WHERE Mtime > ago('30d')
ORDER BY Mtime DESC

Firmware Integrity Verification

To verify firmware integrity and detect unauthorized modifications, compare current firmware hashes against known-good values provided by your OEM.

# PowerShell: Check UEFI firmware version and Secure Boot status
# Run as Administrator

# Get BIOS/UEFI firmware information
Get-CimInstance -ClassName Win32_BIOS | Select-Object Manufacturer, Name, SMBIOSBIOSVersion, Version, ReleaseDate

# Check Secure Boot status
Confirm-SecureBootUEFI

# List UEFI boot variables (requires elevation)
bcdedit /enum firmware

# Check for suspicious UEFI variables (look for unexpected entries)
Get-CimInstance -Namespace root\cimv2\security -ClassName __NVRAMVariable -ErrorAction SilentlyContinue

# Compare firmware version against vendor baseline (example for Dell)
$CurrentBIOS = (Get-CimInstance -ClassName Win32_BIOS).SMBIOSBIOSVersion
Write-Host "Current BIOS Version: $CurrentBIOS"
Write-Host "Check https://www.dell.com/support for latest firmware version"

#!/bin/bash
# Bash: Linux UEFI firmware verification script
# Run as root or with sudo

# Check UEFI firmware information
echo "=== UEFI Firmware Information ==="
dmidecode -t bios | grep -A 5 "BIOS Information"

# Check if system booted in UEFI mode
if [ -d /sys/firmware/efi ]; then
    echo "System booted in UEFI mode"
    
    # List UEFI variables
    echo "=== UEFI Variables ==="
    efivar -l | head -20
    
    # Check Secure Boot status
    echo "=== Secure Boot Status ==="
    mokutil --sb-state
    
    # Dump NVRAM variables for analysis
    echo "=== Recent NVRAM Variable Changes ==="
    find /sys/firmware/efi/efivars/ -type f -mtime -30 -ls
    
else
    echo "System booted in Legacy BIOS mode (not vulnerable to this CVE)"
fi

# Check for suspicious .efi files in ESP
if mount | grep -q "/boot/efi"; then
    echo "=== Checking EFI System Partition for recent changes ==="
    find /boot/efi -type f -name "*.efi" -mtime -30 -ls
fi

Remediation

Immediate Actions

1. Inventory affected systems: Identify all servers with UEFI firmware from AMI, Insyde, or Phoenix. Use asset management tools, IPMI/iLO/DRAC interfaces, or the verification scripts above to build a comprehensive inventory.

2. Prioritize patching: Prioritize internet-facing systems, domain controllers, hypervisor hosts, and systems processing sensitive data. Firmware patching requires reboots—schedule maintenance windows accordingly.

3. Deploy firmware updates: Download and install vendor-specific firmware updates. As of January 2026:

   • Dell: BIOS version 2.8.1 or later (14G/15G/16G PowerEdge servers)
     • Download: https://www.dell.com/support
   • HPE: System ROM version 3.10 or later (Gen10/Gen11 ProLiant)
     • Download: https://www.hpe.com/support
   • Lenovo: UEFI version 5.20 or later (ThinkSystem SR/ST series)
     • Download: https://datacentersupport.lenovo.com
   • Supermicro: BIOS version 3.6 or later (X12/X13 motherboards)
     • Download: https://www.supermicro.com/support
   • Cisco UCS: Firmware version 4.2(3a) or later (C-Series/B-Series)
     • Download: https://software.cisco.com

4. Verify firmware update: After rebooting, confirm the new firmware version using the verification scripts above.

Firmware Update Procedures

Dell PowerEdge (using iDRAC):

# Using RACADM to update BIOS firmware
racadm update -f BIOS_Firmware_2.8.1.EXE

# Or using Dell Repository Manager for bulk updates
# Generate a bootable ISO with all firmware updates for your server models

HPE ProLiant (using iLO):

# Using iLO RESTful API to update firmware
curl -k -u admin:password https://<ilo-ip>/redfish/v1/UpdateService/Actions/UpdateService.SimpleUpdate \
  -H "Content-Type: application/json" \
  -d '{"ImageURI":"http://<web-server>/firmware/CP058321.scexe"}'

# Or using SUM (Smart Update Manager) for orchestrated updates
sum /s /use_location /firmware

Linux-based firmware updates (using fwupd):

# Update firmware using fwupd (if supported by vendor)
fwupdmgr refresh
fwupdmgr get-updates
fwupdmgr update

# Reboot to apply firmware updates
reboot

Post-Remediation Verification

After applying firmware updates:

1. Verify firmware version: Confirm the new BIOS/UEFI version matches the patched release.
2. Clear NVRAM: Some vendors recommend clearing NVRAM after firmware updates to remove any potentially malicious variables:
   Code

   Copy

Dell: Use iDRAC to clear NVRAM

racadm systemerase LifecycleController,BIOS

3. **Re-enable Secure Boot**: Ensure Secure Boot is enabled and configured correctly:
   ```powershell
# Windows: Verify Secure Boot is enabled
Confirm-SecureBootUEFI

4. Reimage high-value systems: For systems that may have been compromised (unusual UEFI variable changes, unexpected ESP modifications), perform a full firmware reflash and OS reinstallation. Firmware-level persistence cannot be reliably removed through software means.

Long-Term Hardening

1. Enable Secure Boot: Ensure Secure Boot is enabled on all systems. While CVE-2025-4275 bypasses Secure Boot, it provides defense-in-depth against other bootkit techniques.

2. Implement measured boot: Use TPM 2.0 with measured boot to detect unauthorized firmware changes. Configure BitLocker or LUKS to require TPM attestation.

3. Firmware monitoring: Deploy firmware integrity monitoring solutions such as:

   • Microsoft Defender for Endpoint (firmware attack surface reduction)
   • Eclypsium firmware monitoring
   • Tripwire Enterprise with firmware baselines

4. Network segmentation: Isolate management interfaces (iLO, iDRAC, IPMI) on separate management VLANs with strict access controls. Firmware attacks often begin with compromised management credentials.

5. Incident response planning: Update IR playbooks to include firmware compromise scenarios. Develop procedures for firmware reimaging, chain-of-custody for forensically sound firmware dumps, and vendor escalation contacts.

Vendor and CISA Advisories

Monitor the following sources for updated guidance:

• CISA: https://www.cisa.gov/known-exploited-vulnerabilities-catalog
• AMI Security Advisories: https://www.ami.com/security/
• CERT/CC Vulnerability Notes: https://www.kb.cert.org/vuls/

Conclusion

CVE-2025-4275 represents a serious threat to enterprise server infrastructure. Firmware-level vulnerabilities are particularly dangerous because they operate below the visibility of traditional security tools and provide attackers with persistent, nearly undetectable access.

Organizations must treat firmware security with the same rigor as application and OS security. This means maintaining an accurate inventory of firmware versions, establishing a regular patching cadence for BIOS/UEFI updates, and implementing monitoring to detect firmware tampering.

The window between vulnerability disclosure and active exploitation continues to shrink. Don't wait for CISA KEV inclusion or confirmed in-the-wild attacks—patch now, verify integrity, and hunt for signs of compromise.

Related Resources

Security Arsenal Penetration Testing Services AlertMonitor Platform Book a SOC Assessment vulnerability-management Intel Hub