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AUSCERT External Security Bulletin Redistribution
ESB-2015.2373
Cisco Web Security Appliance DNS Resolution Vulnerability
10 September 2015
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco Web Security Appliance
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2015-6287
Original Bulletin:
http://tools.cisco.com/security/center/viewAlert.x?alertId=40846
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Vulnerability Alert
Cisco Web Security Appliance DNS Resolution Vulnerability
Threat Type: CWE-399: Resource Management Errors
IntelliShield ID: 40846
Version: 1
First Published: 2015 September 09 12:38 GMT
Last Published: 2015 September 09 12:38 GMT
Port: Not available
CVE: CVE-2015-6287
Urgency: Unlikely Use
Credibility: Confirmed
Severity: Mild Damage
CVSS Base: 5.0
CVSS Temporal: 4.1
Version Summary: Cisco Web Security Appliance contains a vulnerability
that could allow an unauthenticated, remote attacker to cause a denial of
service condition. Updates are available.
Description
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.
Warning Indicators
At the time this alert was first published, Cisco WSA versions 8.0.6-078 and
8.0.6-115 were vulnerable. Later versions of Cisco WSA may also be affected.
IntelliShield Analysis
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.
Vendor Announcements
Cisco has released bug IDs CSCur32005 and CSCur07907 for registered users
that contain additional details and up-to-date lists of affected product
versions.
Impact
An unauthenticated, remote attacker could exploit this vulnerability
to cause a DoS condition due to DNS name resolution failure through
the affected device. This could result in the client receiving an HTTP
"Service Unavailable" error.
Technical Information
The vulnerability is due to the handling of DNS requests awaiting a DNS
response when new, incoming DNS requests are received.
An unauthenticated, remote attacker could exploit this vulnerability by
sending TCP proxy traffic to the WAS at a high rate. An exploit could allow
the attacker to cause a DoS condition due to DNS name resolution fails, which
could result in the client receiving an HTTP "Service Unavailable" error.
Safeguards
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.
Patches/Software
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.
Alert History
Initial Release
Product Sets
The security vulnerability applies to the following combinations of products.
Primary Products:
Cisco Cisco Web Security Appliance (WSA) 8.0 Base, .5, .5 Hot Patch
1, .6
Associated Products:
N/A
LEGAL DISCLAIMER
The urgency and severity ratings of this alert are not tailored to
individual users; users may value alerts differently based upon their
network configurations and circumstances. THE ALERT, AND INFORMATION
CONTAINED THEREIN, ARE PROVIDED ON AN "AS IS" BASIS AND DO NOT IMPLY ANY
KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY
OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE ALERT, AND INFORMATION
CONTAINED THEREIN, OR MATERIALS LINKED FROM THE ALERT, IS AT YOUR OWN
RISK. INFORMATION IN THIS ALERT AND ANY RELATED COMMUNICATIONS IS BASED ON
OUR KNOWLEDGE AT THE TIME OF PUBLICATION AND IS SUBJECT TO CHANGE WITHOUT
NOTICE. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.
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