Cisco Applied Mitigation Bulletin-
This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Multiple Vulnerabilities in Cisco IOS Software Multicast Domain Name System and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
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Cisco IOS Software mDNS Gateway Memory Leak Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability could lead to a memory leak resulting in an interface wedge condition and cause the affected device to reload. The attack vector for exploitation is through mDNS IPv4 and IPv6 packets using UDP port 5353. An attacker could exploit this vulnerability using spoofed packets.
This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2014-3357.
Cisco IOS Software mDNS Gateway DOS Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability could cause the affected device to crash and result in a denial of service (DoS) condition. The attack vector for exploitation is through mDNS IPv4 and IPv6 packets using UDP port 5353. An attacker could exploit this vulnerability using spoofed packets.
This vulnerability has been assigned CVE ID CVE-2014-3358.
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Information about vulnerable, unaffected, and fixed software is available in the Cisco Security Advisory, which is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20140924-mdns
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Cisco devices provide several countermeasures for these vulnerabilities. Administrators are advised to consider these protection methods to be general security best practices for infrastructure devices and the traffic that transits the network. This section of the document provides an overview of these techniques.
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)
- IOS NetFlow and Flexible NetFlow
The proper deployment and configuration of uRPF provides an effective means of protection against attacks that use packets with spoofed source IP addresses. uRPF 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 spoofing attacks at the access layer.
Effective means of exploit prevention can also be provided by the Cisco ASA 5500 and 5500-X 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 the following:- Transit access control lists (tACLs)
- Unicast Reverse Path Forwarding (uRPF)
Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit these vulnerabilities.
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Organizations are advised to follow their standard risk evaluation and mitigation processes to determine the potential impact of these vulnerabilities. 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 ASA, Cisco ASASM, and Cisco FWSM Firewalls
- Cisco Intrusion Prevention System
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 these vulnerabilities when the attack originates from a trusted source address.
The tACL policy denies unauthorized IPv4 and IPv6 packets on UDP port 5353 that are sent to affected devices. In the following example, 224.0.0.251 and FF02::FB represent the multicast address space that is used by 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 in Transit Access Control Lists: Filtering at Your Edge.! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable UDP port ! access-list 150 permit udp host 192.168.100.1 host 224.0.0.251 eq 5353 ! !-- The following vulnerability-specific access control entry !-- (ACE) can aid in identification of attacks ! access-list 150 deny udp any host 224.0.0.251 eq 5353 ! !-- 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 ! ! !-- Create the corresponding IPv6 tACL ! ipv6 access-list IPv6-Transit-ACL-Policy ! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable UDP port ! permit udp host 2001:DB8::100:1 host FF02::FB eq 5353 ! !-- The following vulnerability-specific ACE can !-- aid in identification of attacks to global and !-- link-local addresses ! deny udp any host FF02::FB eq 5353 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in !-- accordance with existing security policies and configurations !-- and allow IPv6 neighbor discovery packets, which !-- include neighbor solicitation packets and neighbor !-- advertisement packets ! permit icmp any any nd-ns permit icmp any any nd-na ! !-- Explicit deny for all other IPv6 traffic ! deny ipv6 any any ! ! !-- Apply tACLs to interface in the ingress direction ! interface GigabitEthernet0/0 ip access-group 150 in ipv6 traffic-filter IPv6-Transit-ACL-Policy 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 commands no ip unreachables and no ipv6 unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration commands ip icmp rate-limit unreachable interval-in-ms and ipv6 icmp error-interval interval-in-ms.
For information about how to use the Cisco IOS command-line interface to gauge the effectiveness of the tACL, see the Cisco Security Intelligence Operations white paper Identifying the Effectiveness of Security Mitigations Using Cisco IOS Software.
Unicast Reverse Path Forwarding
The vulnerabilities that are 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.
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 GuardIP 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 vulnerabilities that are described in this document.
Additional information about the deployment and configuration of IPSG is in Configuring DHCP Features and IP Source Guard.
Identification: IPv4 and IPv6 Traffic Flow Identification Using Cisco IOS NetFlow
Administrators can configure Cisco IOS NetFlow and Cisco IOS Flexible NetFlow on Cisco IOS routers and switches to aid in the identification of IPv4 and IPv6 traffic flows that may be attempts to exploit these vulnerabilities. Administrators are advised to investigate flows to determine whether they are attempts to exploit these vulnerabilities or whether they are legitimate traffic flows. Administrators can also configure filters to highlight traffic on individual ports to identify traffic flows that may be attempts to exploit the vulnerabilities mentioned in this document. For additional information, see the Cisco IOS NetFlow and Cisco IOS Flexible NetFlow section of the paper Identifying the Effectiveness of Security Mitigations Using Cisco IOS Software.Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls
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 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 these vulnerabilities when the attack originates from a trusted source address.
The tACL policy denies unauthorized IPv4 and IPv6 packets on UDP port 5353 that are sent to affected devices. In the following example, 224.0.0.251 and FF02::FB represent the multicast address space that is used by the affected devices, and the hosts at 192.168.100.1 and 2001:DB8::100:1 are considered trusted sources that require access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.
For additional information about tACLs, see Transit Access Control Lists: Filtering at Your Edge.
