Cisco Applied Mitigation Bulletin-
Cisco Response
This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Cisco IOS Software Session Initiation Protocol Denial of Service Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
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Repeated attempts to exploit this vulnerability could result in a sustained DoS condition.
The attack vectors for exploitation are through IPv4 and IPv6 packets using the following protocols and ports:- SIP using TCP port 5060
- SIP using TCP port 5061
- SIP using UDP port 5060
This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2014-2106.
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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-20140326-sip.
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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:- Transit access control lists (tACLs)
- Unicast Reverse Path Forwarding (Unicast RPF)
- IP source guard (IPSG)
The proper deployment and configuration of Unicast RPF 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 spoofing attacks at the access layer.
Effective means of exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance and the Firewall Services Module (FWSM) for Cisco Catalyst 6500.- tACLs
- Unicast RPF
Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit this vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.
Cisco IOS Software, Cisco ASA, and 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 ASA, Cisco ASASM, and Cisco FWSM Firewalls
- Sourcefire 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 this vulnerability when the attack originates from a trusted source address. The tACL policy denies unauthorized IPv4 and IPv6 packets on and that are sent to affected devices. In the following example, 192.168.60.0/242001: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 TCP and UDP ports ! ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! ! !-- 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 TCP and UDP ports ! ! !-- The following vulnerability-specific ACEs can !-- aid in identification of attacks to global and !-- link-local addresses ! ! !-- 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.
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 TCP ports 5060 and 5061 and UDP port 5060 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.
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 TCP and UDP ports ! access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 access-list tACL-Policy extended permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! access-list tACL-Policy extended deny tcp any 192.168.60.0 0.0.0.255 eq 5060 access-list tACL-Policy extended deny tcp any 192.168.60.0 0.0.0.255 eq 5061 access-list tACL-Policy extended deny udp any 192.168.60.0 0.0.0.255 eq 5060 ! !-- 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 0.0.0.255 ! ! !-- Create the corresponding IPv6 tACL ! ! !-- Include explicit permit statements for trusted sources that !-- require access on the vulnerable TCP and UDP ports ! ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060 ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5061 ipv6 access-list IPv6-tACL-Policy permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 5060 ! !-- The following vulnerability-specific ACEs can !-- aid in identification of attacks ! ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:DB8:1:60::/64 eq 5060 ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:DB8:1:60::/64 eq 5061 ipv6 access-list IPv6-tACL-Policy deny udp any 2001:DB8:1:60::/64 eq 5060 ! !-- 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 one unified ACL.
For more information about unified ACLs, refer to the Adding an Extended Access List section of the Cisco ASA configuration guide.
Sourcefire Signature Information
The following Sourcefire signatures are available for the Cisco IOS Software Session Initiation Protocol denial of service vulnerability.
Signature Description Applicable Rule DOS Cisco IOS SIP header denial of service attempt 1:30282 DOS Cisco IOS SIP header denial of service attempt 1:30283
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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 Sourcefire IPS signature information is available. 2014-March-27 17:14 GMT 1 Cisco Applied Mitigation Bulletin initial public release. 2014-March-26 17:12 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 15.3M (15.3(3)M, 15.3(3)M1) | 15.3S (15.3(3)S, 15.3(3)S1) | 15.3XB (15.3(3)XB12) Cisco IOS XE Software 3.10S (3.10.0S, 3.10.1S, 3.10.1xbS)
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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