Cisco has warned owners of its Cisco Small Business SPA 300 and 500 Series IP phones, about a vulnerability of the device sthat could allow an unauthenticated, remote attacker to access sensitive information. According to a security advisory released by Cisco, a vulnerability in the firmware of the Cisco Small Business SPA 300 and 500 series IP phones could allow an unauthenticated, remote attacker to listen to the audio stream of an IP phone.

The vulnerability is due to improper authentication settings in the default configuration. An attacker could exploit this vulnerability by sending a crafted XML request to the affected device. An exploit could allow the attacker to listen to a remote audio stream or make phone calls remotely.

Cisco has confirmed that the Cisco Small Business SPA 300 and 500 Series IP phones version 7.5.5 are vulnerable. But later versions of Cisco Small Business SPA 300 and 500 Series IP phones may also be vulnerable, the company said.

No software updates are available yet.

To exploit this vulnerability, an attacker may need access to trusted, internal networks behind a firewall to send crafted XML requests to the targeted device. This access requirement may reduce the likelihood of a successful exploit.

Cisco advices administrators to enable XML Execution authentication in the configuration settings of affected devices. They can also help protect affected systems from external attacks by using a solid firewall strategy. In adition, admins may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.