This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Multiple Vulnerabilities in Cisco Unified Communications Manager and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
There are multiple vulnerabilities in Cisco Unified Communications Manager. The following subsections summarize these vulnerabilities:
Session Initiation Protocol (SIP) Denial of Service Vulnerabilities: These vulnerabilities can be exploited remotely without authentication and without end-user interaction. Successful exploitation of these vulnerabilities may result in a denial of service (DoS) condition.
The attack vectors for exploitation are through packets using the following protocols and ports:
An attacker could exploit these vulnerabilities using spoofed packets.
These vulnerabilities have been assigned CVE identifiers CVE-2011-1604, CVE-2011-1605, and CVE-2011-1606.
Cisco Unified Reporting Unauthorized File Upload Vulnerability: This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may allow a remote attacker to upload a malicious file. The attack vector for exploitation is through HTTPS packets using TCP port 8443.
This vulnerability has been assigned CVE identifier CVE-2011-1607.
Multiple SQL Injection Vulnerabilities: These vulnerabilities can be exploited remotely with and without authentication, and without end-user interaction. Successful exploitation of these vulnerabilities may allow information disclosure, which enables an attacker to learn information about the affected device.
The attack vectors for exploitation are through packets using the following protocols and ports:
These vulnerabilities have been assigned CVE identifiers CVE-2011-1609 and CVE-2011-1610.
Information about vulnerable, unaffected, and fixed software is available in the PSIRT Security Advisory, which is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20110427-cucm.
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:
These protection mechanisms filter and drop, as well as verify the source IP address of, packets that are attempting to exploit these vulnerabilities.
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.
These protection mechanisms filter and drop, as well as verify the source IP address of, packets that are attempting to exploit these vulnerabilities.
Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit these vulnerabilities.
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.
The Cisco Security Monitoring, Analysis, and Response System (Cisco Security MARS) appliance can also provide visibility through incidents, queries, and event reporting.
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.
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:
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 SIP packets on TCP and UDP ports 5060 and 5061, HTTP packets on TCP ports 80 and 8080 and HTTPS packets on TCP ports 443 and 8443 that are sent to affected devices. In the following example, 192.168.60.0/24 is 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 in Transit Access Control Lists: Filtering at Your Edge.
!-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable ports ! access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 access-list 150 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 access-list 150 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 80 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 8080 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 8443 ! !-- The following vulnerability-specific access control entries !-- (ACEs) can aid in identification of attacks ! access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 access-list 150 deny udp any 192.168.60.0 0.0.0.255 eq 5060 access-list 150 deny udp any 192.168.60.0 0.0.0.255 eq 5061 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 80 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 443 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 8080 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 8443 ! !-- 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 tACL 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.
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 (Unicast RPF) as a protection mechanism against spoofing.
Unicast RPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on Unicast RPF to provide complete spoofing protection because spoofed packets may enter the network through a Unicast RPF-enabled interface if an appropriate return route to the source IP address exists. Administrators are advised to take care to ensure that the appropriate Unicast RPF 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, Unicast RPF might be enabled at the Internet edge and the internal access layer on the user-supporting Layer 3 interfaces.
Additional information is in the Unicast Reverse Path Forwarding Loose Mode Feature Guide.
For additional information about the configuration and use of Unicast RPF, reference the Understanding Unicast Reverse Path Forwarding Applied Intelligence 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 Unicast RPF 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.
After the administrator applies the tACL to an interface, the show ip access-lists command will identify the number of SIP packets on TCP and UDP ports 5060 and 5061, HTTP packets on TCP ports 80 and 8080 and HTTPS packets on TCP ports 443 and 8443 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit these vulnerabilities. Example output for show ip access-lists 150 follows:
router#show ip access-lists 150
Extended IP access list 150
10 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061
30 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060
40 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061
50 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 80
60 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443
70 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 8080
80 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 8443
90 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 (17 matches)
100 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 (19 matches)
110 deny udp any 192.168.60.0 0.0.0.255 eq 5060 (3 matches)
120 deny udp any 192.168.60.0 0.0.0.255 eq 5061 (49 matches)
130 deny tcp any 192.168.60.0 0.0.0.255 eq 80 (32 matches)
140 deny tcp any 192.168.60.0 0.0.0.255 eq 443 (20 matches)
150 deny tcp any 192.168.60.0 0.0.0.255 eq 8080 (35 matches)
160 deny tcp any 192.168.60.0 0.0.0.255 eq 8443 (10 matches)
170 deny ip any any
router#
In the preceding example, access list 150 has dropped the following packets that are received from an untrusted host or network:
For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.
