A vulnerability in the web proxy functionality of Cisco AsyncOS Software for Cisco Web Security Appliances could allow an unauthenticated, remote attacker to exhaust system memory and cause a denial of service (DoS) condition on an affected system. The vulnerability exists because the affected software improperly manages memory resources for TCP connections to a targeted device. An attacker could exploit this vulnerability by establishing a high number of TCP connections to the data interface of an affected device via IPv4 or IPv6. A successful exploit could allow the attacker to exhaust system memory, which could cause the system to stop processing new connections and result in a DoS condition. System recovery may require manual intervention. Cisco Bug IDs: CSCvf36610.
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Web_security_appliance | Cisco | 9.1.1-074 (including) | 9.1.1-074 (including) |
| Web_security_appliance | Cisco | 9.1.2-010 (including) | 9.1.2-010 (including) |
| Web_security_appliance | Cisco | 9.1.2-022 (including) | 9.1.2-022 (including) |
| Web_security_appliance | Cisco | 9.1.2-039 (including) | 9.1.2-039 (including) |
| Web_security_appliance | Cisco | 10.1.0-204 (including) | 10.1.0-204 (including) |
| Web_security_appliance | Cisco | 10.1.1-235 (including) | 10.1.1-235 (including) |
| Web_security_appliance | Cisco | 10.5.1-270 (including) | 10.5.1-270 (including) |
| Web_security_appliance | Cisco | 10.5.1-296 (including) | 10.5.1-296 (including) |
| Web_security_appliance | Cisco | 10.5.2-042 (including) | 10.5.2-042 (including) |
| Web_security_appliance | Cisco | 11.0.0-641 (including) | 11.0.0-641 (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.