CVE-2021-43039Public exploitNetwork attack vector

Unauthenticated file access via writable SMB shares

Published Dec 6, 2021 · Updated Aug 4, 2024

Improper access control in Kaseya Unitrends Backup Appliance 10.0.x through 10.5.4 allows remote attackers to read and write SMB shares. The appliance's Samba service accepts SMB null sessions and grants share read/write permissions instead of requiring authentication. Network access to the SMB service is sufficient, enabling unauthenticated disclosure or modification of files stored in exposed shares.

CVSS severity6.5
Medium
EPSS probability1.22%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper access control in Kaseya Unitrends Backup Appliance 10.0.x through 10.5.4 allows remote attackers to read and write SMB shares. The appliance's Samba service accepts SMB null sessions and grants share read/write permissions instead of requiring authentication. Network access to the SMB service is sufficient, enabling unauthenticated disclosure or modification of files stored in exposed shares.

The record

CVE
CVE-2021-43039
Published
Dec 6, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1021.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 6, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
6.4NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1021.002Remote Services: SMB/Windows Admin Shares

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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