Three models of Cisco wireless VPN firewalls and routers from the small business RV series contain a critical unpatched vulnerability that attackers can exploit remotely to take control of devices.The vulnerability is located in the Web-based management interface of the Cisco RV110W Wireless-N VPN Firewall, RV130W Wireless-N Multifunction VPN Router and RV215W Wireless-N VPN Router.It can be easily exploited if the affected devices are configured for remote management since attackers only need to send an unauthenticated HTTP request with custom user data. This will result in remote code execution as root, the highest privileged account on the system, and can lead to a complete compromise.Cisco Systems warned about the vulnerability in a security advisory Wednesday, but no patches are yet available. The company plans to release firmware updates that will address this flaw on affected models sometime in the third quarter of 2016.Worse yet, this is not the only unpatched vulnerability that exists in these three Cisco devices. The company also warned of a medium-severity, cross-site scripting (XSS) flaw and two medium-risk buffer overflows that could result in denial-of-service conditions.While exploiting the buffer overflows requires attackers to have an authenticated session in the device's Web-based interface, the XSS flaw can be triggered by tricking authenticated users to click on specifically crafted URLs."A successful exploit could allow the attacker to execute arbitrary script in the context of the web-based management interface for the device or allow the attacker to access sensitive browser-based information," Cisco said in an advisory.The XSS flaw makes it difficult for users to find a mitigation strategy in the absence of patches, because it can be combined with the other vulnerabilities. For example, if users disable external management in their devices in order to protect them from the critical vulnerability, the devices will still be exposed through the cross-site scripting flaw.