CVE-2021-33834

Memory corruption via user-controlled IOCTL buffer length

Published Sep 8, 2023 · Updated Sep 26, 2024

Out-of-bounds write in Insyde H2OFFT 6.20.00 allows local users to corrupt memory or crash Windows via a crafted driver IOCTL. The iscflashx64.sys 3.9.3.0 handler for IOCTL 0x22229a mishandles a user-controlled NumberOfBytes value when allocating a buffer and copying memory. Local access to the installed Windows driver is required; exploitation discloses memory contents or interrupts the system with a crash.

CVSS severity4.9
Medium
EPSS probability0.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in Insyde H2OFFT 6.20.00 allows local users to corrupt memory or crash Windows via a crafted driver IOCTL. The iscflashx64.sys 3.9.3.0 handler for IOCTL 0x22229a mishandles a user-controlled NumberOfBytes value when allocating a buffer and copying memory. Local access to the installed Windows driver is required; exploitation discloses memory contents or interrupts the system with a crash.

The record

CVE
CVE-2021-33834
Published
Sep 8, 2023
Updated
Sep 26, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-787, T1499.004
Attack vector
local
Privileges
Unavailable

Timeline

How it unfolded

  1. Sep 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Sep 26, 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 privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.9Insyde SoftwareCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
7.1NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1499.004Endpoint Denial of Service: Application or System Exploitation

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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