Administrators can use Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Applied Intelligence white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.
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 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 Supervisor Engine 720 or 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 Applied Intelligence white paper.
With Unicast RPF 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 Unicast RPF has dropped.
Note: Beginning with Cisco IOS Software version 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 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 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 cef switching statistics feature
IPv4 CEF input features:
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#
In the preceding show cef drop, show ip cef switching statistics feature and show ip traffic examples, Unicast RPF has dropped 18 IP packets received globally on all interfaces with Unicast RPF configured because of the inability to verify the source address of the IP packets within the Forwarding Information Base of Cisco Express Forwarding.
Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of 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.
router#show ip cache flow
IP packet size distribution (31715553 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.005 .175 .632 .032 .095 .003 .003 .003 .002 .000 .005 .002 .000 .000 .000
512 544 576 1024 1536 2048 2560 3072 3584 4096 4608
.000 .000 .020 .007 .008 .000 .000 .000 .000 .000 .000
IP Flow Switching Cache, 4456704 bytes
24 active, 65512 inactive, 5451612 added
557541771 ager polls, 0 flow alloc failures
Active flows timeout in 2 minutes
Inactive flows timeout in 60 seconds
IP Sub Flow Cache, 533256 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 811 0.0 137 41 0.0 32.3 16.4
TCP-FTP 2108 0.0 6 44 0.0 0.5 22.1
TCP-FTPD 5 0.0 13 52 0.0 0.7 1.5
TCP-WWW 133468 0.0 4 223 0.1 5.5 50.9
TCP-SMTP 32583 0.0 5 60 0.0 28.3 60.0
TCP-other 627608 0.1 12 175 1.8 57.8 24.1
UDP-DNS 284078 0.0 3 63 0.2 15.1 53.5
UDP-NTP 94456 0.0 1 76 0.0 0.3 60.5
UDP-Frag 1 0.0 9 1260 0.0 0.4 60.2
UDP-other 1102669 0.2 8 102 2.1 34.3 47.5
ICMP 1980458 0.4 2 89 1.1 14.3 58.5
IGMP 469264 0.1 2 37 0.2 58.2 41.0
IPINIP 2 0.0 1 76 0.0 0.0 60.4
IPv6INIP 3 0.0 1 863 0.0 0.0 60.4
GRE 2 0.0 1 697 0.0 0.0 60.4
IP-other 724037 0.1 9 89 1.5 95.0 15.6
Total: 5451553 1.2 5 113 7.3 37.5 44.7
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 13C5 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 13C4 5
Gi0/0 192.168.10.17 Gi0/1 192.168.60.97 06 0B89 13C4 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 13C4 1
Gi0/0 10.89.16.226 Gi0/1 192.168.150.60 06 12CA 0016 1
Gi0/0 192.168.120.20 Gi0/1 192.168.60.102 06 0984 1F90 1
Gi0/0 192.168.12.45 Gi0/1 192.168.60.138 06 0911 13C5 3
Gi0/1 192.168.150.41 Gi0/0 192.168.60.24 06 0016 12CA 1
Gi0/0 192.168.12.87 Gi0/1 192.168.60.28 06 0B3E 0050 5
Gi0/0 192.168.10.12 Gi0/1 192.168.60.97 06 0B89 01BB 1
Gi0/0 10.88.226.8 Gi0/1 192.168.202.22 11 007B 007B 1
Gi0/0 192.168.12.15 Gi0/1 192.168.60.209 06 0BD7 20FB 1
Gi0/0 10.89.16.216 Gi0/1 192.168.150.8 06 12CA 0016 1
router#
In the preceding example, there are multiple flows for SIP on TCP ports 5060 (hex value 13C4) and 5061 (hex value 13C5) and UDP ports 5060 (hex value 13C4) and 5061 (hex value13C5) and HTTP on TCP ports 80 (hex value 0050) and 8080 (hex vlaue 1F90) and HTTPS on TCP ports 443 (hex value 01BB) and 8443 (hex halue 20FB).
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 these vulnerabilities. Administrators are advised to compare these flows to baseline utilization for SIP traffic sent on UDP port 5060 and port 5061 and also investigate the flows to determine whether they are sourced from untrusted hosts or networks.
To view only the traffic flows for SIP packets on UDP ports 5060 (hex value 13C4) and 5061 (hex value 13C5), the command show ip cache flow | include SrcIf|_11_.*(13C4|13C5) will display the related UDP NetFlow records as shown here:
UDP Flows
router#show ip cache flow | include SrcIf|_11_.*(13C4|13C5) SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.12.110 Gi0/1 192.168.60.163 11 092A 13C4 6 Gi0/0 192.168.11.230 Gi0/1 192.168.60.20 11 0C09 13C4 1 Gi0/0 192.168.11.131 Gi0/1 192.168.60.245 11 0B66 13C5 18 Gi0/0 192.168.13.7 Gi0/1 192.168.60.162 11 0914 13C4 1 router#
To view only the traffic flows for SIP packets on TCP ports 5060 (hex value 13C4) and 5061 (hex value 13C5) and HTTP packets on TCP ports 80 (hex value 0050) and 8080 (hex value 1F90) and HTTPS packets on TCP ports 443 (hex value 01BB) and 8443 (hex value 20FB), the command show ip cache flow | include SrcIf|_06_.*(13C4|13C5|0050|01BB|1F90|20FB) will display the related TCP NetFlow records as shown here:
TCP Flows
router#show ip cache flow | include SrcIf|_06_.*(13C4|13C5|0050|01BB|1F90|20FB) SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.12.110 Gi0/1 192.168.60.163 06 092A 13C5 6 Gi0/0 192.168.11.230 Gi0/1 192.168.60.20 06 0C09 0050 1 Gi0/0 192.168.11.131 Gi0/1 192.168.60.245 06 0B66 01BB 18 Gi0/0 192.168.13.7 Gi0/1 192.168.60.162 06 0914 0050 7 Gi0/0 192.168.241.106 Gi0/1 192.168.60.27 06 0B7B 13C4 12 Gi0/0 192.168.19.222 Gi0/1 192.168.60.120 06 0C09 20FB 16 Gi0/0 192.168.12.121 Gi0/1 192.168.60.245 06 0B66 01BB 19 Gi0/0 192.168.14.17 Gi0/1 192.168.60.183 06 0914 1F90 9 Gi0/0 192.168.41.86 Gi0/1 192.168.60.217 06 0B7B 20FB 2 router#
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 SIP packets on TCP and UDP ports 5060 and 5061, HTTP packets on TCP ports 80 and 8080 and HTTPS packets on TCP ports 443 and 8443 that are sent to affected devices. In the following example, 192.168.60.0/24 is 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 in Transit Access Control Lists: Filtering at Your Edge.
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable ports
!
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq sip
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 5061
access-list tACL-Policy extended permit udp host 192.168.100.1
192.168.60.0 255.255.255.0 eq sip
access-list tACL-Policy extended permit udp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 5061
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq www
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq https
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 8080
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 8443
!
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks
!
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq sip
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 5061
access-list tACL-Policy extended deny udp any 192.168.60.0 255.255.255.0 eq sip
access-list tACL-Policy extended deny udp any 192.168.60.0 255.255.255.0 eq 5061
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq www
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq https
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 8080
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 8443
!
!-- 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 any
!
!-- Apply tACL to interface(s) in the ingress direction
!
access-group tACL-Policy in interface outside
The vulnerabilities that are described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure Unicast RPF as a protection mechanism against spoofing.
Unicast RPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on Unicast RPF to provide complete spoofing protection because spoofed packets may enter the network through a Unicast RPF-enabled interface if an appropriate return route to the source IP address exists. In an enterprise environment, Unicast RPF might 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 Unicast RPF, reference the Cisco Security Appliance Command Reference for ip verify reverse-path and the Understanding Unicast Reverse Path Forwarding Applied Intelligence white paper.
After the tACL has been applied to an interface, administrators can use the show access-list command to identify the number of SIP packets on TCP and UDP ports 5060 and 5061, HTTP packets on TCP ports 80 and 8080 and HTTPS packets on TCP ports 443 and 8443 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit these vulnerabilities. Example output for show access-list tACL-Policy follows:
firewall#show access-list tACL-Policy access-list tACL-Policy; 17 elements access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq sip access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5061 access-list tACL-Policy line 3 extended permit udp host 192.168.100.1 192.168.60.0 255.255.255.0 eq sip access-list tACL-Policy line 4 extended permit udp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5061 access-list tACL-Policy line 5 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq www access-list tACL-Policy line 6 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq https access-list tACL-Policy line 7 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 8080 access-list tACL-Policy line 8 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 8443 access-list tACL-Policy line 9 extended deny tcp any 192.168.60.0 255.255.255.0 eq sip (hitcnt=30) access-list tACL-Policy line 10 extended deny tcp any 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=43) access-list tACL-Policy line 11 extended deny udp any 192.168.60.0 255.255.255.0 eq sip (hitcnt=70) access-list tACL-Policy line 12 extended deny udp any 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=14) access-list tACL-Policy line 13 extended deny tcp any 192.168.60.0 255.255.255.0 eq www (hitcnt=45) access-list tACL-Policy line 14 extended deny tcp any 192.168.60.0 255.255.255.0 eq https (hitcnt=53) access-list tACL-Policy line 15 extended deny tcp any 192.168.60.0 255.255.255.0 eq 8080 (hitcnt=70) access-list tACL-Policy line 16 extended deny tcp any 192.168.60.0 255.255.255.0 eq 8443 (hitcnt=61) access-list tACL-Policy line 17 extended deny tcp any any
In the preceding example, access list tACL-Policy has dropped the following packets received from an untrusted host or network:
Firewall syslog message 106023 will be generated for packets denied by an access control entry (ACE) that does not have the log keyword present. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 106023.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog on the 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 potential attempts to exploit the vulnerabilities that are described in this document. It is possible to use different regular expressions with the grep keyword to search for specific data in the logged messages.
Additional information about regular expression syntax is in Creating a Regular Expression.
firewall#show logging | grep 106023
Apr 27 2011 00:03:41: %ASA-4-106023: Deny udp src outside:192.0.2.18/16784
dst inside:192.168.60.191/5060 by access-group "tACL-Policy"
Apr 27 2011 00:03:41: %ASA-4-106023: Deny udp src outside:192.0.2.200/16785
dst inside:192.168.60.33/5060 by access-group "tACL-Policy"
Apr 27 2011 00:03:41: %ASA-4-106023: Deny udp src outside:192.0.2.99/16786
dst inside:192.168.60.240/5061 by access-group "tACL-Policy"
Apr 27 2011 00:03:41: %ASA-4-106023: Deny udp src outside:192.0.2.100/16787
dst inside:192.168.60.115/5061 by access-group "tACL-Policy"
Apr 27 2011 00:04:27: %ASA-4-106023: Deny tcp src outside:192.0.2.88/18683
dst inside:192.168.60.38/5060 by access-group "tACL-Policy"
Apr 27 2011 00:04:27: %ASA-4-106023: Deny tcp src outside:192.0.2.175/18684
dst inside:192.168.60.250/5061 by access-group "tACL-Policy"
firewall#
In the preceding example, the messages logged for the tACL tACL-Policy show potentially spoofed SIP packets for TCP and UDP ports 5060 and 5061 sent to the address block assigned to affected devices.
Additional information about syslog messages for ASA security appliances is in Cisco ASA 5500 Series System Log Messages, 8.2. Additional information about syslog messages for the FWSM is in Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Logging System Log Messages.
For additional information about investigating incidents using syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.
Firewall syslog message 106021 will be generated for packets denied by Unicast RPF. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 106021.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog on the 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 potential attempts to exploit the vulnerabilities that are described in this document. It is possible to use different regular expressions with the grep keyword to search for specific data in the logged messages.
Additional information about regular expression syntax is in Creating a Regular Expression.
firewall#show logging | grep 106021
Apr 27 2011 00:03:42: %ASA-1-106021: Deny UDP reverse path check from
192.168.60.1 to 192.168.60.100 on interface outside
Apr 27 2011 00:03:43: %ASA-1-106021: Deny UDP reverse path check from
192.168.60.1 to 192.168.60.100 on interface outside
Apr 27 2011 00:03:43: %ASA-1-106021: Deny TCP reverse path check from
192.168.60.1 to 192.168.60.100 on interface outside
The show asp drop command can also identify the number of packets that the Unicast RPF feature has dropped, as shown in the following example:
firewall#show asp drop frame rpf-violated Reverse-path verify failed 11 firewall#
In the preceding example, Unicast RPF has dropped 11 IP packets received on interfaces with Unicast RPF configured. Absence of output indicates that the Unicast RPF feature on the firewall has not dropped packets.
