CVE-2021-46988

Local kernel crash via unreleased userfaultfd page

Published Feb 28, 2024 · Updated May 11, 2026

Resource-release error in affected Linux kernel releases allows local users to crash the kernel through a crafted userfaultfd operation. In shmem_mfill_atomic_pte(), a failed copy leaves an allocated page pending, and a retry encountering exhausted tmpfs accounting returns without releasing it. Triggering the BUG_ON requires userfaultfd access, a failed copy, a retry after mmap_lock release, and concurrent tmpfs exhaustion; the resulting panic interrupts the host.

CVSS severity5.5
Medium
EPSS probability0.24%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Resource-release error in affected Linux kernel releases allows local users to crash the kernel through a crafted userfaultfd operation. In shmem_mfill_atomic_pte(), a failed copy leaves an allocated page pending, and a retry encountering exhausted tmpfs accounting returns without releasing it. Triggering the BUG_ON requires userfaultfd access, a failed copy, a retry after mmap_lock release, and concurrent tmpfs exhaustion; the resulting panic interrupts the host.

The record

CVE
CVE-2021-46988
Published
Feb 28, 2024
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-416, T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 28, 2024CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=4.11
  2. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f
  3. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <140cfd9980124aecb6c03ef2e69c72d0548744de
  4. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <2d59a0ed8b26b8f3638d8afc31f839e27759f1f6
  5. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <319116227e52d49eee671f0aa278bac89b3c1b69
  6. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <7ed9d238c7dbb1fdb63ad96a6184985151b0171c
  7. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <ad53127973034c63b5348715a1043d0e80ceb330
  8. Affected versionversion=cb658a453b9327ce96ce5222c24d162b5b65b564 <b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.11; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <07c9b834c97d0fa3402fb7f3f3b32df370a6ff1f; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <140cfd9980124aecb6c03ef2e69c72d0548744de; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <2d59a0ed8b26b8f3638d8afc31f839e27759f1f6; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <319116227e52d49eee671f0aa278bac89b3c1b69; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <7ed9d238c7dbb1fdb63ad96a6184985151b0171c; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <ad53127973034c63b5348715a1043d0e80ceb330; version=cb658a453b9327ce96ce5222c24d162b5b65b564 <b3f1731c6d7fbc1ebe3ed8eff6d6bec56d76ff43

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/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 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-416Use After Free
T1499Endpoint Denial of Service

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo