Cisco Applied Mitigation Bulletin-
A vulnerability in Siemens SCALANCE X200 IRT Series Devices could allow an unauthenticated, remote attacker to gain unauthorized access. The vulnerability exists due to an implementation error in SNMPv3. This could allow the attacker to execute SNMP commands without the correct credentials on the targeted system. The attack vector is the SNMPv3 protocol over UDP port 161. This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2013-3634.
Additionally, a vulnerability in Siemens SCALANCE X200 IRT Series Devices could allow an authenticated, remote attacker to gain elevated privileges. The vulnerability exists because the device firmware fails to implement sufficient verifications on user-supplied commands. This could allow the attacker on an adjacent network to execute privileged commands on the targeted system through the web interface using an unprivileged account. This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2013-3633. There is no associated mitigation for CVE-2013-3633.
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Cisco IOS Software can provide effective means of exploit prevention using the following methods:
- Transit access control lists (tACLs)
- Unicast Reverse Path Forwarding (uRPF)
- IP Source Guard (IPSG)
The proper deployment and configuration of uRPF provides an effective means of protection against attacks that use packets with spoofed source IP addresses. Unicast RPF should be deployed as close to all traffic sources as possible.
The proper deployment and configuration of IPSG provides an effective means of protection against spoofed packets at the access layer.
Effective exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance, Cisco Catalyst 6500 Series ASA Services Module (ASASM), and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers using Application layer protocol inspection.
This protection mechanism filters and drops, as well as verifies the source IP address of, packets that are attempting to exploit the vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.
Cisco IOS Software, Cisco ASA, Cisco ASASM, and Cisco FWSM firewalls can provide visibility through syslog messages and counter values displayed in the output from show commands.
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Organizations are advised to follow their standard risk evaluation and mitigation processes to determine the potential impact of this vulnerability. Triage refers to sorting projects and prioritizing efforts that are most likely to be successful. Cisco has provided documents that can help organizations develop a risk-based triage capability for their information security teams. Risk Triage for Security Vulnerability Announcements and Risk Triage and Prototyping can help organizations develop repeatable security evaluation and response processes.
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Caution: The effectiveness of any mitigation technique depends on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. As with any configuration change, evaluate the impact of this configuration prior to applying the change.
Specific information about mitigation and identification is available for these devices:- Cisco IOS Routers and Switches
- Cisco IOS NetFlow and Cisco IOS Flexible NetFlow
- Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls
Cisco IOS Routers and Switches
Mitigation: Transit Access Control Lists
To protect the network from traffic that enters the network at ingress access points, which may include Internet connection points, partner and supplier connection points, or VPN connection points, administrators are advised to deploy transit access control lists (tACLs) to perform policy enforcement. Administrators can construct a tACL by explicitly permitting only authorized traffic to enter the network at ingress access points or permitting authorized traffic to transit the network in accordance with existing security policies and configurations. A tACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The tACL policy denies unauthorized SNMP IPv4 packets over UDP port 161 that are sent to affected devices. In the following example, 192.168.60.0/24 represents the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.
Additional information about tACLs is available in Transit Access Control Lists: Filtering at Your Edge.!-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable port and protocol ! access-list 150 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 161 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! access-list 150 deny udp any 192.168.60.0 0.0.0.255 eq 161 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Explicit deny for all other IP traffic ! access-list 150 deny ip any any ! !-- Apply tACLs to interfaces in the ingress direction ! interface GigabitEthernet0/0 ip access-group 150 in
Note that filtering with an interface access list will elicit the transmission of ICMP unreachable messages back to the source of the filtered traffic. Generating these messages could have the undesired effect of increasing CPU utilization on the device. In Cisco IOS Software, ICMP unreachable generation is limited to one packet every 500 milliseconds by default. ICMP unreachable message generation can be disabled using the interface configuration command no ip unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration command ip icmp rate-limit unreachable interval-in-ms.Identification: Transit Access Control Lists
After the administrator applies the tACL to an interface, the show ip access-lists command will identify the number of SNMP IPv4 packets on UDP port 161 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit this vulnerability. Example output for show ip access-lists 150 follows:router#show ip access-lists 150 Extended IP access list 150 10 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 161 20 deny udp any 192.168.60.0 0.0.0.255 eq 161 (12 matches) 30 deny ip any any router#In the preceding example, access list 150 has dropped 12 SNMP packets on UDP port 161 for access control list entry (ACE) line 20.
For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and Cisco IOS Router Syslog Events Cisco Security Intelligence Operations white paper.
Administrators can use the Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Cisco Security Intelligence Operations white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.Identification: Access List Logging
The log and log-input access control list (ACL) option will cause packets that match specific ACEs to be logged. The log-input option enables logging of the ingress interface in addition to the packet source and destination IP addresses and ports. Caution: Access control list logging can be very CPU intensive and must be used with extreme caution. Factors that drive the CPU impact of ACL logging are log generation, log transmission, and process switching to forward packets that match log-enabled ACEs.
For Cisco IOS Software, the ip access-list logging interval interval-in-ms command can limit the effects of process switching induced by IPv4 ACL logging. The logging rate-limit rate-per-second [except loglevel] command limits the impact of log generation and transmission.
The CPU impact from ACL logging can be addressed in hardware on the Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers with the Supervisor Engine 720 or the Supervisor Engine 32 using optimized ACL logging.
For additional information about the configuration and use of ACL logging, reference the Understanding Access Control List Logging Cisco Security Intelligence Operations white paper.
Mitigation: Spoofing Protection
Unicast Reverse Path Forwarding
The vulnerability described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure Unicast Reverse Path Forwarding (uRPF) as a protection mechanism against spoofing.
uRPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on uRPF to provide complete spoofing protection because spoofed packets may enter the network through a uRPF-enabled interface if an appropriate return route to the source IP address exists. Administrators are advised to take care to ensure that the appropriate uRPF mode (loose or strict) is configured during the deployment of this feature because it can drop legitimate traffic that is transiting the network. In an enterprise environment, uRPF may be enabled at the Internet edge and the internal access layer on the user-supporting Layer 3 interfaces.
Additional information is available in the Unicast Reverse Path Forwarding Loose Mode Feature Guide.
For additional information about the configuration and use of uRPF reference the Understanding Unicast Reverse Path Forwarding Cisco Security Intelligence Operations white paper.IP Source Guard
IP Source Guard (IPSG) is a security feature that restricts IP traffic on nonrouted, Layer 2 interfaces by filtering packets based on the DHCP snooping binding database and manually configured IP source bindings. Administrators can use IPSG to prevent attacks from an attacker who attempts to spoof packets by forging the source IP address and/or the MAC address. When properly deployed and configured, IPSG coupled with strict mode uRPF provides the most effective means of spoofing protection for the vulnerability described in this document.
Additional information about the deployment and configuration of IPSG is available in Configuring DHCP Features and IP Source Guard.Identification: Spoofing Protection Using Unicast Reverse Path Forwarding
With uRPF properly deployed and configured throughout the network infrastructure, administrators can use the show cef interface type slot/port internal, show ip interface, show cef drop, show ip cef switching statistics feature, and show ip traffic commands to identify the number of packets that uRPF has dropped.
Note: Beginning with Cisco IOS Software Release 12.4(20)T, the command show ip cef switching has been replaced by show ip cef switching statistics feature.
Note: The show command | begin regex and show command | include regex command modifiers are used in the following examples to minimize the amount of output that administrators will need to parse to view the desired information. Additional information about command modifiers is in the show command sections of the Cisco IOS Configuration Fundamentals Command Reference.router#show cef interface GigabitEthernet 0/0 internal | include drop ip verify: via=rx (allow default), acl=0, drop=18, sdrop=0 router#Note: show cef interface type slot/port internal is a hidden command that must be fully entered at the command-line interface. Command completion is not available for it.router#show cef drop CEF Drop Statistics Slot Encap_fail Unresolved Unsupported No_route No_adj ChkSum_Err RP 27 0 0 18 0 0 router# router#show ip interface GigabitEthernet 0/0 | begin verify IP verify source reachable-via RX, allow default, allow self-ping 18 verification drops 0 suppressed verification drops router# router#show ip cef switching statistics feature IPv4 CEF input features:
In the preceding show cef interface type slot/port internal, show cef drop, show ip interface type slot/port, show ip cef switching statistics feature, and show ip traffic examples, uRPF has dropped 18 IP packets received globally on all interfaces with uRPF configured because of the inability to verify the source address of the IP packets within the forwarding information base of Cisco Express Forwarding.
