CVE-2019-25373 in OPNsense
Summary
by MITRE • 02/15/2026
OPNsense 19.1 contains a stored cross-site scripting vulnerability that allows authenticated attackers to inject malicious scripts by submitting crafted input to the category parameter. Attackers can send POST requests to firewall_rules_edit.php with script payloads in the category field to execute arbitrary JavaScript in the browsers of other users accessing firewall rule pages.
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Analysis
by VulDB Data Team • 02/20/2026
This vulnerability exists within OPNsense version 19.1 and represents a critical stored cross-site scripting flaw that enables authenticated attackers to inject malicious code into the system. The vulnerability specifically targets the firewall_rules_edit.php endpoint where the category parameter fails to properly sanitize user input, creating an avenue for persistent script injection attacks. The flaw allows attackers who have authenticated access to the system to submit crafted POST requests containing malicious JavaScript payloads within the category field, which then gets stored in the application's database and executed whenever other users view the affected firewall rule pages.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding mechanisms within the web application's processing pipeline. When the system processes the category parameter during firewall rule creation or modification, it does not adequately filter or escape special characters that could be interpreted as executable script code. This failure to implement proper sanitization techniques creates a persistent XSS vector where malicious scripts become permanently stored within the application's data layer. The vulnerability operates under CWE-79 which specifically addresses Cross-Site Scripting flaws in software applications, and aligns with ATT&CK technique T1566.001 for initial access through spearphishing attachments, though in this case the attack vector involves authenticated access rather than social engineering.
The operational impact of this vulnerability extends beyond simple script execution as it provides attackers with the ability to manipulate user sessions, steal authentication tokens, and potentially escalate privileges within the firewall management interface. When other administrators or users access the affected firewall rule pages, their browsers execute the injected JavaScript code, which could redirect them to malicious sites, harvest session cookies, or perform actions on their behalf. This creates a persistent threat that remains active until the malicious code is manually removed from the system, making it particularly dangerous in multi-user environments where multiple administrators might be affected. The stored nature of the vulnerability means that the malicious payload can affect any user who views the compromised data, regardless of whether they are authenticated or not.
Mitigation strategies for this vulnerability require immediate patching of the OPNsense system to version 19.1.12 or later, which contains the necessary fixes to properly sanitize the category parameter input. Organizations should also implement network segmentation and access controls to limit the number of users with administrative privileges, reducing the attack surface for authenticated XSS exploitation. Additional protective measures include implementing Content Security Policy headers to prevent execution of unauthorized scripts, regular monitoring of firewall rule modifications, and conducting security audits of stored data within web applications. The vulnerability demonstrates the importance of input validation and output encoding as fundamental security controls, emphasizing the need for comprehensive security testing including dynamic application security testing and manual penetration testing to identify similar stored XSS vulnerabilities in other components of the system.