CVE-2023-27373

Firmware integrity compromise via unchecked EFI variable

Published Aug 7, 2023 · Updated Mar 7, 2025

Improper input validation in Insyde InsydeH2O kernels 5.0 through 5.5 allows local users to compromise firmware integrity via an EFI variable. The TSEG overlap check accepts attacker-controlled values from a runtime-accessible EFI variable when assigning a dynamic Base Address Register, allowing the resulting range to overlap System Management RAM. The attack requires low-privilege local access and permits unauthorized modification of protected memory and a service interruption.

CVSS severity6.4
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Insyde InsydeH2O kernels 5.0 through 5.5 allows local users to compromise firmware integrity via an EFI variable. The TSEG overlap check accepts attacker-controlled values from a runtime-accessible EFI variable when assigning a dynamic Base Address Register, allowing the resulting range to overlap System Management RAM. The attack requires low-privilege local access and permits unauthorized modification of protected memory and a service interruption.

The record

CVE
CVE-2023-27373
Published
Aug 7, 2023
Updated
Mar 7, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 7, 2023CVE publishedPublication date reported by the CVE source.
  2. Mar 7, 2025Record 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 privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
6.4Insyde SoftwareCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:H/A:L
5.5CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

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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