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Cisco Applied Mitigation Bulletin

Identifying and Mitigating Exploitation of the Cisco Unified Communications Manager Denial of Service Vulnerabilities

Advisory ID: cisco-amb-20100303-cucm

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20100303-cucm

Revision 1.1

For Public Release 2010 March 3 16:00  UTC (GMT)


Contents

Cisco Response
Device-Specific Mitigation and Identification
Additional Information
Revision History
Cisco Security Procedures
Related Information

Cisco Response

This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory Cisco Unified Communications Manager Denial of Service Vulnerabilities and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

There are multiple vulnerabilities in Cisco Unified Communications Manager. The following subsections summarize these vulnerabilities:

Malformed Skinny Call Control Protocol (SCCP) Message 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. Repeated attempts to exploit these vulnerabilities could result in a sustained DoS condition. The attack vector for exploitation is through SCCP packets using TCP ports 2000 and 2443.

These vulnerabilities have been assigned CVE identifiers CVE-2010-0587 and CVE-2010-0588.

Malformed Session Initiation Protocol (SIP) Message 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. Repeated attempts to exploit these vulnerabilities could result in a sustained DoS condition.

The attack vectors for exploitation are through SIP packets using the following protocols and ports:

  • SIP using TCP port 5060
  • SIP using UDP port 5060
  • SIP using TCP port 5061
  • SIP using UDP port 5061

An attacker could exploit the UDP-based vulnerabilities using spoofed packets.

These vulnerabilities have been assigned CVE identifiers CVE-2010-0590 and CVE-2010-0591.

Malformed Computer Telephony Integration (CTI) Manager Message Vulnerability This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may 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 CTI Manager packets using TCP port 2748.

This vulnerability has been assigned CVE identifier CVE-2010-0592.

Information about vulnerable, unaffected, and fixed software is available in the PSIRT Security Advisory, which is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20100303-cucm.

Mitigation Technique Overview

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 (Unicast RPF)
  • 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 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.

Because the potential exists that a trusted networking client could become affected by a worm that does not use packets with spoofed source addresses, Unicast RPF and IPSG do not provide complete protection against these vulnerabilities.

Effective means of exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance, the Cisco PIX 500 Series Security Appliance, and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers using the following:

  • tACLs
  • Unicast RPF

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 Cisco PIX security appliances, 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.

Risk Management

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.

Device-Specific Mitigation and Identification

caution 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

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 SCCP packets on TCP ports 2000 and 2443, SIP packets on TCP ports 5060 and 5061, SIP packets on UDP ports 5060 and 5061, and CTI Manager packets on TCP port 2748 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 2000
access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 2443
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 2748

!
!-- 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 2000
access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 2443
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 2748

!
!-- 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.

Mitigation: Spoofing Protection

Unicast Reverse Path Forwarding

Some of the vulnerabilities that are described in this document can be exploited by spoofed IP packets.The proper deployment and configuration of Unicast Reverse Path Forwarding (Unicast RPF) can provide protection mechanisms for spoofing related to the Malformed SIP Message Vulnerabilities.

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. The proper deployment and configuration of IPSG coupled with strict mode Unicast RPF can provide the most effective means of spoofing protection to help mitigate the Malformed SIP Message Vulnerabilities.

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

Identification: Transit Access Control Lists

After the administrator applies the tACL to an interface, the show ip access-lists command will identify the number of SCCP packets on TCP ports 2000 and 2443, SIP packets on TCP ports 5060 and 5061, SIP packets on UDP ports 5060 and 5061 and CTI Manager packets on TCP port 2748 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 2000 (32 matches)
    20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 2443 (45 matches)
    30 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 (123 matches)
    40 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 (23 matches)
    50 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5060 (19 matches)
    60 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 5061 (7 matches)
    70 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 2748 (67 matches)
    80 deny tcp any 192.168.60.0 0.0.0.255 eq 2000 (120 matches)
    90 deny tcp any 192.168.60.0 0.0.0.255 eq 2443 (32 matches)
    100 deny tcp any 192.168.60.0 0.0.0.255 eq 5060 (42 matches)
    110 deny tcp any 192.168.60.0 0.0.0.255 eq 5061 (51 matches)
    120 deny udp any 192.168.60.0 0.0.0.255 eq 5060 (26 matches)
    130 deny udp any 192.168.60.0 0.0.0.255 eq 5061 (32 matches)
    140 deny tcp any 192.168.60.0 0.0.0.255 eq 2748 (44 matches)
    150 deny ip any any (712 matches)
router#

