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Fencer Vulns
medium 6.3

CVE-2021-3631 json

A flaw was found in libvirt while it generates SELinux MCS category pairs for VMs' dynamic labels.

published 2022-03-02 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-26933

cvss
6.3
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 42%
public exploits
0
none known

Summary

A flaw was found in libvirt while it generates SELinux MCS category pairs for VMs' dynamic labels. This flaw allows one exploited guest to access files labeled for another guest, resulting in the breaking out of sVirt confinement. The highest threat from this vulnerability is to confidentiality and integrity.

Patch / fix

  • redhat libvirt 7.5.0
  • libvirt Debian 14, Debian 13, Debian 12 7.6.0-1

debian advisories DEBIAN-CVE-2021-3631

  • libvirt Ubuntu 18.04 LTS 4.0.0-1ubuntu8.21
  • libvirt Ubuntu 20.04 LTS 6.0.0-0ubuntu8.16
  • libvirt Ubuntu 22.04 LTS 7.6.0-0ubuntu3

ubuntu advisories UBUNTU-CVE-2021-3631

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 advanced virtualization 8.4 20200717-1.gite18ddad8.module+el8.4.0+8855+a9e237a9
  • hivex advanced virtualization 8.4 1.3.18-21.module+el8.4.0+11609+2eba841a
  • netcf advanced virtualization 8.4 0.2.8-12.module+el8.4.0+8855+a9e237a9
  • swtpm advanced virtualization 8.4 0.4.2-1.20201201git2df14e3.module+el8.4.0+9341+96cf2672
  • libnbd advanced virtualization 8.4 1.6.0-3.module+el8.4.0+9856+bbc47853
  • nbdkit advanced virtualization 8.4 1.24.0-1.module+el8.4.0+9341+96cf2672
  • libtpms advanced virtualization 8.4 0.7.4-4.20201106git2452a24dab.module+el8.4.0+10596+32ba7df3
  • libvirt advanced virtualization 8.4 7.0.0-14.4.module+el8.4.0+12413+d23780e6

red hat advisories RHSA-2021:3703RHSA-2021:3704RHSA-2021:4191

  • libvirt SLE Module for Server Applications 15 SP3, SLE Module for Basesystem 15 SP3 7.1.0-6.5.1
  • libvirt SLE Module for Server Applications 15 SP2, SLE Module for Basesystem 15 SP2, SLE Micro 5.0 6.0.0-13.16.2

suse advisories SUSE-SU-2021:2812-1SUSE-SU-2021:2471-1

  • libvirt openSUSE Tumbleweed 7.7.0-2.1
  • libvirt openSUSE Leap 15.3 7.1.0-6.5.1
  • libvirt openSUSE Leap 15.2 6.0.0-lp152.9.12.1

opensuse advisories openSUSE-SU-2024:11008-1openSUSE-SU-2021:2812-1openSUSE-SU-2021:1119-1

  • hivex AlmaLinux 8 1.3.18-21.module_el8.5.0+2608+72063365
  • netcf AlmaLinux 8 0.2.8-12.module_el8.5.0+2608+72063365
  • netcf AlmaLinux 8 0.2.8-12.module_el8.6.0+2880+7d9e3703
  • libnbd AlmaLinux 8 1.2.2-1.module_el8.5.0+2608+72063365
  • nbdkit AlmaLinux 8 1.16.2-4.module_el8.5.0+2608+72063365
  • libvirt AlmaLinux 8 6.0.0-37.module_el8.5.0+2608+72063365
  • nbdfuse AlmaLinux 8 1.2.2-1.module_el8.5.0+2608+72063365
  • seabios AlmaLinux 8 1.13.0-2.module_el8.5.0+2608+72063365

almalinux advisories ALSA-2021:4191

  • hivex Rocky Linux 8 1.3.18-21.module+el8.4.0+642+7e26f5e1
  • hivex Rocky Linux 8 1.3.18-21.module+el8.5.0+670+c4aa478c
  • 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
  • libnbd Rocky Linux 8 1.2.2-1.module+el8.4.0+534+4680a14e
  • nbdkit Rocky Linux 8 1.16.2-4.module+el8.4.0+534+4680a14e
  • libvirt Rocky Linux 8 6.0.0-37.module+el8.5.0+670+c4aa478c

