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Fencer Vulns
medium 4.0

CVE-2021-21781 json

An information disclosure vulnerability exists in the ARM SIGPAGE functionality of Linux Kernel v5.4.66 and v5.4.54.

published 2021-08-18 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-8953

cvss
4.0
version 3.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

An information disclosure vulnerability exists in the ARM SIGPAGE functionality of Linux Kernel v5.4.66 and v5.4.54. The latest version (5.11-rc4) seems to still be vulnerable. A userland application can read the contents of the sigpage, which can leak kernel memory contents. An attacker can read a process’s memory at a specific offset to trigger this vulnerability. This was fixed in kernel releases: 4.14.222 4.19.177 5.4.99 5.10.17 5.11

Patch / fix

  • linux Debian 14, Debian 13, Debian 12 5.10.19-1

debian advisories DEBIAN-CVE-2021-21781

  • linux Ubuntu 18.04 LTS 4.15.0-143.147
  • linux Ubuntu 20.04 LTS 5.4.0-71.79
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1102.109
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1043.45
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1041.44
  • linux-gke Ubuntu 20.04 LTS 5.4.0-1041.43
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1091.93
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1037.38

ubuntu advisories UBUNTU-CVE-2021-21781

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel RHEL 8 4.18.0-372.9.1.el8
  • perf RHEL 8 4.18.0-372.9.1.el8
  • bpftool RHEL 8 4.18.0-372.9.1.el8
  • kernel-core RHEL 8 4.18.0-372.9.1.el8
  • kernel-tools RHEL 8 4.18.0-372.9.1.el8
  • python3-perf RHEL 8 4.18.0-372.9.1.el8
  • kernel-modules RHEL 8 4.18.0-372.9.1.el8
  • kernel-zfcpdump RHEL 8 4.18.0-372.9.1.el8

red hat advisories RHSA-2022:1988

  • kernel-syms SLE Module for Development Tools 15 SP2 5.3.18-24.78.1
  • kernel-source SLE Module for Development Tools 15 SP2, SLE Module for Basesystem 15 SP2 5.3.18-24.78.1
  • kernel-default SLE Workstation Extension 15 SP2, SLE Module for Legacy 15 SP2, SLE Module for Basesystem 15 SP2 +3 more 5.3.18-24.78.1
  • kernel-preempt SLE Workstation Extension 15 SP2, SLE Module for Development Tools 15 SP2, SLE Module for Basesystem 15 SP2 5.3.18-24.78.1
  • kernel-obs-build SLE Module for Development Tools 15 SP2 5.3.18-24.78.1
  • kernel-default-base SLE Module for Basesystem 15 SP2, SLE Micro 5.0 5.3.18-24.78.1.9.36.1
  • kernel-64kb SLE Module for Basesystem 15 SP3 5.3.18-59.19.1
  • kernel-syms SLE Module for Development Tools 15 SP3 5.3.18-59.19.1

suse advisories SUSE-SU-2021:2756-1SUSE-SU-2021:2687-1SUSE-SU-2021:2678-1SUSE-SU-2021:2646-1SUSE-SU-2021:2645-1

  • dtb-aarch64 openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-64kb openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-syms openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-obs-qa openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-source openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-default openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-preempt openSUSE Leap 15.3 5.3.18-59.19.1
  • kernel-kvmsmall openSUSE Leap 15.3 5.3.18-59.19.1

opensuse advisories openSUSE-SU-2021:2687-1openSUSE-SU-2021:1142-1openSUSE-SU-2021:2645-1

  • kernel AlmaLinux 8 4.18.0-372.9.1.el8
  • perf AlmaLinux 8 4.18.0-372.9.1.el8
  • bpftool AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-core AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-tools AlmaLinux 8 4.18.0-372.9.1.el8
  • python3-perf AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-modules AlmaLinux 8 4.18.0-372.9.1.el8
  • kernel-debug-core AlmaLinux 8 4.18.0-372.9.1.el8

almalinux advisories ALSA-2022:1988

  • kernel Rocky Linux 8 4.18.0-372.9.1.el8

rocky linux advisories RLSA-2022:1988

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-2021-21781 updated cvss 4.0

kernel: arm: SIGPAGE information disclosure vulnerability

  • Red Hat Enterprise Linux 7 kernel-alt
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-372.9.1.el8, kernel 4.18.0-372.9.1.el8, bpftool 4.18.0-372.9.1.el8, kernel-core 4.18.0-372.9.1.el8, kernel-tools 4.18.0-372.9.1.el8, python3-perf 4.18.0-372.9.1.el8, +15 more Red Hat Enterprise Linux CRB (v. 8) kernel-debuginfo-common-x86_64 4.18.0-372.9.1.el8, kernel-debuginfo-common-aarch64 4.18.0-372.9.1.el8, kernel-debuginfo-common-ppc64le 4.18.0-372.9.1.el8
    fixed: vendor fix RHSA-2022:1988
  • 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 Red Hat Enterprise Linux 8 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +6 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +81 more
    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

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • talosintelligence.com https://talosintelligence.com/vulnerability_reports/TALOS-2021-1243 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.0 4.0 CVSS:3.0/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
NVD 3.1 3.3 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:P/I:N/A:N

Affected products

  • n/a Linux Kernel

Classification

Weakness
  • CWE-908 Use of Uninitialized Resource
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.