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Fencer Vulns
high 8.2

CVE-2021-4207 json

A flaw was found in the QXL display device emulation in QEMU.

published 2022-04-29 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-34065

cvss
8.2
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 34%
public exploits
0
none known

Summary

A flaw was found in the QXL display device emulation in QEMU. A double fetch of guest controlled values `cursor->header.width` and `cursor->header.height` can lead to the allocation of a small cursor object followed by a subsequent heap-based buffer overflow. A malicious privileged guest user could use this flaw to crash the QEMU process on the host or potentially execute arbitrary code within the context of the QEMU process.

Patch / fix

  • qemu qemu 7.0.0
  • qemu Debian 14, Debian 13, Debian 12 1:7.0+dfsg-1

debian advisories DEBIAN-CVE-2021-4207

  • qemu Ubuntu 18.04 LTS 1:2.11+dfsg-1ubuntu7.40
  • qemu Ubuntu 20.04 LTS 1:4.2-3ubuntu6.23
  • qemu Ubuntu 22.04 LTS 1:6.2+dfsg-2ubuntu6.2
  • qemu Ubuntu Pro 14.04 LTS 2.0.0+dfsg-2ubuntu1.47+esm6
  • qemu Ubuntu Pro 16.04 LTS 1:2.5+dfsg-5ubuntu10.51+esm4

ubuntu advisories UBUNTU-CVE-2021-4207

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

  • SLOF RHEL 8 20210217-1.module+el8.6.0+14480+c0a3aa0f
  • hivex RHEL 8 1.3.18-23.module+el8.6.0+14480+c0a3aa0f
  • netcf RHEL 8 0.2.8-12.module+el8.6.0+14480+c0a3aa0f
  • swtpm RHEL 8 0.7.0-1.20211109gitb79fd91.module+el8.6.0+14480+c0a3aa0f
  • libnbd RHEL 8 1.6.0-5.module+el8.6.0+14480+c0a3aa0f
  • nbdkit RHEL 8 1.24.0-4.module+el8.6.0+14480+c0a3aa0f
  • libtpms RHEL 8 0.9.1-0.20211126git1ff6fe1f43.module+el8.6.0+14480+c0a3aa0f
  • libvirt RHEL 8 8.0.0-5.2.module+el8.6.0+15256+3a0914fe

red hat advisories RHSA-2022:5821RHSA-2022:5002

  • qemu SLES for SAP 12 SP5, SLES 12 SP5 3.1.1.1-69.1
  • qemu SLES 12 SP2-BCL 2.6.2-41.76.1
  • qemu SLES for SAP 15 SP1, SLES 15 SP1-LTSS, SLES 15 SP1-BCL +4 more 3.1.1.1-150100.80.43.2
  • qemu SLES for SAP 15 SP2, SLES 15 SP2-LTSS, SLES 15 SP2-BCL +8 more 4.2.1-150200.69.1
  • qemu SLE Module for Server Applications 15 SP4, SLE Module for Basesystem 15 SP4, openSUSE Leap 15.4 6.2.0-150400.37.5.3
  • qemu-testsuite openSUSE Leap 15.4 6.2.0-150400.37.5.5
  • qemu-linux-user openSUSE Leap 15.4 6.2.0-150400.37.5.1
  • qemu SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.2 +2 more 5.2.0-150300.115.2

suse advisories SUSE-SU-2023:3015-1SUSE-SU-2023:2358-1SUSE-SU-2022:3768-1SUSE-SU-2022:3594-1SUSE-SU-2022:2260-1SUSE-SU-2022:2254-1

  • qemu openSUSE Tumbleweed 7.0.0-53.1

opensuse advisories openSUSE-SU-2024:12209-1

  • SLOF AlmaLinux 8 20210217-1.module_el8.6.0+2880+7d9e3703
  • hivex AlmaLinux 8 1.3.18-23.module_el8.6.0+2880+7d9e3703
  • netcf AlmaLinux 8 0.2.8-12.module_el8.6.0+2880+7d9e3703
  • swtpm AlmaLinux 8 0.7.0-1.20211109gitb79fd91.module_el8.6.0+2880+7d9e3703
  • libnbd AlmaLinux 8 1.6.0-5.module_el8.6.0+2880+7d9e3703
  • nbdkit AlmaLinux 8 1.24.0-4.module_el8.6.0+2880+7d9e3703
  • libtpms AlmaLinux 8 0.9.1-0.20211126git1ff6fe1f43.module_el8.6.0+2880+7d9e3703
  • libvirt AlmaLinux 8 8.0.0-5.2.module_el8.6.0+3071+a07c0ea5

