Cisco Response

• This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Cisco IOS Software and IOS XE Software mDNS Gateway Denial of Service Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

• The Cisco mDNS Gateway exhibits a vulnerability when processing IP version 4 (IPv4) and IP version 6 (IPv6) packets. This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability could result in a denial of service (DoS) condition. Repeated attempts to exploit this vulnerability could result in a sustained DoS condition. The attack vector for exploitation is through SIP 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) identifier CVE-2015-0650.

Vulnerability Overview

• Vulnerability Overview

  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-20150325-mdns.

Mitigation Technique Overview

• Mitigation Technique Overview

  Cisco devices provide several countermeasures for this vulnerability 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 transit access control lists (tACL). This protection mechanism filters and drops packets that are attempting to exploit this vulnerability

  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 transit access control lists (tACL). This protection mechanism filters and drops packets that are attempting to exploit this vulnerability.

Risk Management

• Risk Management

  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.

Device-Specific Mitigation and Identification

• Device-Specific Mitigation and Identification

  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 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 IPv4 and IPv6 packets on UDP port 5353 that are sent to affected devices. In the following example, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP 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 192.168.60.0 0.0.0.255 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 2001:DB8:1:60::/64 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 white 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 this vulnerability 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, 192.168.60.0/24 and 2001:DB8:1:60::/64 represent the IP 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 192.168.60.0 255.255.255.0 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 192.168.60.0 255.255.255.0
    !
  !
  !-- 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 eq 5353
    !
    !-- The following vulnerability-specific ACE can
    !-- aid in identification of attacks
    !
    ipv6 access-list IPv6-tACL-Policy deny udp any 2001:DB8:1:60::/64 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.

Additional Information

• 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.

Revision History

• Version	Description	Section	Date
  1	Initial Release		2015-March-25 16:01 GMT

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Cisco Security Procedures

• 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.

Related Information

• • Cisco Applied Mitigation Bulletins
  • Cisco Security
  • Cisco Security IntelliShield Alert Manager Service
  • Cisco Guide to Harden Cisco IOS Devices
  • Understanding Cross-Site Scripting (XSS) Threat Vectors
  • Cisco IOS NetFlow - Home Page on Cisco.com
  • Cisco IOS NetFlow White Papers
  • NetFlow Performance Analysis
  • Cisco Network Foundation Protection White Papers
  • Cisco Network Foundation Protection Presentations
  • TTL Expiry Attack Identification and Mitigation
  • A Security-Oriented Approach to IP Addressing
  • Countermeasures for the Malicious Use of IPv6 Type 0 Routing Headers
  • Understanding Control Plane Protection
  • Zone-Based Policy Firewall Design and Application Guide
  • Securing Tool Command Language on Cisco IOS
  • Cisco Firewall Products - Home Page on Cisco.com
  • Cisco Catalyst 6500 Series ASA Services Module
  • Cisco 5500-X
  • Cisco ASA-CX
  • Configuring the Identity Firewall
  • Configuring the Botnet Traffic Filter
  • User Guide for ASA CX and Cisco Prime Security Manager
  • Cisco ACE Application Control Engine Module Documentation
  • Unicast Reverse Path Forwarding Enhancements for the Internet Service Provider
  • Cisco Intrusion Prevention System
  • Cisco IPS Signature Downloads
  • Sourcefire Next-Generation Security
  • Sourcefire IPS Snort Rules
  • Cisco IPS Signature Search Page
  • Cisco Security Manager
  • Cisco Web Security Appliance (PDF)
  • Cisco Email Security Appliance (PDF)
  • Cisco Cloud Web Security Guide
  • Common Vulnerabilities and Exposures (CVE)
  • Subscribe to Cisco Applied Mitigation Bulletins

Affected Products

• The security vulnerability applies to the following combinations of products.
  
  

  Primary Products
  Cisco	IOS	12.2IRD (12.2(33)IRD1) | 12.2IRE (12.2(33)IRE3) | 12.2SQ (12.2(44)SQ1) | 12.2SXI (12.2(33)SXI4b) | 12.4JAM (12.4(25e)JAM1) | 12.4JAP (12.4(25e)JAP1m) | 12.4JAZ (12.4(25e)JAZ1) | 15.0ED (15.0(2)ED1) | 15.1SY (15.1(2)SY, 15.1(2)SY1, 15.1(2)SY2, 15.1(2)SY3) | 15.2E (15.2(1)E, 15.2(1)E1, 15.2(1)E2, 15.2(1)E3, 15.2(2)E) | 15.2JB (15.2(2)JB1) | 15.3JA (15.3(3)JA1n) | 15.3JAB (15.3(3)JAB1) | 15.3JN (15.3(3)JN) | 15.3JNB (15.3(3)JNB) | 15.3S (15.3(2)S2, 15.3(3)S, 15.3(3)S1, 15.3(3)S1a, 15.3(3)S2, 15.3(3)S2a, 15.3(3)S3) | 15.4M (15.4(3)M, 15.4(3)M1, 15.4(3)M2) | 15.4S (15.4(1)S, 15.4(1)S1, 15.4(1)S2, 15.4(2)S, 15.4(2)S1, 15.4(3)S) | 15.4SN (15.4(2)SN, 15.4(2)SN1, 15.4(3)SN, 15.4(3)SN1) | 15.4T (15.4(1)T, 15.4(1)T1, 15.4(1)T2, 15.4(2)T, 15.4(2)T1)
  	Cisco IOS XE Software	3.3SE (3.3.0SE, 3.3.1SE) | 3.5E (3.5.0E, 3.5.1E, 3.5.2E, 3.5.3E) | 3.6E (3.6.0E) | 3.10S (3.10.0S, 3.10.0aS, 3.10.1S, 3.10.1xbS, 3.10.1xcS, 3.10.2S, 3.10.2aS, 3.10.3S) | 3.11S (3.11.0S, 3.11.1S, 3.11.2S) | 3.12S (3.12.0S, 3.12.1S) | 3.13S (3.13.0S, 3.13.0aS)

  
  
  

  Associated Products