! !-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable UDP port ! access-list tACL-Policy extended permit udp host 192.168.100.1 host 224.0.0.251 eq 5353 ! !-- The following vulnerability-specific access control entry !-- (ACE) can aid in identification of attacks ! access-list tACL-Policy extended deny udp any host 224.0.0.251 eq 5353 ! !-- 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 tACL-Policy extended deny ip any host 224.0.0.251 eq 5353 ! ! !-- Create the corresponding IPv6 tACL ! ! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable UDP port ! ipv6 access-list IPv6-tACL-Policy permit udp host 2001:DB8::100:1 host FF02::FB ! !-- The following vulnerability-specific ACE can !-- aid in identification of attacks ! ipv6 access-list IPv6-tACL-Policy deny udp any host FF02::FB eq 5353 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in !-- accordance with existing security policies and configurations ! ! !-- Explicit deny for all other IPv6 traffic ! ipv6 access-list IPv6-tACL-Policy deny ip any any ! ! !-- Apply tACLs to interfaces in the ingress direction ! access-group tACL-Policy in interface outside access-group IPv6-tACL-Policy in interface outside
For information about using the Cisco firewall command-line interface to gauge the effectiveness of tACLs, see the Cisco Security Intelligence Operations white paper Identification of Security Exploits with Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls.
Starting in Cisco ASA Software Release 9.0, ACLs (namely unified ACLs) support IPv4 and IPv6 addresses. A mix of IPv4 and IPv6 addresses can be specified for the source and destination of the ACL. The any4 and any6 keywords were added to represent IPv4-only and IPv6-only traffic, respectively.
The IPv4 and IPv6 access list entries (ACEs) presented in the IPv4 and IPv6 ACLs of this section could also be incorporated in one unified ACL.
For additional information about unified ACLs, see the Adding an Extended Access List section of the Cisco ASA configuration guide.
Mitigation: Spoofing Protection Using Unicast Reverse Path Forwarding
The vulnerabilities that are described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure 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. In an enterprise environment, uRPF may be enabled at the Internet edge and at the internal access layer on the user-supporting Layer 3 interfaces.
For additional information about the configuration and use of uRPF, reference the Cisco Security Appliance Command Reference for ip verify reverse-path and the Understanding Unicast Reverse Path Forwarding Cisco Security Intelligence Operations white paper.
For information on how to use the firewall command line interface to gauge the effectiveness of spoofing protection, please refer to the Cisco Security Intelligence Operations white paper Identification of Security Exploits with Cisco ASA, Cisco ASASM, and Cisco FWSM Firewalls.
Cisco Intrusion Prevention System
Mitigation: Cisco IPS Signature Table
Administrators can use the Cisco IPS appliances and services modules to provide threat detection and help prevent attempts to exploit the vulnerability described in this document. The following table provides an overview of CVE identifier and the respective Cisco IPS signature that will trigger events on potential attempts to exploit this vulnerability.
CVE ID Signature Release Signature ID Signature Name Enabled Severity Fidelity* CVE-2014-3357 S823 4565-0 Malformed mDNS Response Yes Medium 85 * Fidelity is also referred to as Signature Fidelity Rating (SFR) and is the relative measure of the accuracy of the signature (predefined). The value ranges from 0 through 100 and is set by Cisco Systems, Inc.
Administrators can configure Cisco IPS sensors to perform an event action when an attack is detected. The configured event action performs preventive or deterrent controls to help protect against an attack that is attempting to exploit the vulnerability listed in the preceding table.
Exploits that use spoofed IP addresses may cause a configured event action to inadvertently deny traffic from trusted sources.
Cisco IPS sensors are most effective when deployed in inline protection mode combined with the use of an event action. Automatic Threat Prevention for Cisco IPS 7.x and 6.x sensors that are deployed in inline protection mode provides threat prevention against an attack that is attempting to exploit the vulnerability that is described in this document. Threat prevention is achieved through a default override that performs an event action for triggered signatures with a riskRatingValue greater than 90.
For additional information about the risk rating and threat rating calculation, reference Risk Rating and Threat Rating: Simplify IPS Policy Management.
For information on using Cisco Security Manager to view the activity from a Cisco IPS sensor, see Identification of Malicious Traffic Using Cisco Security Manager white paper.
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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 1 Initial Release
2014-September-24 16:02 GMT
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Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at https://sec.cloudapps.cisco.com/security/center/resources/security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.
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The security vulnerability applies to the following combinations of products.
Primary Products Cisco IOS 15.1SY (15.1(2)SY, 15.1(2)SY1) | 15.2E (15.2(1)E, 15.2(1)E1) | 15.4S (15.4(1)S) | 15.4T (15.4(1)T, 15.4(1)T1) Cisco IOS XE Software 2.1 (2.1.0, 2.1.1, 2.1.2) | 2.2 (2.2.1, 2.2.2) | 2.3 (2.3.0, 2.3.0t, 2.3.1t, 2.3.2) | 2.4 (2.4.1) | 2.5 (2.5.0) | 2.6 (2.6.0, 2.6.1, 2.6.2) | 3.1S (3.1.0S, 3.1.1S, 3.1.2S, 3.1.3S) | 3.2S (3.2.0S, 3.2.1S, 3.2.2S) | 3.3S (3.3.0S, 3.3.1S, 3.3.2S) | 3.3SE (3.3.0SE, 3.3.1SE) | 3.4S (3.4.0S, 3.4.1S, 3.4.2S, 3.4.3S, 3.4.4S, 3.4.5S, 3.4.6S) | 3.4SG (3.4.0SG, 3.4.1SG, 3.4.2SG) | 3.5E (3.5.0E) | 3.5S (Base, 3.5.0S, 3.5.1S, 3.5.2S) | 3.6S (Base, 3.6.0S, 3.6.1S, 3.6.2S) | 3.7S (Base, 3.7.0S, 3.7.1S, 3.7.2S, 3.7.3S, 3.7.4S) | 3.8S (Base, 3.8.0S, 3.8.1S) | 3.9S (3.9.0S, 3.9.1S) | 3.10S (3.10.0aS) | 3.11S (3.11.0S)
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.
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