CVE-2026-1791 identifies a vulnerability in Hillstone Networks Operation and Maintenance Security Gateway version V5.5ST00001B113 running on Linux systems. The issue is categorized under CWE-434, which involves the unrestricted upload of files with dangerous types. This vulnerability allows an attacker with high privileges to upload arbitrary files, including web shells, to the web server component of the gateway. Such an upload could enable attackers to execute unauthorized commands or scripts remotely, potentially disrupting service availability or facilitating further attacks. The vulnerability does not directly compromise confidentiality or integrity but can degrade availability by enabling denial of service or unauthorized control over the gateway. The CVSS 3.1 score is 2.7, reflecting the requirement for high privileges (PR:H), no user interaction (UI:N), network attack vector (AV:N), and limited impact on confidentiality, integrity, and availability (C:N/I:N/A:L). No known public exploits or patches are currently available, indicating the vulnerability is newly disclosed and not yet actively exploited. The affected product is a security gateway used for operation and maintenance tasks, which is critical in network security infrastructure. The unrestricted file upload stems from insufficient validation or filtering of uploaded file types, allowing dangerous payloads to be placed on the server. This vulnerability highlights the importance of strict input validation and access control in security appliances.

For European organizations, the impact of CVE-2026-1791 is primarily on availability and operational continuity. Organizations relying on Hillstone Networks Operation and Maintenance Security Gateway for network security and management could face service disruptions if attackers exploit this vulnerability to upload web shells and execute malicious code. Although exploitation requires high privileges, insider threats or compromised administrative accounts could leverage this flaw to escalate attacks. The lack of impact on confidentiality and integrity reduces the risk of data breaches directly from this vulnerability, but availability degradation could affect critical infrastructure and business operations. Given the role of such gateways in perimeter defense and network monitoring, successful exploitation could also facilitate lateral movement or further compromise within the network. European sectors with stringent uptime and security requirements, such as finance, telecommunications, and critical infrastructure, may experience operational risks. The absence of known exploits reduces immediate threat but does not eliminate the need for vigilance and proactive mitigation.

To mitigate CVE-2026-1791, European organizations should implement the following specific measures: 1) Restrict file upload functionality on the affected Hillstone product by enforcing strict file type validation and whitelisting only safe file extensions. 2) Apply the principle of least privilege to administrative accounts to minimize the risk of high-privilege compromise. 3) Monitor file upload directories and web server logs for unusual or unauthorized file uploads, especially web shells or scripts. 4) Employ network segmentation to isolate management interfaces of the security gateway from general user networks. 5) Use application-layer firewalls or intrusion detection systems to detect and block suspicious upload attempts. 6) Regularly audit and update access control policies on the gateway to ensure only authorized personnel can perform uploads. 7) Engage with Hillstone Networks for updates or patches and apply them promptly once available. 8) Conduct internal security awareness training focusing on risks associated with privileged account misuse. These targeted actions go beyond generic advice by focusing on the specific upload vector and administrative controls relevant to this vulnerability.