CVE-2025-54353 is a Cross-site Scripting (XSS) vulnerability classified under CWE-79 that affects Fortinet FortiSandbox versions 4.0.0 through 5.0.2. The vulnerability arises from improper neutralization of input during web page generation, allowing an attacker to inject malicious scripts via crafted HTTP requests. This flaw enables remote attackers to execute unauthorized code or commands within the context of the victim's browser session when the victim interacts with the malicious content. The vulnerability does not require any authentication or privileges, increasing its attack surface. However, user interaction is necessary to trigger the exploit, typically by convincing a user to click a malicious link or visit a crafted webpage. The CVSS v3.1 base score is 5.3, reflecting medium severity, with the vector indicating network attack vector, low attack complexity, no privileges required, user interaction required, and impacts on confidentiality and integrity but not availability. No known exploits have been reported in the wild as of the publication date. FortiSandbox is a security appliance used for advanced threat detection and sandboxing, often deployed in enterprise and critical infrastructure environments to analyze suspicious files and URLs. Exploitation could lead to unauthorized script execution, potentially allowing attackers to steal session tokens, manipulate user sessions, or perform actions on behalf of the user within the FortiSandbox management interface or related web applications. This could undermine the integrity of threat analysis and response processes. The vulnerability affects multiple major versions, indicating a broad impact across organizations using FortiSandbox for threat detection and mitigation.

For European organizations, the impact of CVE-2025-54353 could be significant, especially for those relying on FortiSandbox for advanced threat detection and malware analysis. Successful exploitation could lead to unauthorized code execution in the context of the web management interface, potentially allowing attackers to hijack user sessions, steal sensitive information, or manipulate sandbox analysis results. This undermines the reliability of threat detection and response, increasing the risk of undetected malware or false negatives. Confidentiality and integrity of security operations data could be compromised, which is critical for organizations in regulated sectors such as finance, healthcare, and government. Although availability is not directly impacted, the loss of trust in sandbox results could delay incident response and remediation efforts. The requirement for user interaction somewhat limits the attack vector but does not eliminate risk, as phishing or social engineering could be used to trigger the exploit. The absence of known exploits in the wild reduces immediate risk but does not preclude future attacks, especially as threat actors often develop exploits after public disclosure. Organizations with high-value targets or critical infrastructure are particularly vulnerable due to the potential cascading effects of compromised threat detection capabilities.

European organizations should implement the following specific mitigations: 1) Monitor Fortinet's official channels for patches addressing CVE-2025-54353 and apply them promptly across all affected FortiSandbox versions. 2) Until patches are available, restrict access to the FortiSandbox web interface to trusted networks and users only, using network segmentation and firewall rules. 3) Employ web application firewalls (WAFs) with rules designed to detect and block XSS attack patterns targeting FortiSandbox interfaces. 4) Educate users with access to FortiSandbox about phishing and social engineering risks to reduce the likelihood of user interaction triggering the exploit. 5) Implement Content Security Policy (CSP) headers on the FortiSandbox web interface to limit script execution sources and reduce XSS impact. 6) Regularly audit and monitor logs for suspicious HTTP requests or anomalous user activity indicative of attempted exploitation. 7) Use multi-factor authentication (MFA) for FortiSandbox access to mitigate session hijacking risks post-exploitation. 8) Consider deploying endpoint protection solutions that can detect and block malicious scripts or payloads resulting from XSS attacks. These targeted measures go beyond generic advice and focus on reducing attack surface, limiting exposure, and enhancing detection capabilities.