CVE-2021-3543

Host crash or privilege escalation via stale descriptor

Published Jun 1, 2021 · Updated Aug 3, 2024

Use-after-free in the Linux Kernel 4.18.0 Nitro Enclaves driver allows local users to crash the host or escalate privileges. The enclave-creation error path installs a file descriptor before copying the slot UID to userspace, then calls put_unused_fd after a failed copy and leaves userland holding a descriptor to a freed file object. Access normally requires a privileged local user in the ne group who manages enclave VMs; userfaultfd can trigger the bad cleanup without a race.

CVSS severity6.7
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the Linux Kernel 4.18.0 Nitro Enclaves driver allows local users to crash the host or escalate privileges. The enclave-creation error path installs a file descriptor before copying the slot UID to userspace, then calls put_unused_fd after a failed copy and leaves userland holding a descriptor to a freed file object. Access normally requires a privileged local user in the ne group who manages enclave VMs; userfaultfd can trigger the bad cleanup without a race.

The record

CVE
CVE-2021-3543
Published
Jun 1, 2021
Updated
Aug 3, 2024
Vendor
The Linux Kernel Organization
Product
Linux Kernel
Classifications
CWE-476, CWE-416, T1068
Attack vector
local
Privileges
admin

Timeline

How it unfolded

  1. Jun 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=kernel 4.18.0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesadmin

What is affected?

The Linux Kernel Organization · Linux Kernelversion=kernel 4.18.0

Published CVSS scores

7.2NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:C
6.7NIST NVDCVSS:3.1/AV:L/AC:L/PR:H/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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-476NULL Pointer Dereference
CWE-416Use After Free
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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