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Fencer Vulns
high 7.8

CVE-2021-47461 json

userfaultfd: fix a race between writeprotect and exit_mmap()

published 2024-05-22 2 y ago modified 2026-08-05 3 mo ago also EUVD-2021-34466

cvss
7.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

userfaultfd: fix a race between writeprotect and exit_mmap()

A race is possible when a process exits, its VMAs are removed by exit_mmap() and at the same time userfaultfd_writeprotect() is called.

The race was detected by KASAN on a development kernel, but it appears to be possible on vanilla kernels as well.

Use mmget_not_zero() to prevent the race as done in other userfaultfd operations.

Patch / fix

  • Linux Linux 5.10.76, 5.14.15, 5.15
  • linux Debian 14, Debian 13, Debian 12 5.14.16-1

debian advisories DEBIAN-CVE-2021-47461

  • kernel-rt RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-kvm RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-core RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-modules RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-debug-kvm RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-debug-core RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-debug-modules RHEL 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel-rt-modules-extra RHEL 8 4.18.0-553.16.1.rt7.357.el8_10

red hat advisories RHSA-2024:10262RHSA-2024:5102RHSA-2024:5101RHSA-2024:6297

  • dtb-aarch64 openSUSE Leap 15.5 5.14.21-150500.55.68.1
  • kernel-64kb SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.68.1
  • kernel-syms SLE Module for Development Tools 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.68.1
  • kernel-obs-qa openSUSE Leap 15.5 5.14.21-150500.55.68.1
  • kernel-source SLE Module for Development Tools 15 SP5, SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.68.1
  • kernel-default SLE Workstation Extension 15 SP5, SLE Module for Legacy 15 SP5, SLE Module for Basesystem 15 SP5 +4 more 5.14.21-150500.55.68.1
  • kernel-kvmsmall openSUSE Leap 15.5 5.14.21-150500.55.68.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.68.1

suse advisories SUSE-SU-2024:2190-1SUSE-SU-2024:2189-1SUSE-SU-2024:2019-1SUSE-SU-2024:2011-1SUSE-SU-2024:2008-1

  • kernel AlmaLinux 8 4.18.0-553.16.1.el8_10
  • perf AlmaLinux 8 4.18.0-553.16.1.el8_10
  • bpftool AlmaLinux 8 4.18.0-553.16.1.el8_10
  • kernel-core AlmaLinux 8 4.18.0-553.16.1.el8_10
  • kernel-tools AlmaLinux 8 4.18.0-553.16.1.el8_10
  • python3-perf AlmaLinux 8 4.18.0-553.16.1.el8_10
  • kernel-modules AlmaLinux 8 4.18.0-553.16.1.el8_10
  • kernel-zfcpdump AlmaLinux 8 4.18.0-553.16.1.el8_10

almalinux advisories ALSA-2024:5101ALSA-2024:5102

  • kernel Rocky Linux 8 4.18.0-553.16.1.el8_10.cloud.0.1
  • kernel-rt Rocky Linux 8 4.18.0-553.16.1.rt7.357.el8_10
  • kernel Rocky Linux 8 4.18.0-553.16.1.el8_10

rocky linux advisories RXSA-2024:5101RLSA-2024:5102RLSA-2024:5101

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-47461 updated cvss 7.0

kernel: userfaultfd: fix a race between writeprotect and exit_mmap()

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
    affected: no fix planned “Out of support scope”
  • Red Hat CodeReady Linux Builder EUS (v.8.8) kernel-debuginfo-common-x86_64 4.18.0-477.81.1.el8_8, kernel-debuginfo-common-aarch64 4.18.0-477.81.1.el8_8, kernel-debuginfo-common-ppc64le 4.18.0-477.81.1.el8_8
    fixed: vendor fix RHSA-2024:10262
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-553.16.1.el8_10, kernel 4.18.0-553.16.1.el8_10, bpftool 4.18.0-553.16.1.el8_10, kernel-core 4.18.0-553.16.1.el8_10, kernel-tools 4.18.0-553.16.1.el8_10, python3-perf 4.18.0-553.16.1.el8_10, +15 more
    fixed: vendor fix RHSA-2024:5101
  • Red Hat Enterprise Linux BaseOS AUS (v.8.6) perf 4.18.0-372.121.1.el8_6, kernel 4.18.0-372.121.1.el8_6, bpftool 4.18.0-372.121.1.el8_6, kernel-core 4.18.0-372.121.1.el8_6, kernel-tools 4.18.0-372.121.1.el8_6, python3-perf 4.18.0-372.121.1.el8_6, +8 more Red Hat Enterprise Linux BaseOS E4S (v.8.6) perf 4.18.0-372.121.1.el8_6, kernel 4.18.0-372.121.1.el8_6, bpftool 4.18.0-372.121.1.el8_6, kernel-core 4.18.0-372.121.1.el8_6, kernel-tools 4.18.0-372.121.1.el8_6, python3-perf 4.18.0-372.121.1.el8_6, +15 more
    fixed: vendor fix RHSA-2024:6297
  • Red Hat Enterprise Linux BaseOS EUS (v.8.8) perf 4.18.0-477.81.1.el8_8, kernel 4.18.0-477.81.1.el8_8, bpftool 4.18.0-477.81.1.el8_8, kernel-core 4.18.0-477.81.1.el8_8, kernel-tools 4.18.0-477.81.1.el8_8, python3-perf 4.18.0-477.81.1.el8_8, +15 more
    fixed: vendor fix RHSA-2024:10262
  • Red Hat Enterprise Linux BaseOS TUS (v.8.6) perf 4.18.0-372.121.1.el8_6, kernel 4.18.0-372.121.1.el8_6, bpftool 4.18.0-372.121.1.el8_6, kernel-core 4.18.0-372.121.1.el8_6, kernel-tools 4.18.0-372.121.1.el8_6, python3-perf 4.18.0-372.121.1.el8_6, +8 more
    fixed: vendor fix RHSA-2024:6297
  • Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-553.16.1.el8_10, kernel-debuginfo-common-aarch64 4.18.0-553.16.1.el8_10, kernel-debuginfo-common-ppc64le 4.18.0-553.16.1.el8_10
    fixed: vendor fix RHSA-2024:5101
  • Red Hat Enterprise Linux NFV (v. 8) kernel-rt 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-kvm 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-core 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-modules 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-debug-kvm 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-debug-core 4.18.0-553.16.1.rt7.357.el8_10, +4 more Red Hat Enterprise Linux RT (v. 8) kernel-rt 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-core 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-modules 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-debug-core 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-debug-modules 4.18.0-553.16.1.rt7.357.el8_10, kernel-rt-modules-extra 4.18.0-553.16.1.rt7.357.el8_10, +2 more
    fixed: vendor fix RHSA-2024:5102
show 1 more
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux BaseOS AUS (v.8.6) kernel-doc 4.18.0-372.121.1.el8_6 Red Hat Enterprise Linux BaseOS E4S (v.8.6) kernel-doc 4.18.0-372.121.1.el8_6 Red Hat Enterprise Linux BaseOS TUS (v.8.6) kernel-doc 4.18.0-372.121.1.el8_6
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 4.7 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Linux Linux

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.