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Fencer Vulns
medium 6.5

CVE-2021-20196 json

A NULL pointer dereference flaw was found in the floppy disk emulator of QEMU.

published 2021-05-26 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-7642

cvss
6.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

A NULL pointer dereference flaw was found in the floppy disk emulator of QEMU. This issue occurs while processing read/write ioport commands if the selected floppy drive is not initialized with a block device. This flaw allows a privileged guest user to crash the QEMU process on the host, resulting in a denial of service. The highest threat from this vulnerability is to system availability.

Patch / fix

  • qemu Debian 14, Debian 13, Debian 12 1:6.2+dfsg-1

debian advisories DEBIAN-CVE-2021-20196

  • qemu Ubuntu 18.04 LTS 1:2.11+dfsg-1ubuntu7.39
  • qemu Ubuntu 20.04 LTS 1:4.2-3ubuntu6.21
  • qemu Ubuntu 22.04 LTS 1:6.2+dfsg-2ubuntu5
  • 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-2021-20196

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.module+el8.6.0+14480+c0a3aa0f

red hat advisories RHSA-2022:1759RHSA-2022:0397RHSA-2022:0325

  • qemu SLES for SAP 12 SP5, SLES 12 SP5 3.1.1.1-63.4
  • qemu SLE Real Time 15 SP2, SLE Micro 5.0 4.2.1-11.34.2
  • qemu SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3, SLE Micro 5.1 5.2.0-150300.109.2

suse advisories SUSE-SU-2022:1151-1SUSE-SU-2022:0210-2SUSE-SU-2022:0210-1SUSE-SU-2022:0177-1

  • qemu openSUSE Leap 15.3 4.2.1-11.34.2
  • qemu openSUSE Leap 15.3 5.2.0-150300.109.2
  • qemu-testsuite openSUSE Leap 15.3 5.2.0-150300.109.4
  • qemu-linux-user openSUSE Leap 15.3 5.2.0-150300.109.2

opensuse advisories openSUSE-SU-2022:0210-1openSUSE-SU-2022:0177-1

  • 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.module_el8.6.0+2880+7d9e3703

almalinux advisories ALSA-2022:1759

  • 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-2022:1759

  • qemu Alpine 3.15 6.1.1-r0

alpine advisories ALPINE-CVE-2021-20196

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

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-2021-20196 updated cvss 3.2

QEMU: block: fdc: null pointer dereference may lead to guest crash

  • Red Hat Enterprise Linux 5 kvm, xen Red Hat Enterprise Linux 6 qemu-img, qemu-kvm, qemu-kvm-tools, qemu-guest-agent, qemu-guest-agent-win32
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 qemu-img, qemu-kvm, libcacard, qemu-kvm-rhev, qemu-kvm-tools, libcacard-tools, +2 more 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 “Fix deferred”
  • 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 “Will not fix”
  • Red Hat Advanced Virtualization for RHEL 8.4.0.EUS libnbd 1.6.0-3.module+el8.4.0+9856+bbc47853, netcf 0.2.8-12.module+el8.4.0+8855+a9e237a9, nbdfuse 1.6.0-3.module+el8.4.0+9856+bbc47853, nbdkit 1.24.0-1.module+el8.4.0+9341+96cf2672, hivex 1.3.18-21.module+el8.4.0+11609+2eba841a, seabios 1.14.0-1.module+el8.4.0+8855+a9e237a9, +110 more
    fixed: vendor fix RHSA-2022:0325
  • Red Hat Advanced Virtualization for RHEL 8.5.0.Z netcf 0.2.8-12.module+el8.4.0+8855+a9e237a9, libnbd 1.6.0-4.module+el8.5.0+11638+3d8f9850, hivex 1.3.18-22.module+el8.5.0+12087+2208d04c, libvirt 7.6.0-6.module+el8.5.0+13051+7ddbe958, nbdfuse 1.6.0-4.module+el8.5.0+11638+3d8f9850, nbdkit 1.24.0-3.module+el8.5.0+13900+a08c0464, +110 more
    fixed: vendor fix RHSA-2022:0397
  • 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, libvirt 8.0.0-5.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, +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, libvirt 8.0.0-5.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, +38 more
    fixed: vendor fix RHSA-2022:1759
  • Red Hat Enterprise Linux 7 qemu-img-ma, qemu-kvm-ma, qemu-kvm-tools-ma, qemu-kvm-common-ma
    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

0.48% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • bugs.launchpad.net https://bugs.launchpad.net/qemu/+bug/1912780 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.5 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H
NVD 2.0 2.1 AV:L/AC:L/Au:N/C:N/I:N/A:P

Affected products

  • n/a qemu

Classification

Weakness

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.