Path Feature Drop Consume Punt Punt2Host Gave route
RP PAS uRPF 18 0 0 0 0 Total 18 0 0 0 0 -- CLI Output Truncated -- router# router#show ip traffic | include RPF 18 no route, 18 unicast RPF, 0 forced drop router#
Cisco IOS NetFlow and Cisco IOS Flexible NetFlow
Identification: IPv4 Traffic Flow Identification Using Cisco IOS NetFlow
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of IPv4 traffic flows that may be attempts to exploit the vulnerability described in this document. Administrators are advised to investigate flows to determine whether they are attempts to exploit the vulnerability or whether they are legitimate traffic flows.router#show ip cache flow IP packet size distribution (90784136 total packets): 1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480 .000 .698 .011 .001 .004 .005 .000 .004 .000 .000 .003 .000 .000 .000 .000 512 544 576 1024 1536 2048 2560 3072 3584 4096 4608 .000 .001 .256 .000 .010 .000 .000 .000 .000 .000 .000 IP Flow Switching Cache, 4456704 bytes 1885 active, 63651 inactive, 59960004 added 129803821 ager polls, 0 flow alloc failures Active flows timeout in 30 minutes Inactive flows timeout in 15 seconds IP Sub Flow Cache, 402056 bytes 0 active, 16384 inactive, 0 added, 0 added to flow 0 alloc failures, 0 force free 1 chunk, 1 chunk added last clearing of statistics never Protocol Total Flows Packets Bytes Packets Active(Sec) Idle(Sec) -------- Flows /Sec /Flow /Pkt /Sec /Flow /Flow TCP-Telnet 11393421 2.8 1 48 3.1 0.0 1.4 TCP-FTP 236 0.0 12 66 0.0 1.8 4.8 TCP-FTPD 21 0.0 13726 1294 0.0 18.4 4.1 TCP-WWW 22282 0.0 21 1020 0.1 4.1 7.3 TCP-X 719 0.0 1 40 0.0 0.0 1.3 TCP-BGP 1 0.0 1 40 0.0 0.0 15.0 TCP-Frag 70399 0.0 1 688 0.0 0.0 22.7 TCP-other 47861004 11.8 1 211 18.9 0.0 1.3 UDP-DNS 582 0.0 4 73 0.0 3.4 15.4 UDP-NTP 287252 0.0 1 76 0.0 0.0 15.5 UDP-other 310347 0.0 2 230 0.1 0.6 15.9 ICMP 11674 0.0 3 61 0.0 19.8 15.5 IPv6INIP 15 0.0 1 1132 0.0 0.0 15.4 GRE 4 0.0 1 48 0.0 0.0 15.3 Total: 59957957 14.8 1 196 22.5 0.0 1.5 SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.10.201 Gi0/1 192.168.60.102 11 0984 00A1 1 Gi0/0 192.168.11.54 Gi0/1 192.168.60.158 11 0911 00A1 3 Gi0/1 192.168.150.60 Gi0/0 10.89.16.226 06 0016 12CA 1 Gi0/0 192.168.13.97 Gi0/1 192.168.60.28 11 0B3E 00A1 5 Gi0/0 192.168.10.17 Gi0/1 192.168.60.97 11 0B89 00A1 1 Gi0/0 10.88.226.1 Gi0/1 192.168.202.22 11 007B 007B 1 Gi0/0 192.168.12.185 Gi0/1 192.168.60.239 11 0BD7 00A1 1 Gi0/0 10.89.16.226 Gi0/1 192.168.150.60 06 12CA 0016 1In the preceding example, there are multiple flows for SNMP on UDP port 161 (hex value 00A1).
This traffic is sourced from and sent to addresses within the 192.168.60.0/24 address block, which is used by affected devices. The packets in these flows may be spoofed and may indicate an attempt to exploit this vulnerability. Administrators are advised to compare these flows to baseline utilization for SNMP traffic sent on UDP port 161 and also investigate the flows to determine whether they are sourced from untrusted hosts or networks.