In the preceding example, access list 150 has dropped the following packets that are received from an untrusted host or network:

  • 120 SCCP packets on TCP port 2000 for ACE line 80
  • 32 SCCP packets on TCP port 2443 for ACE line 90
  • 42 SIP packets on TCP port 5060 for ACE line 100
  • 51 SIP packets on TCP port 5061 for ACE line 110
  • 26 SIP packets on UDP port 5060 for ACE line 120
  • 32 SIP packets on UDP port 5061 for ACE line 130
  • 44 CTI Manager packets on TCP port 2748 for ACE line 140

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.

Identification: Access List Logging

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 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.

Identification: Spoofing Protection Using Unicast Reverse Path Forwarding

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, and show ip traffic commands to identify the number of packets that Unicast RPF has dropped.

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 Ethernet 0/0 internal | include drop
    --      CLI Output Truncated       --
  ip verify: via=rx (allow default), acl=0, drop=1966, sdrop=0 table IPv4:Default
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 Ethernet 0/0 | begin verify
    --      CLI Output Truncated       --
  IP verify source reachable-via RX, allow default
   1966 verification drops
   0 suppressed verification drops
router#


router#show cef drop
IPv4 CEF Drop Statistics
Slot  Encap_fail  Unresolved Unsupported    No_route      No_adj  ChkSum_Err
RP             0           0          44       1966         503           0
router#


router#show ip traffic

IP statistics:
  Rcvd:  166 total, 116 local destination
         0 format errors, 0 checksum errors, 0 bad hop count
         0 unknown protocol, 0 not a gateway
         0 security failures, 0 bad options, 0 with options
  Opts:  0 end, 0 nop, 0 basic security, 0 loose source route
         0 timestamp, 0 extended security, 0 record route
         0 stream ID, 0 strict source route, 0 alert, 0 cipso, 0 ump
         0 other
  Frags: 0 reassembled, 0 timeouts, 0 couldn't reassemble
         0 fragmented, 0 fragments, 0 couldn't fragment
  Bcast: 30 received, 154 sent
  Mcast: 0 received, 0 sent
  Sent:  284 generated, 776 forwarded
  Drop:  35 encapsulation failed, 0 unresolved, 0 no adjacency
         6 no route, 1966 unicast RPF, 0 forced drop
         0 options denied
  Drop:  0 packets with source IP address zero
  Drop:  0 packets with internal loop back IP address
         0 physical broadcast
    --      CLI Output Truncated       --
router#

In the preceding show cef drop and show ip traffic examples, Unicast RPF has dropped 1966 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.

Cisco IOS NetFlow

Identification: Traffic Flow Identification Using NetFlow Records

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 (17516 total packets):
   1-32   64   96  128  160  192  224  256  288  320  352  384  416  448  480
   .221 .413 .364 .001 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000

    512  544  576 1024 1536 2048 2560 3072 3584 4096 4608
   .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000

IP Flow Switching Cache, 278544 bytes
  153 active, 3943 inactive, 1838 added
  36093 ager polls, 0 flow alloc failures
  Active flows timeout in 30 minutes
  Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 34056 bytes
  0 active, 1024 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-WWW             97      0.0         4    40      0.0       0.2      15.5
TCP-other          982      0.0         6    40      0.0       0.1      15.5
UDP-TFTP           102      0.0         3    28      0.0       0.1      15.4
UDP-other          488      0.0         6    28      0.0       0.0      15.4
ICMP                16      0.0       399    84      0.0     398.1      12.8
Total:            1685      0.0         9    54      0.0       3.9      15.4

