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Fencer Vulns
high 7.1

CVE-2021-3501 json

A flaw was found in the Linux kernel in versions before 5.12.

published 2021-05-05 5 y ago modified 2026-08-05 3 mo ago also EUVD-2021-26821

cvss
7.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 31%
public exploits
0
none known

Summary

A flaw was found in the Linux kernel in versions before 5.12. The value of internal.ndata, in the KVM API, is mapped to an array index, which can be updated by a user process at anytime which could lead to an out-of-bounds write. The highest threat from this vulnerability is to data integrity and system availability.

Patch / fix

  • Linux kernel 5.10.32, 5.11.16
  • linux Debian 14, Debian 13, Debian 12 5.10.38-1

debian advisories DEBIAN-CVE-2021-3501

  • linux-oem-5.10 Ubuntu 20.04 LTS 5.10.0-1029.30

ubuntu advisories UBUNTU-CVE-2021-3501

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

  • redhat-virtualization-host rhev hypervisor 4.4 4.4.6-20210615.0.el8_4
  • redhat-virtualization-host-image-update rhev hypervisor 4.4 4.4.6-20210615.0.el8_4
  • kernel RHEL 8 4.18.0-305.3.1.el8_4
  • perf RHEL 8 4.18.0-305.3.1.el8_4
  • bpftool RHEL 8 4.18.0-305.3.1.el8_4
  • kernel-core RHEL 8 4.18.0-305.3.1.el8_4
  • kernel-tools RHEL 8 4.18.0-305.3.1.el8_4
  • python3-perf RHEL 8 4.18.0-305.3.1.el8_4

red hat advisories RHSA-2021:2522RHSA-2021:2168RHSA-2021:2169RHSA-2021:2165

  • kernel Rocky Linux 8 4.18.0-305.3.1.el8_4

rocky linux advisories RLSA-2021:2168

  • kernel CBL-Mariner 2.0 5.10.78.1-1

azure linux advisories AZL-6569

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

  • linux Arch Linux 5.11.16.arch1-1
  • linux-hardened Arch Linux 5.11.16.hardened1-1
  • linux-zen Arch Linux 5.11.16.zen1-1
  • linux-lts Arch Linux 5.10.32-1

arch linux advisories AVG-1851AVG-1852AVG-1853AVG-1854

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-2021-3501 updated cvss 7.8

kernel: userspace applications can misuse the KVM API to cause a write of 16 bytes at an offset up to 32 GB from vcpu->run

  • Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-305.3.1.el8_4, kernel-debuginfo-common-aarch64 4.18.0-305.3.1.el8_4, kernel-debuginfo-common-ppc64le 4.18.0-305.3.1.el8_4 Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-305.3.1.el8_4, kernel 4.18.0-305.3.1.el8_4, bpftool 4.18.0-305.3.1.el8_4, kpatch-patch-4_18_0-305 1-1.el8, kernel-core 4.18.0-305.3.1.el8_4, kernel-tools 4.18.0-305.3.1.el8_4, +16 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update as soon as possible.” RHSA-2021:2168
  • Red Hat Enterprise Linux Real Time (v. 8) kernel-rt 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-core 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-modules 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-debug-core 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-debug-modules 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-modules-extra 4.18.0-305.3.1.rt7.75.el8_4, +2 more Red Hat Enterprise Linux Real Time for NFV (v. 8) kernel-rt 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-kvm 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-core 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-modules 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-debug-kvm 4.18.0-305.3.1.rt7.75.el8_4, kernel-rt-debug-core 4.18.0-305.3.1.rt7.75.el8_4, +4 more
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update as soon as possible.” RHSA-2021:2169
  • Red Hat Virtualization 4 Hypervisor for RHEL 8 redhat-virtualization-host 4.4.6-20210615.0.el8_4, redhat-virtualization-host-image-update 4.4.6-20210615.0.el8_4
    fixed: vendor fix “Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update as soon as possible.” RHSA-2021:2522
  • Red Hat Enterprise Linux 5 kernel 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, kernel-alt, python-perf, +9 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more Red Hat RHEL 8-based RHEV-H for RHEV 4 (build requirements) redhat-release-virtualization-host 4.4.6-2.el8ev, redhat-virtualization-host-image-update-placeholder 4.4.6-2.el8ev
    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

0.38% chance of exploitation in the next 30 days, higher than 31% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.1 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H
NVD 2.0 3.6 AV:L/AC:L/Au:N/C:N/I:P/A:P

Affected products

  • Linux kernel

Classification

Weakness
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.