As shown in the following example, to view only the traffic flows for SNMP packets on UDP port 161 (hex value 00A1), use the show ip cache flow | include SrcIf|_PrHex_.*00A1 command to display the related Cisco NetFlow records:
UDP Flowsrouter#show ip cache flow | include SrcIf|_11_.*00A1 SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.12.110 Gi0/1 192.168.60.163 11 092A 00A1 6 Gi0/0 192.168.11.230 Gi0/1 192.168.60.20 11 0C09 00A1 1 Gi0/0 192.168.11.131 Gi0/1 192.168.60.245 11 0B66 00A1 18 Gi0/0 192.168.13.7 Gi0/1 192.168.60.162 11 0914 00A1 1 Gi0/0 192.168.41.86 Gi0/1 192.168.60.27 11 0B7B 00A1 2
Identification: IPv4 Traffic Flow Identification Using Cisco IOS Flexible NetFlow
Introduced in Cisco IOS Software Releases 12.2(31)SB2 and 12.4(9)T, Cisco IOS Flexible NetFlow improves the original Cisco NetFlow by adding the capability to customize traffic analysis parameters for an administrator's specific requirements. Original Cisco NetFlow uses a fixed seven tuples of IP information to identify a flow, whereas Cisco IOS Flexible NetFlow allows the flow to be user defined. It facilitates the creation of more complex configurations for traffic analysis and data export by using reusable configuration components.
The following example output is from a Cisco IOS device that is running a version of Cisco IOS Software in the 15.1T train. Although the syntax will be almost identical for the 12.4T and 15.0 trains, it may vary slightly depending on the actual Cisco IOS release being used. In the following configuration, Cisco IOS Flexible NetFlow will collect information on interface GigabitEthernet0/0 for incoming IPv4 flows based on source IPv4 address, as defined by the match ipv4 source address key field statement. Cisco IOS Flexible NetFlow will also include nonkey field information about source and destination IPv4 addresses, protocol, ports (if present), ingress and egress interfaces, and packets per flow.! !-- Configure key and nonkey fields !-- in the user-defined flow record ! flow record FLOW-RECORD-ipv4 match ipv4 source address collect ipv4 protocol collect ipv4 destination address collect transport source-port collect transport destination-port collect interface input collect interface output collect counter packets ! !-- Configure the flow monitor to !-- reference the user-defined flow !-- record ! flow monitor FLOW-MONITOR-ipv4 record FLOW-RECORD-ipv4 ! !-- Apply the flow monitor to the interface !-- in the ingress direction ! interface GigabitEthernet0/0 ip flow monitor FLOW-MONITOR-ipv4 input
The Cisco IOS Flexible NetFlow flow output is as follows:router#show flow monitor FLOW-MONITOR-ipv4 cache format table Cache type: Normal Cache size: 4096 Current entries: 6 High Watermark: 1 Flows added: 9181 Flows aged: 9175 - Active timeout ( 1800 secs) 9000 - Inactive timeout ( 15 secs) 175 - Event aged 0 - Watermark aged 0 - Emergency aged 0 IPV4 SRC ADDR ipv4 dst addr trns src port trns dst port intf input intf output pkts ip prot ============== ============== ============= ============= ========== =========== ==== ======= 192.168.11.54 192.168.60.158 1123 161 Gi0/0 Gi0/1 2212 17 192.168.150.60 10.89.16.226 2567 443 Gi0/0 Gi0/1 13 6 192.168.10.17 192.168.60.97 4231 161 Gi0/0 Gi0/1 146 17 10.88.226.1 192.168.202.22 2678 443 Gi0/0 Gi0/1 8567 6 10.89.16.226 192.168.150.60 3562 80 Gi0/0 Gi0/1 4012 6To view only the SNMP on UDP port 161, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_161_.*_17 command to display the related NetFlow records.
For more information about Cisco IOS Flexible NetFlow, refer to Flexible NetFlow Configuration Guide, Cisco IOS Release 15.1M&T and Cisco IOS Flexible NetFlow Configuration Guide, Release 12.4T.
Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls
Mitigation: Application Layer Protocol Inspection
Application layer protocol inspection is available beginning in software release 7.2(1) for the Cisco ASA 5500 Series Adaptive Security Appliance, software release 8.5 for the Cisco Catalyst 6500 Series ASA Services Module, and in software release 4.0(1) for the Cisco Firewall Services Module. This advanced security feature performs deep packet inspection of traffic that transits the firewall. Administrators may construct an inspection policy for applications that require special handling through the configuration of inspection class maps and inspection policy maps, which are applied by means of a global or interface service policy.
