CVE-2021-33137

Local privilege escalation via unchecked USB endpoint index

Published Feb 9, 2022 · Updated May 5, 2025

An out-of-bounds write in Intel Kernelflinger's USB device-mode code allows local users to escalate privileges through endpoint metadata. DwcXdciEpClearStall derives a physical endpoint number and uses it to access EpHandles without first enforcing the 32-endpoint limit. Authenticated local access and an out-of-range endpoint value are required; successful exploitation corrupts bootloader memory and grants elevated privileges.

CVSS severity7.8
High
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

An out-of-bounds write in Intel Kernelflinger's USB device-mode code allows local users to escalate privileges through endpoint metadata. DwcXdciEpClearStall derives a physical endpoint number and uses it to access EpHandles without first enforcing the 32-endpoint limit. Authenticated local access and an out-of-range endpoint value are required; successful exploitation corrupts bootloader memory and grants elevated privileges.

The record

CVE
CVE-2021-33137
Published
Feb 9, 2022
Updated
May 5, 2025
Vendor
Intel Corporation
Product
Kernelflinger
Classifications
CWE-787, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 9, 2022CVE publishedPublication date reported by the CVE source.
  2. May 5, 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?

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  1. Affected versionversion=See references

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Intel Corporation · Kernelflingerversion=See references

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P
7.8Intel CorporationCVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
7.8CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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.

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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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
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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