SrcIf         SrcIPaddress    DstIf          DstIPaddress    Pr SrcP DstP  Pkts
Et0/0         192.168.97.110  Et0/1          192.168.33.5    06 6827 A80A     4 
Et0/0         192.168.93.112  Et0/1          192.168.60.137  06 B002 13C5     3 
Et0/0         192.168.70.227  Et0/1          192.168.74.35   06 9C09 96CE     2 
Et0/0         192.168.217.3   Et0/1          192.168.60.50   06 AC8D 13C5     2 
Et0/0         192.168.13.140  Et0/1          192.168.187.226 06 C859 FB8E     1 
Et0/0         192.168.202.197 Et0/1          192.168.60.254  06 FD0B 13C4     5 
Et0/0         192.168.126.1   Et0/1          192.168.60.4    06 9AE5 098B     2 
Et0/0         192.168.196.115 Et0/1          192.168.60.128  11 FEC7 0045     5 
Et0/0         192.168.172.190 Et0/1          192.168.60.45   06 1AB9 0ABC     3 
Et0/0         192.168.110.4   Et0/1          192.168.60.211  06 F1D2 13C5     3 
Et0/0         192.168.144.45  Et0/1          192.168.179.143 06 52B3 104A     5 
Et0/0         192.168.135.219 Et0/1          192.168.60.91   06 AB90 01BB     2 
Et0/0         192.168.114.120 Et0/1          192.168.60.159  06 0D81 0ABC     3 
Et0/0         192.168.19.173  Et0/1          192.168.60.27   06 3FF9 098B     4 
Et0/0         192.168.92.255  Et0/1          192.168.60.249  06 69DC 098B     6 
Et0/0         192.168.232.24  Et0/1          192.168.207.89  11 B9B1 A0F3     3 
Et0/0         192.168.30.30   Et0/1          192.168.133.220 06 839C 29FB    10 
Et0/0         192.168.37.28   Et0/1          192.168.60.14   06 AEB8 07D0    15 
Et0/0         192.168.208.77  Et0/1          192.168.60.180  11 A01D 13C4     9 
Et0/0         192.168.116.70  Et0/1          192.168.60.15   06 B109 098B    14 
Et0/0         192.168.215.112 Et0/1          192.168.96.75   11 39B1 5929    11 
Et0/0         192.168.90.254  Et0/1          192.168.60.224  06 7CBD 13C4     1 
Et0/0         192.168.18.13   Et0/1          192.168.194.214 06 E4C6 8887    10 
Et0/0         192.168.19.44   Et0/1          192.168.60.127  06 517C 01BB     6 
Et0/0         192.168.94.255  Et0/1          192.168.60.253  06 E342 07D0    11 
Et0/0         192.168.238.177 Et0/1          192.168.60.93   06 83B2 07D0     2 
Et0/0         192.168.188.85  Et0/1          192.168.60.200  06 76BA 01BB     3 
Et0/0         192.168.52.150  Et0/1          192.168.60.125  06 991D 07D0     4 
Et0/0         192.168.83.147  Et0/1          192.168.60.29   06 7994 098B     9 
Et0/0         192.168.123.41  Et0/1          192.168.86.217  11 0DAC CD1B     1 
Et0/0         192.168.212.25  Et0/1          192.168.60.179  11 ACD1 13C5     5 
Et0/0         192.168.60.105  Et0/1          192.168.6.117   11 CADC 810D     4 
Et0/0         192.168.11.128  Et0/1          192.168.60.164  11 D94C 0045     2 
router#

In the preceding example, there are multiple flows for the following:

  • SCCP on TCP port 2000 (hex value 07D0)
  • SCCP on TCP port 2443 (hex value 098B)
  • SIP on TCP port 5060 (hex value 13C4)
  • SIP on TCP port 5061 (hex value 13C5)
  • SIP on UDP port 5060 (hex value 13C4)
  • SIP on UDP port 5061 (hex value 13C5)
  • CTI Manager on TCP port 2748 (hex value 0ABC)

This traffic is 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 SCCP traffic sent on TCP ports 2000 and 2443, SIP traffic sent on TCP ports 5060 and 5061, SIP traffic sent on UDP ports 5060 and 5061, and CTI Manager traffic sent on TCP port 2748 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
Et0/0         192.168.218.99  Et0/1          192.168.60.153  11 C998 13C4    11 
Et0/0         192.168.109.207 Et0/1          192.168.60.118  11 F7E7 13C5     5 
Et0/0         192.168.2.242   Et0/1          192.168.60.110  11 553B 13C4     6 
Et0/0         192.168.43.92   Et0/1          192.168.60.172  11 50AC 13C5     3 
Et0/0         192.168.78.45   Et0/1          192.168.60.253  11 3F5F 13C4     4 
Et0/0         192.168.245.150 Et0/1          192.168.60.135  11 A1DE 13C5     5 
Et0/0         192.168.188.42  Et0/1          192.168.60.112  11 0BE3 13C4     2 
Et0/0         192.168.90.147  Et0/1          192.168.60.226  11 A527 13C4    10 
Et0/0         192.168.176.42  Et0/1          192.168.60.86   11 4E27 13C5    11 
Et0/0         192.168.128.37  Et0/1          192.168.60.226  11 1C92 13C5     2 
router#

