Cisco Response

• This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Cisco IOS Software Common Industrial Protocol Vulnerabilities and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
  
  This document provides identification and mitigation techniques that administrators can deploy on Cisco network devices. The techniques presented in this document only apply to the Cisco IOS Software UDP CIP Denial of Service Vulnerability.

Vulnerability Characteristics

• Cisco IOS Software contains a vulnerability when it processes crafted Common Industrial Protocol (CIP) IP version 4 (IPv4) 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. The attack vector for exploitation is through IPv4 packets using UDP ports 2222 or 44818. An attacker could exploit this vulnerability using spoofed packets.
  
  This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2015-0647.

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-cip.

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 the following methods:
  

  • Infrastructure access control lists (iACLs)
  • Unicast Reverse Path Forwarding (uRPF)
  • IP source guard (IPSG)

  
  These protection mechanisms filter and drop, as well as verify the source IP address of, packets that are attempting to exploit this vulnerability.
  
  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)
  • uRPF

  
  These protection mechanisms filter and drop, as well as verify the source IP address of, packets that are attempting to exploit this vulnerability.
  
  Cisco IOS NetFlow and Flexible NetFlow records can provide visibility into network-based exploitation attempts.
  
  Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit this vulnerability.

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

• 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: Infrastructure Access Control Lists

  To protect infrastructure devices and minimize the risk, impact, and effectiveness of direct infrastructure attacks, administrators are advised to deploy iACLs to perform policy enforcement of traffic sent to infrastructure equipment. Administrators can construct an iACL by explicitly permitting only authorized traffic sent to infrastructure devices in accordance with existing security policies and configurations. For the maximum protection of infrastructure devices, deployed iACLs should be applied in the ingress direction on all interfaces to which an IP address has been configured. An iACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.

  The iACL policy denies unauthorized IPv4 packets on UDP port 2222 and 44818 that are sent to affected devices. In the following example, 192.168.60.0/24 and represents the IP address space that is used by the affected devices, and the hosts at 192.168.100.1 and 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. Whenever possible, infrastructure address space should be distinct from the address space used for user and services segments. Using this addressing methodology will assist with the construction and deployment of iACLs.

  For additional information about iACLs, see Protecting Your Core: Infrastructure Protection Access Control Lists.

  
  ip access-list extended Infrastructure-ACL-Policy 
    !
    !-- Include explicit permit statements for trusted sources that
    !-- require access on the vulnerable UDP ports
    !
    permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 2222
    permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 44818
    !
    !-- The following vulnerability-specific access control entries
    !-- (ACEs) can aid in identification of attacks
    !
    deny udp any 192.168.60.0 0.0.0.255 eq 2222
    deny udp any 192.168.60.0 0.0.0.255 eq 44818
    !
    !-- 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
    !
    deny ip any 192.168.60.0 0.0.0.255
    !  !
    !
    !-- Apply tACL to interface in the ingress direction
    !
  interface GigabitEthernet0/0
   ip access-group Infrastructure-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 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 .

  For information about how to use the Cisco IOS Software command line interface to gauge the effectiveness of the iACL, see the Cisco Security Intelligence Operations white paper Identifying the Effectiveness of Security Mitigations Using Cisco IOS Software.

  Mitigation: Spoofing Protection

  Unicast Reverse Path Forwarding

  The vulnerability that is 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 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 that is described in this document.

  Additional information about the deployment and configuration of IPSG is in Configuring DHCP Features and IP Source Guard.

  
  

  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 packets on UDP ports 2222 and 44818 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 hosts at 192.168.100.1 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 ports
    !
    access-list tACL-Policy extended permit udp host 192.168.100.1 
       192.168.60.0 0.0.0.255 eq 2222
    access-list tACL-Policy extended permit udp host 192.168.100.1 
       192.168.60.0 0.0.0.255 eq 44818
    !
    !-- The following vulnerability-specific access control entries
    !-- (ACEs) can aid in identification of attacks
    !
    access-list tACL-Policy extended deny udp any 192.168.60.0 255.255.255.0 eq 2222
    access-list tACL-Policy extended deny udp any 192.168.60.0 255.255.255.0 eq 44818
    !
    !-- 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
    !  !
    !
    !-- Apply tACL to interfaces in the ingress direction
    !
    access-group 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.

  Mitigation: Spoofing Protection Using Unicast Reverse Path Forwarding

  The vulnerability that is 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 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 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 identifiers and the respective Cisco IPS signatures that will trigger events on potential attempts to exploit this vulnerability.

  CVE ID	Signature Release	Signature ID	Signature Name	Enabled	Severity	Fidelity*
  CVE-2015-0647	S858	5032-0	Cisco IOS Software Common Industrial Protocol Denial of Service	Yes	High	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.

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 Portal
  • 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 Firewall Products - Home Page on Cisco.com
  • Cisco Catalyst 6500 Series ASA Services Module
  • Cisco 5500-X
  • Cisco ASA-CX
  • Unicast Reverse Path Forwarding Enhancements for the Internet Service Provider
  • Cisco Intrusion Prevention System
  • Cisco IPS Signature Downloads
  • Cisco IPS Signature Search Page
  • 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	12.2EX (12.2(44)EX, 12.2(44)EX1) | 12.2IRD (12.2(33)IRD1) | 12.2IRE (12.2(33)IRE3) | 12.2SE (12.2(46)SE, 12.2(46)SE1, 12.2(46)SE2, 12.2(50)SE, 12.2(50)SE1, 12.2(50)SE2, 12.2(50)SE3, 12.2(50)SE4, 12.2(50)SE5, 12.2(52)SE, 12.2(52)SE1, 12.2(55)SE, 12.2(55)SE3, 12.2(55)SE4, 12.2(55)SE5, 12.2(55)SE6, 12.2(55)SE7, 12.2(55)SE8, 12.2(55)SE9, 12.2(58)SE2) | 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) | 15.0EB (15.0(2)EB) | 15.0ED (15.0(2)ED1) | 15.0EY (15.0(1)EY, 15.0(1)EY1, 15.0(1)EY2, 15.0(2)EY, 15.0(2)EY1, 15.0(2)EY2, 15.0(2)EY3) | 15.0SE (15.0(2)SE, 15.0(2)SE1, 15.0(2)SE10, 15.0(2)SE2, 15.0(2)SE3, 15.0(2)SE4, 15.0(2)SE5, 15.0(2)SE6, 15.0(2)SE7, 15.0(2a)SE6) | 15.2E (15.2(2)E, 15.2(2)E1, 15.2(2b)E) | 15.2EY (15.2(1)EY, 15.2(1)EY1, 15.2(1)EY2) | 15.2JAZ (15.2(4)JAZ) | 15.2JB (15.2(2)JB1) | 15.3JA (15.3(3)JA, 15.3(3)JA1, 15.3(3)JA1m, 15.3(3)JA1n, 15.3(3)JA100, 15.3(3)JA2, 15.3(3)JA75) | 15.3JAA (15.3(3)JAA) | 15.3JAB (15.3(3)JAB, 15.3(3)JAB1) | 15.3JN (15.3(3)JN) | 15.3JNB (15.3(3)JNB) | 15.3S (15.3(2)S2)

  
  
  

  Associated Products