A vulnerability in the SSL/TLS session handler of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to a memory leak when closing SSL/TLS connections in a specific state. An attacker could exploit this vulnerability by establishing several SSL/TLS sessions and ensuring they are closed under certain conditions. A successful exploit could allow the attacker to exhaust memory resources in the affected device, which would prevent it from processing new SSL/TLS connections, resulting in a DoS. Manual intervention is required to recover an affected device.
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Adaptive_security_appliance | Cisco | * | 9.6 (excluding) |
| Firepower_threat_defense | Cisco | * | 6.3.0.6 (excluding) |
| Firepower_threat_defense | Cisco | 6.4.0 (including) | 6.4.0.10 (excluding) |
| Firepower_threat_defense | Cisco | 6.5.0 (including) | 6.6.1 (excluding) |
| Adaptive_security_appliance_software | Cisco | 9.8.0 (including) | 9.8.4.26 (excluding) |
| Adaptive_security_appliance_software | Cisco | 9.9.0 (including) | 9.9.2.80 (excluding) |
| Adaptive_security_appliance_software | Cisco | 9.10.0 (including) | 9.10.1.44 (excluding) |
| Adaptive_security_appliance_software | Cisco | 9.12.0 (including) | 9.12.4.4 (excluding) |
| Adaptive_security_appliance_software | Cisco | 9.13.0 (including) | 9.13.1.13 (excluding) |
| Adaptive_security_appliance_software | Cisco | 9.14.0 (including) | 9.14.1.19 (excluding) |
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.