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Fencer Vulns
medium 6.5

CVE-2021-4145 json

A NULL pointer dereference issue was found in the block mirror layer of QEMU in versions prior to 6.2.0.

published 2022-01-25 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-34014

cvss
6.5
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 32%
public exploits
0
none known

Summary

A NULL pointer dereference issue was found in the block mirror layer of QEMU in versions prior to 6.2.0. The `self` pointer is dereferenced in mirror_wait_on_conflicts() without ensuring that it's not NULL. A malicious unprivileged user within the guest could use this flaw to crash the QEMU process on the host when writing data reaches the threshold of mirroring node.

Patch / fix

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

debian advisories DEBIAN-CVE-2021-4145

  • 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-2022:1759

  • 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 CBL-Mariner 2.0 6.2.0-2

azure linux advisories AZL-8347

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-2021-4145 updated cvss 5.6

QEMU: NULL pointer dereference in mirror_wait_on_conflicts() in block/mirror.c

  • 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 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: workaround, no fix planned “Out of support scope”
  • 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 8 Advanced Virtualization qemu-img, qemu-kvm, qemu-kiwi, qemu-kvm-core, qemu-kvm-tests, qemu-kvm-common, +9 more 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

0.39% chance of exploitation in the next 30 days, higher than 32% of all scored CVEs (FIRST EPSS, 2026-11-08).

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 4.9 AV:L/AC:L/Au:N/C:N/I:N/A:C

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.