To view only the traffic flows for SCCP packets on TCP ports 2000 (hex value 07D0) and 2443 (hex value 098B), SIP packets on TCP ports 5060 (hex value 13C4) and 5061 (hex value 13C5), and CTI Manager packets on TCP 2748 (hex value 0ABC), the command show ip cache flow | include SrcIf|_06_.*(07D0|098B|13C4|13C5|0ABC)_ will display the related TCP NetFlow records as shown here:

TCP Flows

router#show ip cache flow | include SrcIf|_06_.*(07D0|098B|13C4|13C5|0ABC)_
SrcIf         SrcIPaddress    DstIf          DstIPaddress    Pr SrcP DstP  Pkts
Et0/0         192.168.220.228 Et0/1          192.168.60.131  06 88D4 0ABC     3 
Et0/0         192.168.152.182 Et0/1          192.168.60.179  06 4D2D 13C4     2 
Et0/0         192.168.67.38   Et0/1          192.168.60.1    06 2D90 098B     5 
Et0/0         192.168.107.23  Et0/1          192.168.60.189  06 3FAC 13C5     4 
Et0/0         192.168.169.7   Et0/1          192.168.60.50   06 0C13 13C5     4 
Et0/0         192.168.163.172 Et0/1          192.168.60.71   06 FB86 098B     4 
Et0/0         192.168.170.16  Et0/1          192.168.60.93   06 7630 0ABC     2 
Et0/0         192.168.190.55  Et0/1          192.168.60.172  06 9BB8 0ABC     4 
Et0/0         192.168.188.249 Et0/1          192.168.60.25   06 F506 07D0    18 
Et0/0         192.168.137.177 Et0/1          192.168.60.52   06 FB5A 07D0    10 
router#

Cisco ASA, PIX, and 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 SCCP packets on TCP ports 2000 and 2443, SIP packets on TCP ports 5060 and 5061, SIP packets on UDP ports 5060 and 5061 and CTI Manager packets on TCP port 2748 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 2000
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 2443
access-list tACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5060
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 5060
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 2748

!
!-- 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 2000
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 2443
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 5060
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 5060
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 2748

!
!-- 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

Mitigation: Spoofing Protection Using Unicast Reverse Path Forwarding

Some of the vulnerabilities that are described in this document can be exploited by spoofed IP packets.The proper deployment and configuration of Unicast Reverse Path Forwarding (Unicast RPF) can provide protection mechanisms for spoofing related to the Malformed SIP Message Vulnerabilities.

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.

Identification: Transit Access Control Lists

After the tACL has been applied to an interface, administrators can use the show access-list command to identify the number of SCCP packets on TCP ports 2000 and 2443, SIP packets on TCP ports 5060 and 5061, SIP packets on UDP ports 5060 and 5061 and CTI Manager packets on TCP port 2748 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; 15 elements; name hash: 0x3452703d
access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 2000 (hitcnt=7)
access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 2443 (hitcnt=6)
access-list tACL-Policy line 3 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq sip (hitcnt=11)
access-list tACL-Policy line 4 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=5)
access-list tACL-Policy line 5 extended permit udp host 192.168.100.1 192.168.60.0 255.255.255.0 eq sip (hitcnt=3) 
access-list tACL-Policy line 6 extended permit udp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=10)
access-list tACL-Policy line 7 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq ctiqbe (hitcnt=7)
access-list tACL-Policy line 8 extended deny tcp any 192.168.60.0 255.255.255.0 eq 2000 (hitcnt=74)
access-list tACL-Policy line 9 extended deny tcp any 192.168.60.0 255.255.255.0 eq 2443 (hitcnt=85) 
access-list tACL-Policy line 10 extended deny tcp any 192.168.60.0 255.255.255.0 eq sip (hitcnt=111)
access-list tACL-Policy line 11 extended deny tcp any 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=26)
access-list tACL-Policy line 12 extended deny udp any 192.168.60.0 255.255.255.0 eq sip (hitcnt=29)
access-list tACL-Policy line 13 extended deny udp any 192.168.60.0 255.255.255.0 eq 5061 (hitcnt=46)
access-list tACL-Policy line 14 extended deny tcp any 192.168.60.0 255.255.255.0 eq ctiqbe (hitcnt=72)
access-list tACL-Policy line 15 extended deny ip any any (hitcnt=104)
firewall#

