Cisco Security Advisory
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AV:N/AC:L/Au:N/C:N/I:N/A:P/E:F/RL:OF/RC:C
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A vulnerability in the DNS resolution function of the Cisco Web Security Appliance (WSA) could allow an unauthenticated, remote attacker to cause a partial denial of service (DoS) condition due to DNS name resolution failing through the device.
The vulnerability is due to the handling of DNS requests awaiting a DNS response when new, incoming DNS requests are received. An attacker could exploit this vulnerability by sending TCP proxy traffic to the WSA at a high rate. An exploit could allow the attacker to cause a partial DoS condition because DNS name resolution fails, which results in the client receiving a HTTP 503 ''Service Unavailable'' error.
Cisco has confirmed the vulnerability and released software updates.
To exploit the vulnerability, the attacker may need access to trusted or internal networks to send DNS queries to the targeted system. This access requirement could limit the likelihood of a successful exploit.
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 IDs CSCur32005 and CSCur07907 for registered users that contain additional details and up-to-date lists of affected product versions.
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Administrators are advised to apply the appropriate updates.
Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
Administrators are advised to implement physical security for production servers.
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Cisco customers with active contracts can obtain updates through the Software Center at the following link: Cisco. Cisco customers without contracts can obtain upgrades by contacting the Cisco Technical Assistance Center at 1-800-553-2447 or 1-408-526-7209 or via email at tac@cisco.com.
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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-Sep-09
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