CVE-2026-9780 in NetVault Backup
Summary
by MITRE • 06/25/2026
Quest NetVault Backup addclient3 Cross-Site Scripting Authentication Bypass Vulnerability. This vulnerability allows remote attackers to bypass authentication on affected installations of Quest NetVault Backup. User interaction is required to exploit this vulnerability in that the target must visit a malicious page or open a malicious file.
The specific flaw exists within the addclient3 webpage. The issue results from the lack of proper validation of user-supplied data, which can lead to the injection of an arbitrary script. An attacker can leverage this in conjunction with other vulnerabilities to execute arbitrary code in the context of SYSTEM. Was ZDI-CAN-27666.
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Analysis
by VulDB Data Team • 06/26/2026
This vulnerability represents a critical security flaw in Quest NetVault Backup software that combines cross-site scripting with authentication bypass capabilities. The issue is specifically located within the addclient3 webpage component of the backup solution, making it a targeted attack vector for malicious actors seeking to compromise enterprise backup infrastructure. The vulnerability was assigned the identifier ZDI-CAN-27666 and demonstrates how seemingly isolated flaws can compound to create severe operational risks when combined with other exploitation techniques.
The core technical weakness stems from insufficient input validation mechanisms within the addclient3 webpage interface. When user-supplied data is processed without proper sanitization or validation, attackers can inject malicious scripts that execute in the context of legitimate users' sessions. This cross-site scripting vulnerability operates under the CWE-79 classification as a classic injection flaw where untrusted data flows into web page rendering without adequate filtering. The vulnerability's authentication bypass capability means that even if users are properly authenticated, the XSS payload can be leveraged to escalate privileges or gain unauthorized access to system resources.
The operational impact of this vulnerability extends beyond simple script execution as it enables attackers to manipulate backup operations and potentially compromise entire backup environments. Since the exploitation requires user interaction through visiting malicious pages or opening infected files, attackers must rely on social engineering techniques to initiate the attack chain. However, once successfully exploited, the vulnerability can allow remote code execution with SYSTEM privileges, making it particularly dangerous for enterprise environments where backup systems often contain sensitive operational data and have elevated system access rights. This scenario aligns with ATT&CK technique T1059.007 for command and scripting interpreter usage, specifically targeting script-based attacks against web applications.
Organizations utilizing Quest NetVault Backup must implement immediate mitigation strategies to protect their infrastructure from exploitation attempts. The most effective approach involves applying vendor-provided security patches and updates as soon as they become available through official support channels. Network segmentation and web application firewalls can provide additional protection layers by monitoring and filtering suspicious traffic patterns associated with XSS attacks. Regular security assessments should include testing for similar input validation vulnerabilities across all web-based administrative interfaces, particularly focusing on components that handle user-supplied data in backup and recovery systems. The vulnerability demonstrates the importance of maintaining comprehensive patch management programs and implementing defense-in-depth strategies that protect critical infrastructure components from both external and internal threats.