CVE-2025-70519 in Fanvil
Summary
by MITRE • 10/07/2026
The device log component of Fanvil x7a firmware version 2.6.0.1182 does not properly sanitize or encode reflected user supplied data. The lack of sanitization allows for the injection of HTML which can be used to execute malicious JavaScript code on any target browser which renders the device log component.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/07/2026
The vulnerability identified in Fanvil x7a firmware version 2.6.0.1182 represents a classic instance of Cross-Site Scripting, specifically categorized under CWE-79: Improper Neutralization of Input During Web Page Generation. This flaw resides within the device log component, which is responsible for displaying operational logs to administrators or users via a web interface. The core technical deficiency lies in the application's failure to properly sanitize or encode user-supplied data before rendering it back into the HTML document structure. When an attacker inputs malicious content that includes script tags or event handlers, the server processes this input without applying necessary security filters such as output encoding or context-aware escaping. Consequently, when another user accesses the log view through a web browser, the browser interprets the injected code not as static text but as executable JavaScript instructions.
From an operational perspective, this vulnerability allows for remote code execution within the context of the victim's browser session. An attacker can craft a malicious link or manipulate input fields to trigger the injection when the target user views the logs. Once executed, the malicious script operates with the same privileges and permissions as the legitimate application running in that browser tab. This capability enables a range of hostile actions including but not limited to stealing sensitive authentication cookies, session tokens, or multi-factor authentication codes associated with the device management interface. It also facilitates keylogging capabilities where every keystroke entered by the administrator can be captured and exfiltrated to an external server controlled by the attacker. Furthermore, the script could perform unauthorized administrative actions on behalf of the user, such as changing network configurations, disabling security features, or initiating firmware updates without proper authorization checks.
The impact extends beyond simple data theft due to the potential for session hijacking. If the web interface relies heavily on cookie-based authentication and lacks robust anti-CSRF protections alongside this XSS flaw, an attacker can fully impersonate a legitimate administrator. This compromises the confidentiality, integrity, and availability of the VoIP infrastructure managed by the Fanvil device. Attackers could redirect calls to premium rate numbers, intercept sensitive voice communications if real-time data is exposed through other vectors enabled by the compromised session, or disrupt service by altering SIP settings. The vulnerability aligns with MITRE ATT&CK technique T1059 Command and Scripting Interpreter, specifically JavaScript execution within a browser environment, which serves as an initial access vector for deeper network penetration.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary fix involves implementing strict input validation on the server side to reject any non-alphanumeric characters or specific HTML entities in log entries where they are not expected. More critically, output encoding must be enforced using context-aware methods such as HTML entity encoding for data rendered within HTML bodies, attribute values, and script blocks. Developers should adopt a whitelist approach rather than relying solely on blacklist filters which can often be bypassed through obfuscation techniques like double encoding or Unicode variations. Additionally, implementing Content Security Policy headers can significantly reduce the impact of successful XSS attacks by restricting the sources from which scripts are allowed to load and execute. Upgrading to firmware versions that have patched this specific sanitization logic is essential for restoring security posture until permanent code-level fixes are deployed across all instances of the affected hardware model.