For additional information about debugging accelerated security path dropped packets or connections, reference the Cisco Security Appliance Command Reference for show asp drop.
Administrators can use Cisco Intrusion Prevention System (IPS) appliances and services modules to provide threat detection and help prevent attempts to exploit some of the vulnerabilities that are described in this document. These vulnerabilities may be detected by the following signatures:
35846-0 - Cisco CUCM Remote Code Execution
Beginning with signature update S562 for sensors running Cisco IPS version 6.x and greater, these vulnerabilities can be detected by signature 35846/0 (Signature Name: Cisco CUCM Remote Code Execution). Signature 35846/0 is enabled by default, triggers a High severity event, has a signature fidelity rating (SFR) of 95, and is configured with a default event action of produce-alert.
Signature 35846/0 fires when a single packet sent using SIP port 5060 is detected. Firing of this signature may indicate a potential exploit of these vulnerabilities.
35866-0 - Cisco CUCM SIP Vulnerability
Beginning with signature update S562 for sensors running Cisco IPS version 6.x and greater, these vulnerabilities can be detected by signature 35866/0 (Signature Name: Cisco CUCM SIP Vulnerability). Signature 35866/0 is enabled by default, triggers a High severity event, has a signature fidelity rating (SFR) of 90, and is configured with a default event action of produce-alert.
Signature 35866/0 fires when a single packet sent using SIP port 5060 is detected. Firing of this signature may indicate a potential exploit of these vulnerabilities.
35085-0 - Cisco Call Manager SQL Injection
Beginning with signature update S562 for sensors running Cisco IPS version 6.x and greater, these vulnerabilities can be detected by signature 35085/0 (Signature Name: Cisco Call Manager SQL Injection). Signature 35085/0 is enabled by default, triggers a High severity event, has a signature fidelity rating (SFR) of 85, and is configured with a default event action of produce-alert.
Signature 35085/0 fires upon detecting a SQL injection attack against Cisco's Call Manager. Firing of this signature may indicate a potential exploit of these vulnerabilities.
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 vulnerabilities that are described in this document.
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 6.x and greater sensors that are deployed in inline protection mode provides threat prevention against an attack that is attempting to exploit the vulnerabilities that are 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.
The Cisco Security Monitoring, Analysis, and Response System (Cisco Security MARS) appliance can create incidents regarding events that are related to the vulnerabilities that are described in this document using IPS signature 35846/0 (Signature Name: Cisco CUCM Remote Code Execution), IPS signature 35866/0 (Signature Name: Cisco CUCM SIP Vulnerability) and IPS signature 35085/0 (Signature Name: Cisco Call Manager SQL Injection). After the S562 dynamic signature update has been downloaded, using keyword NR-35846/0 for IPS signature 35846/0, keyword NR-35866/0 for IPS signature 35866/0 or keyword NR-35085/0 for IPS signature 35085/0 and a query type of All Matching Events on the Cisco Security MARS appliance will provide a report that lists the incidents created by the IPS signature.
Beginning with the 4.3.1 and 5.3.1 releases of Cisco Security MARS appliances, support for the Cisco IPS dynamic signature updates feature has been added. This feature downloads new signatures from Cisco.com or from a local web server, correctly processes and categorizes received events that match those signatures, and includes them in inspection rules and reports. These updates provide event normalization and event group mapping, and they also enable the MARS appliance to parse new signatures from the IPS devices.
Caution: If dynamic signature updates are not configured, events that match these new signatures appear as unknown event type in queries and reports. Because MARS will not include these events in inspection rules, incidents may not be created for potential threats or attacks that occur within the network.
By default, this feature is enabled but requires configuration. If it is not configured, the following Cisco Security MARS rule will be triggered:
System Rule: CS-MARS IPS Signature Update Failure
When this feature is enabled and configured, administrators can determine the current signature version downloaded by MARS by selecting Help > About and reviewing the IPS Signature Version value.
Additional information about dynamic signature updates and instructions for configuring dynamic signature updates are available for the Cisco Security MARS 4.3.1 and 5.3.1 releases.
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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Revision 1.1 |
2011-APRIL-27 |
Updated to include information for IPS signatures and Cisco Security MARS. |
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Revision 1.0 |
2011-APRIL-27 |
Initial public release. |
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.