almalinux advisories ALSA-2022:5821

  • hivex Rocky Linux 8 1.3.18-23.module+el8.7.0+1084+97b81f61
  • hivex Rocky Linux 8 1.3.18-23.module+el8.6.0+847+b490afdd
  • netcf Rocky Linux 8 0.2.8-12.module+el8.7.0+1084+97b81f61
  • netcf Rocky Linux 8 0.2.8-12.module+el8.4.0+534+4680a14e
  • netcf Rocky Linux 8 0.2.8-12.module+el8.6.0+847+b490afdd
  • swtpm Rocky Linux 8 0.7.0-1.20211109gitb79fd91.module+el8.6.0+847+b490afdd
  • libnbd Rocky Linux 8 1.6.0-5.module+el8.7.0+1084+97b81f61
  • libnbd Rocky Linux 8 1.6.0-5.module+el8.6.0+847+b490afdd

rocky linux advisories RLSA-2022:5821

  • qemu Azure Linux 3.0 6.2.0-18
  • qemu CBL-Mariner 2.0 6.2.0-13

azure linux advisories AZL-35155AZL-9619

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

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-2021-4207 updated cvss 7.5

QEMU: QXL: double fetch in qxl_cursor() can lead to heap buffer overflow

  • Red Hat Enterprise Linux 6 qemu-img, qemu-kvm, qemu-kvm-tools, qemu-guest-agent, qemu-guest-agent-win32 Red Hat Enterprise Linux 7 qemu-img, qemu-kvm, libcacard, qemu-img-ma, qemu-kvm-ma, qemu-kvm-tools, +5 more
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 Advanced Virtualization qemu-img, qemu-kvm, qemu-kiwi, qemu-kvm-core, qemu-kvm-tests, qemu-kvm-common, +9 more
    affected: no fix available, no fix planned “Will not fix”
  • Red Hat OpenStack Platform 10 (Newton) qemu-img-rhev, qemu-kvm-rhev, qemu-kvm-tools-rhev, qemu-kvm-common-rhev Red Hat OpenStack Platform 13 (Queens) qemu-img-rhev, qemu-kvm-rhev, qemu-kvm-tools-rhev, qemu-kvm-common-rhev
    affected: no fix planned “Out of support scope”
  • Red Hat Advanced Virtualization for RHEL 8.4.0.EUS netcf 0.2.8-12.module+el8.4.0+8855+a9e237a9, libnbd 1.6.0-5.module+el8.4.0+14155+dec4a5c7, nbdkit 1.24.0-1.module+el8.4.0+9341+96cf2672, hivex 1.3.18-21.module+el8.4.0+11609+2eba841a, nbdfuse 1.6.0-5.module+el8.4.0+14155+dec4a5c7, seabios 1.14.0-1.module+el8.4.0+8855+a9e237a9, +110 more
    fixed: vendor fix RHSA-2022:5002
  • Red Hat Enterprise Linux AppStream (v. 8) libnbd 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, netcf 0.2.8-12.module+el8.6.0+14480+c0a3aa0f, hivex 1.3.18-23.module+el8.6.0+14480+c0a3aa0f, nbdfuse 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, nbdkit 1.24.0-4.module+el8.6.0+14480+c0a3aa0f, SLOF 20210217-1.module+el8.6.0+14480+c0a3aa0f, +104 more Red Hat Enterprise Linux CRB (v. 8) libnbd 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, netcf 0.2.8-12.module+el8.6.0+14480+c0a3aa0f, hivex 1.3.18-23.module+el8.6.0+14480+c0a3aa0f, nbdfuse 1.6.0-5.module+el8.6.0+14480+c0a3aa0f, SLOF 20210217-1.module+el8.6.0+14480+c0a3aa0f, seabios 1.15.0-2.module+el8.6.0+14757+c25ee005, +38 more
    fixed: vendor fix RHSA-2022:5821
  • Red Hat Enterprise Linux 9 qemu-img, qemu-kvm, qemu-kvm-core, qemu-kvm-tools, qemu-pr-helper, qemu-kvm-common, +16 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

0.40% chance of exploitation in the next 30 days, higher than 34% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • starlabs.sg https://starlabs.sg/advisories/21-4207/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 8.2 CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H
NVD 2.0 4.6 AV:L/AC:L/Au:N/C:P/I:P/A:P

Affected products

  • n/a QEMU

Classification

Weakness
  • CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization
  • CWE-120 Buffer Copy without Checking Size of Input

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.