CVE-2026-20753

Privileged code execution via Ext2 descriptor-size overflow

Published May 12, 2026 · Updated May 12, 2026

Integer overflow in Intel Slim Bootloader UEFI firmware allows local users to execute code through a crafted Ext2 filesystem. Ext2fsOpen allocates its group-descriptor array after multiplying untrusted Ext2FsNumCylinder by the descriptor size without checking for UINTN overflow. High privileges, a crafted Ext2 filesystem, and a 32-bit build are required; successful exploitation runs code in the boot-firmware context.

CVSS severity8.7
High
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in Intel Slim Bootloader UEFI firmware allows local users to execute code through a crafted Ext2 filesystem. Ext2fsOpen allocates its group-descriptor array after multiplying untrusted Ext2FsNumCylinder by the descriptor size without checking for UINTN overflow. High privileges, a crafted Ext2 filesystem, and a 32-bit build are required; successful exploitation runs code in the boot-firmware context.

The record

CVE
CVE-2026-20753
Published
May 12, 2026
Updated
May 12, 2026
Vendor
Topcon Positioning Systems, Inc.
Product
Slim Bootloader
Classifications
CWE-190, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. May 12, 2026CVE publishedPublication date reported by the CVE source.
  2. May 12, 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?

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  1. Affected versionversion=See references

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

Topcon Positioning Systems, Inc. · Slim Bootloaderversion=See references

Published CVSS scores

8.7Intel CorporationCVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA: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.

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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 exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
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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