A vulnerability in the SSH server of Cisco Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition for the SSH server of an affected device. This vulnerability is due to a logic error when an SSH session is established. An attacker could exploit this vulnerability by sending crafted SSH messages to an affected device. A successful exploit could allow the attacker to exhaust available SSH resources on the affected device so that new SSH connections to the device are denied, resulting in a DoS condition. Existing SSH connections to the device would continue to function normally. The device must be rebooted manually to recover. However, user traffic would not be impacted and could be managed using a remote application such as Cisco Adaptive Security Device Manager (ASDM).
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Adaptive_security_appliance_software | Cisco | 9.16.4.67 (including) | 9.16.4.67 (including) |
| Adaptive_security_appliance_software | Cisco | 9.16.4.70 (including) | 9.16.4.70 (including) |
| Adaptive_security_appliance_software | Cisco | 9.18.4.40 (including) | 9.18.4.40 (including) |
| Adaptive_security_appliance_software | Cisco | 9.20.3 (including) | 9.20.3 (including) |
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.