Source: cve@mitre.org
Cross-site scripting (XSS) vulnerability in httpd/cgi-bin/vpn.cgi/vpnconfig.dat in Smoothwall Express 3.0 SP3 allows remote attackers to inject arbitrary web script or HTML via the COMMENT parameter in an Add action.
Smoothwall Express 3.0 SP3 is vulnerable to a critical cross-site scripting (XSS) flaw. Attackers can inject malicious HTML or JavaScript into the vpnconfig.dat configuration file through the COMMENT parameter, potentially leading to account compromise and system takeover.
Step 1: Payload Delivery: The attacker crafts a malicious HTTP request to httpd/cgi-bin/vpn.cgi/vpnconfig.dat with the action=Add parameter and a crafted COMMENT parameter containing the XSS payload (e.g., <script>alert('XSS')</script>).
Step 2: Server Processing: The Smoothwall server receives the request and processes it. The vpn.cgi script parses the request parameters.
Step 3: Data Storage: The script writes the attacker-supplied COMMENT value, including the malicious script, into the vpnconfig.dat configuration file.
Step 4: User Interaction: A legitimate user accesses the Smoothwall web interface, which displays information from the vpnconfig.dat file.
Step 5: Payload Execution: The web interface renders the contents of vpnconfig.dat, including the attacker's injected JavaScript. The user's browser executes the malicious script.
Step 6: Attack Outcome: The attacker's script executes within the user's browser, enabling actions such as cookie theft, session hijacking, or redirection to a phishing site.
The vulnerability stems from insufficient input validation and output encoding of the COMMENT parameter within the httpd/cgi-bin/vpn.cgi/vpnconfig.dat script. When an 'Add' action is performed, the script directly incorporates the user-supplied COMMENT value into the configuration file without proper sanitization. This allows attackers to inject arbitrary HTML or JavaScript code. When a legitimate user subsequently accesses the Smoothwall web interface, the injected script executes within their browser, enabling attackers to steal credentials, redirect users, or perform other malicious actions. The root cause is a lack of input validation and output encoding (e.g., escaping special characters) on the COMMENT parameter before it's written to the configuration file and subsequently rendered in the web interface. This allows for the injection of malicious code that is then executed in the context of the user's browser.
While no specific APT groups are definitively linked to exploiting this vulnerability, its simplicity and the age of the vulnerability make it a likely target for opportunistic attackers and script kiddies. The CISA KEV status is likely to be low given the age and specific product. However, it is possible that it is included in some exploit kits.
Network traffic analysis: Look for suspicious HTTP requests to httpd/cgi-bin/vpn.cgi/vpnconfig.dat with the action=Add parameter and unusually long or complex COMMENT parameters.
Web server logs: Examine web server access logs for requests containing potentially malicious HTML or JavaScript within the COMMENT parameter.
File integrity monitoring: Monitor the vpnconfig.dat file for unexpected modifications.
SIEM alerts: Configure a Security Information and Event Management (SIEM) system to alert on suspicious patterns in web server logs or network traffic related to this vulnerability.
Upgrade to a patched version of Smoothwall Express (if available).
Implement input validation: Ensure that the COMMENT parameter is properly validated to filter out malicious characters and scripts.
Implement output encoding: Encode the COMMENT parameter when it's displayed in the web interface to prevent script execution.
Web Application Firewall (WAF): Deploy a WAF to filter malicious requests before they reach the vulnerable application.
Regular security audits: Conduct regular security audits and penetration testing to identify and address vulnerabilities.
Disable unnecessary features: If VPN configuration is not required, disable the VPN functionality to reduce the attack surface.