CVE-2023-40238Public exploit

Firmware code execution via signed bitmap dimensions

Published Dec 7, 2023 · Updated Feb 25, 2026

Memory corruption in BmpDecoderDxe in Insyde InsydeH2O allows local users to execute firmware code via a crafted BMP logo. During RLE4/RLE8 decoding, signed PixelHeight and PixelWidth values determine BltBuffer positions without adequate bounds validation, enabling out-of-bounds writes. Exploitation requires privileged write access to the EFI System Partition; successful writes redirect DXE execution before the operating system boots and enable persistent firmware code execution.

CVSS severity6.1
Medium
EPSS probability1.86%
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 BmpDecoderDxe in Insyde InsydeH2O allows local users to execute firmware code via a crafted BMP logo. During RLE4/RLE8 decoding, signed PixelHeight and PixelWidth values determine BltBuffer positions without adequate bounds validation, enabling out-of-bounds writes. Exploitation requires privileged write access to the EFI System Partition; successful writes redirect DXE execution before the operating system boots and enable persistent firmware code execution.

The record

CVE
CVE-2023-40238
Published
Dec 7, 2023
Updated
Feb 25, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-122, CWE-312, T1542.001
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Dec 7, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 25, 2026Record 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

5.5CISA ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
5.5Insyde SoftwareCVSS:3.1/AV:P/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:L
6.1Insyde SoftwareCVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:C/C:H/I:N/A:L

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-122Heap-based Buffer Overflow
CWE-312Cleartext Storage of Sensitive Information
T1542.001Pre-OS Boot System Firmware

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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