Additional information about application layer protocol inspection is in the Configuring Application Layer Protocol Inspection section of the Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2 and the Configuring Application Inspection section of the Cisco Catalyst 6500 Series ASA Services Module CLI Configuration Guide, 8.5.
Caution: Application layer protocol inspection will decrease firewall performance. Administrators are advised to test performance impact in a lab environment before this feature is deployed in production environments.Simple Network Management Protocol Application Inspection
Using the Simple Network Management Protocol (SNMP) application inspection engine on the Cisco ASA 5500 Series Adaptive Security Appliances and the Cisco Firewall Services Modules, administrators can configure a policy that prevents SNMPv3 messages while allowing SNMPv1, SNMPv2, and SNMPv2c messages to transit the firewall. The following SNMP application inspection uses the Modular Policy Framework (MPF) to create a policy for inspection of traffic on UDP port 161. The SNMP inspection policy will drop SNMPv3 connections.! !-- Configure an SNMP map to deny SNMPv3 connections ! snmp-map deny_SNMPv3 deny version 3 ! !-- Add the above-configured SNMP map to the default policy !-- "global_policy" and default class "inspection_default" !-- and use it to inspect SNMP traffic that transits the firewall ! policy-map global_policy class inspection_default inspect snmp deny_SNMPv3 ! !-- By default, the policy "global_policy" is applied globally, !-- which results in the inspection of traffic that enters the !-- firewall from all interfaces ! service-policy global_policy global
Additional information about SNMP application inspection and the MPF is in the SNMP Inspection section of the Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2.Identification: Application Layer Protocol Inspection
Firewall syslog message 416001 will be generated when a Simple Network Management Protocol (SNMP) packet is dropped. The syslog message will identify the SNMP version of the dropped packet. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 416001.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog on the Cisco FWSM for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers is in Monitoring the Firewall Services Module.
In the following example, the show logging | grep regex command extracts syslog messages from the logging buffer on the firewall. These messages provide additional information about denied packets that could indicate attempts to exploit this vulnerability. Administrators can use different regular expressions with the grep keyword to search for specific data in the logged messages.Simple Network Management Protocol Application Inspection
firewall# show logging | grep 416001 May 30 2013 22:03:49: %ASA-4-416001: Dropped UDP SNMP packet from outside:192.168.60.63/32769 to inside:192.168.60.42/161; version (3) is not allowed thru the firewall May 30 2032 22:03:50: %ASA-4-416001: Dropped UDP SNMP packet from outside:192.168.60.63/32769 to inside:192.168.60.42/161; version (3) is not allowed thru the firewall May 30 2013 22:03:51: %ASA-4-416001: Dropped UDP SNMP packet from outside:192.168.60.63/32769 to inside:192.168.60.42/161; version (3) is not allowed thru the firewall May 30 2013 22:03:52: %ASA-4-416001: Dropped UDP SNMP packet from outside:192.168.60.63/32769 to inside:192.168.60.42/161; version (3) is not allowed thru the firewall
With SNMP inspection enabled, the show service-policy command will identify the number of SNMP packets inspected and dropped by this feature. The following example shows output for show service-policy:firewall# show service-policy | include snmp Inspect: snmp deny_SNMPv3, packet 236, drop 6, reset-drop 0 firewall#
In the preceding example, 236 SNMP packets have been inspected and 6 SNMP packets have been dropped.
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THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
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Show LessVersion Description Section Date 2 Cisco has clarified that there is no associated mitigation information available for CVE-2013-3633 in their Applied Mitigation Bulletin: Identifying and Mitigating the Siemens SCALANCE Privilege Escalation Vulnerabilities. 2013-June-04 20:42 GMT 1 Cisco Applied Mitigation Bulletin initial public release 2013-June-03 19:37 GMT 1 Alert History
Initial Release2013-June-03 19:37 GMT
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The security vulnerability applies to the following combinations of products.
Primary Products Siemens Corp Scalance X Switches Firmware 3.7 (.0, .1, .2, Base) | 4.0 (Base) | 4.1 (Base) | 4.2 (Base) | 4.3 (Base) | 4.4 (Base) | 4.5 (Base) | 5.0 (Base)
Associated Products
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THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE ALERTS AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy and may lack important information or contain factual errors. The information in this document is intended for end users of Cisco products