CVE-2021-26943Public exploit

SMM code execution via unchecked error-path write

Published Mar 31, 2021 · Updated Aug 3, 2024

Memory corruption in ASUS UX360CA BIOS 303 and earlier allows local users with ring 0 privileges to execute arbitrary code in SMM. The UsbRt, SdioSmm, and NvmeSmm SMI handlers read a caller-controlled physical address and still write one byte through that pointer after validation fails, including into SMRAM. Kernel-level access and the ability to issue an SMI are required; successful exploitation bypasses kernel and hypervisor protections and enables SPI-flash modification for firmware persistence.

CVSS severity8.2
High
EPSS probability0.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory corruption in ASUS UX360CA BIOS 303 and earlier allows local users with ring 0 privileges to execute arbitrary code in SMM. The UsbRt, SdioSmm, and NvmeSmm SMI handlers read a caller-controlled physical address and still write one byte through that pointer after validation fails, including into SMRAM. Kernel-level access and the ability to issue an SMI are required; successful exploitation bypasses kernel and hypervisor protections and enables SPI-flash modification for firmware persistence.

The record

CVE
CVE-2021-26943
Published
Mar 31, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1542.001, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Mar 31, 2021CVE 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

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.2NIST NVDCVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
7.2NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:C

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

T1542.001Pre-OS Boot System Firmware
T1068Exploitation for Privilege Escalation

Public exploit references

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

Technologies

Your stack

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Your stack

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