Cisco Security Advisory
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AV:N/AC:L/Au:N/C:P/I:N/A:N/E:F/RL:U/RC:C
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A vulnerability in the Unicast Reverse Path Forwarding (uRPF) feature in the Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to bypass the uRPF validation checks.
The vulnerability is due to incorrect uRPF validation where IP packets from an outside interface, whose IP address is both in the ASA routing table and associated with an internal interface, are not dropped. An attacker could exploit this vulnerability by sending spoofed IP packets to the ASA in a subnet range that should be dropped. An exploit could allow the attacker to bypass uRPF validation on the ASA and the packet will be incorrectly forwarded on the internal network.
Cisco has confirmed the vulnerability; however, software updates are not available.
To exploit this vulnerability, the targeted device must have the ip verfiy reverse-path interface command set on an outside interface and the interface must have a default route configured. In addition, the attacker must know a subnet range set on the targeted device that is configured to drop packets prior to sending spoofed IP packets to the device.
Cisco indicates through the CVSS score that functional exploit code exists; however, the code is not known to be publicly available.
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Cisco has released bug ID CSCuv60724 for registered users, which contains additional details and an up-to-date list of affected product versions.
Vulnerable Products
At the time this alert was first published, Cisco ASA Software Releases 9.3(1.50), 9.3(2.100), 9.3(3), and 9.4(1) were vulnerable. Later releases of Cisco ASA Software may also be vulnerable.Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by these vulnerabilities.
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Administrators are advised to contact the vendor regarding future updates and releases.
Administrators can help protect affected systems from external attacks by using a solid firewall strategy.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators are advised to monitor affected systems.
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Software updates are not available.
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The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.0 Initial Release NA Final 2015-Aug-12
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