CVE-2021-3975: A use-after-free flaw was found in libvirt
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MEDIUM 6.5WATCHLISTUPGRADEMITIGATEMITIGATE
CVE-2021-3975 is a medium-severity flaw (CVSS 6.5) affecting libvirt, ubuntu linux, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.
A use-after-free flaw was found in libvirt. The qemuMonitorUnregister() function in qemuProcessHandleMonitorEOF is called using multiple threads without being adequately protected by a monitor lock. This flaw could be triggered by the virConnectGetAllDomainStats API when the guest is shutting down. An unprivileged client with a read-only connection could use this flaw to perform a denial of service attack by causing the libvirt daemon to crash.
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
canonical ubuntu linux MITIGATE
Affected: 21.10
Fixed in: no fixed release known
Safe to downgrade to: a release before 21.10
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
fedoraproject fedora MITIGATE
Affected: 35
Fixed in: no fixed release known
Safe to downgrade to: a release before 35
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
redhat enterprise linux MITIGATE
Affected: 8.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 8.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
redhat enterprise linux eus MITIGATE
Affected: 8.6
Fixed in: no fixed release known
Safe to downgrade to: a release before 8.6
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
redhat enterprise linux for ibm z systems MITIGATE
Affected: 8.0
Fixed in: no fixed release known
Safe to downgrade to: a release before 8.0
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Verify at the official sourceNVD · CVE Program · Report a problem with this page Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.
Quick answers
How do I fix CVE-2021-3975?
libvirt: upgrade to 7.1.0; ubuntu linux: mitigate or apply the listed mitigation; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-3975 being exploited?
CVE-2021-3975 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.
What does CVE-2021-3975 affect?
CVE-2021-3975 affects libvirt, ubuntu linux, fedora. Severity is medium (CVSS 6.5). A use-after-free flaw was found in libvirt. The qemuMonitorUnregister() function in qemuProcessHandleMonitorEOF is called using multiple threads without being adequately protected by a monitor lock. This flaw could be triggered by the virCo
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