CVE-2021-43039: An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5

This week

MEDIUM 6.5REMOTEUPGRADE

CVE-2021-43039 is a medium-severity flaw (CVSS 6.5) affecting unitrends backup. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. The Samba file sharing service allowed anonymous read/write access.

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.3% (top 31%)
CISA exploited list	No
Published	2021-12-06
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: kaseya

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-12-06 04:15 UTCPublished CVE record published
2026-06-17 04:10 UTCUpdated Record last modified

kaseya unitrends backup UPGRADE

Affected: >= 10.0 and < 10.5.5

Fixed in: 10.5.5

Safe to downgrade to: a release before 10.0

1. Check installed version

apt-cache policy unitrends-backup || rpm -q unitrends-backup || unitrends-backup --version

2. UPGRADE to 10.5.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade unitrends-backup

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade unitrends-backup

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 10.0 (Debian / Ubuntu)

apt-cache madison unitrends-backup sudo apt install unitrends-backup=<VERSION_BEFORE_10.0> sudo apt-mark hold unitrends-backup

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list unitrends-backup sudo dnf downgrade unitrends-backup-<VERSION_BEFORE_10.0> sudo dnf versionlock add unitrends-backup

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · 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-2021-43039?

unitrends backup: upgrade to 10.5.5. Exact commands for each OS are on this page.

Is CVE-2021-43039 being exploited?

CVE-2021-43039 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-2021-43039 affect?

CVE-2021-43039 affects unitrends backup. Severity is medium (CVSS 6.5). An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. The Samba file sharing service allowed anonymous read/write access.

How urgent is CVE-2021-43039?

Priority 50/100. Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Samba vulnerabilities

Related CVEs

CVE-2021-43044 CRITICAL 9.8 UPGRADE An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5
CVE-2021-43043 MEDIUM 6.5 UPGRADE An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5
CVE-2021-43042 CRITICAL 9.8 UPGRADE An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5
CVE-2021-43041 HIGH 8.8 UPGRADE An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5
CVE-2021-43040 HIGH 8.8 UPGRADE An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5

References

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