rocky linux advisories RLSA-2021:4191

  • libvirt Alpine 3.24, Alpine 3.23, Alpine 3.22 +7 more 7.5.0-r0

alpine advisories ALPINE-CVE-2021-3631

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-2021-3631 updated cvss 3.0

libvirt: Insecure sVirt label generation

  • Red Hat Enterprise Linux 6 libvirt, libvirt-client, libvirt-python, libvirt-lock-sanlock Red Hat Enterprise Linux 7 libvirt, libvirt-nss, libvirt-libs, libvirt-admin, libvirt-client, libvirt-daemon, +24 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 Advanced Virtualization libvirt, libvirt-nss, libvirt-libs, libvirt-admin, libvirt-client, libvirt-daemon, +22 more
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Advanced Virtualization CodeReady Builder for RHEL 8.2.1 libnbd 1.2.2-1.module+el8.2.0+5644+32ac38d4, netcf 0.2.8-12.module+el8.2.0+4793+b09dd2fb, hivex 1.3.18-20.module+el8.2.0+5588+63a201c3, nbdfuse 1.2.2-1.module+el8.2.0+5644+32ac38d4, seabios 1.13.0-2.module+el8.2.1+7284+aa32a2c4, libiscsi 1.18.0-8.module+el8.2.0+4793+b09dd2fb, +45 more Red Hat Advanced Virtualization for RHEL 8.2.1 libnbd 1.2.2-1.module+el8.2.0+5644+32ac38d4, netcf 0.2.8-12.module+el8.2.0+4793+b09dd2fb, hivex 1.3.18-20.module+el8.2.0+5588+63a201c3, nbdfuse 1.2.2-1.module+el8.2.0+5644+32ac38d4, nbdkit 1.16.2-4.module+el8.2.1+6710+effcb1df, seabios 1.13.0-2.module+el8.2.1+7284+aa32a2c4, +96 more
    fixed: vendor fix RHSA-2021:3704
  • Red Hat Advanced Virtualization for RHEL 8.4.0.Z 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-2021:3703
  • Red Hat CodeReady Linux Builder (v. 8) libnbd 1.2.2-1.module+el8.3.0+7353+9de0a3cc, netcf 0.2.8-12.module+el8.1.0+4066+0f1aadab, nbdfuse 1.2.2-1.module+el8.3.0+7353+9de0a3cc, hivex 1.3.18-21.module+el8.5.0+10709+b3edb581, seabios 1.13.0-2.module+el8.3.0+7353+9de0a3cc, libiscsi 1.18.0-8.module+el8.1.0+4066+0f1aadab, +39 more Red Hat Enterprise Linux AppStream (v. 8) libnbd 1.2.2-1.module+el8.3.0+7353+9de0a3cc, netcf 0.2.8-12.module+el8.1.0+4066+0f1aadab, nbdfuse 1.2.2-1.module+el8.3.0+7353+9de0a3cc, nbdkit 1.16.2-4.module+el8.3.0+6922+fd575af8, hivex 1.3.18-21.module+el8.5.0+10709+b3edb581, seabios 1.13.0-2.module+el8.3.0+7353+9de0a3cc, +88 more
    fixed: vendor fix RHSA-2021:4191
  • Red Hat Enterprise Linux 9 libvirt, libvirt-nss, libvirt-libs, libvirt-client, libvirt-daemon, libvirt-ssh-proxy, +25 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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
23 mo ago

Exploit prediction

0.49% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • gitlab.com https://gitlab.com/libvirt/libvirt/-/issues/153 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.3 CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 3.3 AV:L/AC:M/Au:N/C:P/I:P/A:N

Affected products

  • n/a libvirt

Classification

Weakness
  • CWE-732 Incorrect Permission Assignment for Critical Resource

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.