CVE-2021-3971Public exploit

Firmware modification via trusted NVRAM control variable

Published Apr 22, 2022 · Updated Aug 3, 2024

Security feature bypass in Lenovo Notebook BIOS allows local users with elevated privileges to disable SPI flash write protections. The SecureBackDoorPeim and SecureBackDoor drivers treat the cE! NVRAM variable as an instruction to skip programming BIOS Control and Protected Range registers during boot. Administrator access with firmware-environment privileges and a restart are required; SPI flash then becomes writable outside SMM, enabling persistent firmware modification.

CVSS severity6.7
Medium
EPSS probability1.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Security feature bypass in Lenovo Notebook BIOS allows local users with elevated privileges to disable SPI flash write protections. The SecureBackDoorPeim and SecureBackDoor drivers treat the cE! NVRAM variable as an instruction to skip programming BIOS Control and Protected Range registers during boot. Administrator access with firmware-environment privileges and a restart are required; SPI flash then becomes writable outside SMM, enabling persistent firmware modification.

The record

CVE
CVE-2021-3971
Published
Apr 22, 2022
Updated
Aug 3, 2024
Vendor
Lenovo
Product
Notebook BIOS
Classifications
CWE-489, T1542.001, T1562
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Apr 22, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=various

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Lenovo · Notebook BIOSversion=various

Published CVSS scores

4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
6.7Lenovo Group Ltd.CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-489Active Debug Code
T1542.001Pre-OS Boot: System Firmware
T1562Impair Defenses

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo