Hackers have targeted some Cisco customers using a new vulnerability found thanks to leaked NSA cyber tools.

The tools were released in August by a hacker group dubbed ShadowBrokers and are confirmed to belong to the Equation Group which has strong ties with the NSA. It is the second such vulnerability to be found by Cisco as a result of the data dump made by the hackers; Cisco has already fixed a flaw in the SNMP implementation in its ASA firewalls.

Cisco has warned its customers that all versions of its IOS, IOS XE and IOS XR software are vulnerable to one of the many exploits released on August 15. The networking firm hasn't revealed which of its customers may have already been breached but the issue impacts firewalls, routers and switches made by the firm, enabling hackers to get hold of critical and confidential information from its customers.

"The vulnerability is due to insufficient condition checks in the part of the code that handles IKEv1 security negotiation requests. An attacker could exploit this vulnerability by sending a crafted IKEv1 packet to an affected device configured to accept IKEv1 security negotiation requests," the firm said in a security advisory blog.