A vulnerability in the handling of RSA keys on devices running Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to retrieve an RSA private key. This vulnerability is due to a logic error when the RSA key is stored in memory on a hardware platform that performs hardware-based cryptography. An attacker could exploit this vulnerability by using a Lenstra side-channel attack against the targeted device. Approximately 5 percent of the RSA keys on a device that is running a vulnerable release of Cisco ASA Software or Cisco FTD Software are expected to be affected. If an attacker obtains the RSA private key, they could use the key to impersonate a device that is running Cisco ASA Software or Cisco FTD Software or to decrypt the device traffic.