Fortinet has announced a significant security vulnerability within its FortiSandbox product that could permit unauthorized access to the virtual machine VNC servers used in malware scanning processes. Identified as CVE-2026-59835, this vulnerability is rated with a CVSSv3 score of 7.7, indicating its high severity.
Details of the Vulnerability
The flaw is categorized under CWE-668 as an Exposure of Resource to Wrong Sphere. It enables attackers to craft specific network requests that grant access to the VNC server linked with scanning virtual machines, bypassing any credential requirements. This presents a risk of information exposure due to the low complexity required for executing the attack and the absence of user interaction.
FortiSandbox’s design, which utilizes isolated virtual machines for the purpose of safely detonating and analyzing suspicious files, is compromised by this vulnerability. Unauthorized access to these VNC servers could allow attackers to observe or manipulate the sandboxed environments, jeopardizing the integrity of malware analysis efforts and potentially exposing sensitive data.
Versions Affected and Mitigation Measures
Specific versions of FortiSandbox are impacted. FortiSandbox version 5.0, specifically builds 5.0.0 through 5.0.2, requires an upgrade to version 5.0.3 or later. Similarly, version 4.4 builds 4.4.3 through 4.4.8 should be updated to 4.4.9 or above. It is important to note that FortiSandbox PaaS deployments remain unaffected, so no action is necessary for those users.
However, organizations using the on-premises hardware models FSA-500G and FSA-1500G are urged to apply patches promptly to mitigate potential risks. Fortinet has recognized the INPS security team for their role in discovering and responsibly disclosing this vulnerability in accordance with the company’s coordinated disclosure protocol.
Recent Security Concerns with FortiSandbox
This vulnerability disclosure is part of a series of security issues Fortinet has tackled within the FortiSandbox platform this year. Previous vulnerabilities include a critical OS command injection flaw (CVE-2026-25089) with a CVSS score of 9.1, and a missing authorization issue in the Web UI, both of which also allowed remote, unauthenticated attackers to compromise the system.
As of the advisory FG-IR-26-145 published on July 14, 2026, there have been no reports of this latest vulnerability being exploited in live environments. Organizations are advised to stay vigilant and ensure their systems are updated to protect against these threats.
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