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Vulnerability record · CVE-2021-43042 · published 6 December 2021

CVE-2021-43042: Kaseya unitrends backup classic buffer overflow vulnerability

Kaseya · Unitrends Backup

An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. A buffer overflow existed in the vaultServer component. This was exploitable by a remote unauthenticated attacker.

9.8 CVSS 3.1 Critical EPSS 2.9% · top 13.6% CWE-120 · Classic buffer overflow
9.8CVSS 3.1 base score, v2 7.5
2.9%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References, 4 tagged exploit
17 Jun 2026Last modified by NVD

Description

An issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. A buffer overflow existed in the vaultServer component. This was exploitable by a remote unauthenticated attacker.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://helpdesk.kaseya.com/hc/en-gb/articles/4412762258961 Vendor Advisory
https://www.cyberonesecurity.com/blog/exploiting-kaseya-unitrends-backup-appliance-part-1 ExploitThird Party Advisory
https://www.cyberonesecurity.com/blog/exploiting-kaseya-unitrends-backup-appliance-part-2 ExploitThird Party Advisory
https://helpdesk.kaseya.com/hc/en-gb/articles/4412762258961 Vendor Advisory
https://www.cyberonesecurity.com/blog/exploiting-kaseya-unitrends-backup-appliance-part-1 ExploitThird Party Advisory
https://www.cyberonesecurity.com/blog/exploiting-kaseya-unitrends-backup-appliance-part-2 ExploitThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2021-40386Kaseya unitrends backup vulnerabilityKaseya Unitrends Client/Agent through 10.5,5 allows remote attackers to execute arbitrary code.EPSS 1.9%9.8CVE-2021-43033Kaseya unitrends backup os command injection vulnerabilityAn issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. Multiple functions in the bpserverd daemon were vulnerable to arbitrary r…EPSS 6.0%9.8CVE-2021-43035Kaseya unitrends backup sql injection vulnerabilityAn issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. Two unauthenticated SQL injection vulnerabilities were discovered, allowi…EPSS 3.3%9.8CVE-2021-43036Kaseya unitrends backup weak password requirements vulnerabilityAn issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. The password for the PostgreSQL wguest account is weak.EPSS 1.9%9.8CVE-2021-43044Kaseya unitrends backup hard-coded credentials vulnerabilityAn issue was discovered in Kaseya Unitrends Backup Appliance before 10.5.5. The SNMP daemon was configured with a weak default community.EPSS 1.9%9.8CVE-2018-6328Unitrends Backup authentication bypass leads to command injectionUnitrends Backup before 10.1.0 exposes a user interface vulnerable to an authentication bypass, allowing an unauthenticated user to reach the /api/ho…EPSS 64%analysed9.8CVE-2017-12477Unitrends Backup bpserverd authentication bypass allows root command executionThe bpserverd proprietary protocol in Unitrends Backup before 10.0.0, invoked through xinetd, can have its authentication bypassed. A remote attacker…EPSS 68%analysed9.8CVE-2017-12478Unitrends Backup api/storage auth bypass leads to root command executionThe api/storage web interface in Unitrends Backup before 10.0.0 fails to validate an input parameter, allowing authentication to be bypassed. Because…EPSS 78%analysed

Source: NIST National Vulnerability Database (record CVE-2021-43042), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.