In the preceding example, access list tACL-Policy has dropped the following packets received from an untrusted host or network:

  • 74 SCCP packets on TCP port 2000 for ACE line 8
  • 85 SCCP packets on TCP port 2443 for ACE line 9
  • 111 SIP packets on TCP port 5060 (sip) for ACE line 10
  • 26 SIP packets on TCP port 5061 for ACE line 11
  • 29 SIP packets on UDP port 5060 (sip) for ACE line 12
  • 46 SIP packets on UDP port 5061 for ACE line 13
  • 72 CTI Manager packets on TCP port 2748 (ctiqbe) for ACE line 14

Identification: Firewall Access List Syslog Messages

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 Security Appliance System Log Message - 106023.

Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance or the Cisco PIX 500 Series Security Appliance is in Monitoring the Security Appliance - Configuring and Managing Logs. 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
  Jan 28 2010 10:26:44: %ASA-4-106023: Deny tcp src outside:192.168.200.70/1350 
	  	dst inside:192.168.60.10/2000 by access-group "tACL-Policy" 
  Jan 28 2010 10:26:44: %ASA-4-106023: Deny tcp src outside:192.168.200.215/1350 
  		dst inside:192.168.60.10/2000 by access-group "tACL-Policy"
  Jan 28 2010 10:26:47: %ASA-4-106023: Deny tcp src outside:192.168.200.11/1350 
  		dst inside:192.168.60.10/2443 by access-group "tACL-Policy" 
  Jan 28 2010 10:26:47: %ASA-4-106023: Deny tcp src outside:192.168.200.36/1350 
  		dst inside:192.168.60.10/2443 by access-group "tACL-Policy" 
  Jan 28 2010 10:26:52: %ASA-4-106023: Deny tcp src outside:192.168.200.50/1350 
  		dst inside:192.168.60.10/2748 by access-group "tACL-Policy" 
  Jan 28 2010 10:26:56: %ASA-4-106023: Deny tcp src outside:192.168.200.106/1350 
  		dst inside:192.168.60.10/5060 by access-group "tACL-Policy" 
  Jan 28 2010 10:26:56: %ASA-4-106023: Deny tcp src outside:192.168.200.92/1350 
  		dst inside:192.168.60.99/5060 by access-group "tACL-Policy" 
  Jan 28 2010 10:26:57: %ASA-4-106023: Deny tcp src outside:192.168.200.200/1350 
  		dst inside:192.168.60.238/5061 by access-group "tACL-Policy"
  Jan 28 2010 10:27:00: %ASA-4-106023: Deny udp src outside:192.168.200.242/1570 
  		dst inside:192.168.60.10/5061 by access-group "tACL-Policy" 
  Jan 28 2010 10:27:00: %ASA-4-106023: Deny udp src outside:192.168.200.156/1570 
  		dst inside:192.168.60.96/5061 by access-group "tACL-Policy" 
  Jan 28 2010 10:27:02: %ASA-4-106023: Deny udp src outside:192.168.200.243/1570 
  		dst inside:192.168.60.10/5060 by access-group "tACL-Policy"
  Jan 28 2010 10:27:02: %ASA-4-106023: Deny udp src outside:192.168.200.130/1570 
		dst inside:192.168.60.10/5060 by access-group "tACL-Policy"
firewall#

In the preceding example, the messages logged for the tACL tACL-Policy show potentially spoofed SCCP packets on TCP ports 2000 and 2443, SIP packets on TCP ports 5060 and 5061, SIP packets on UDP ports 5060 and 5061 and CTI Manager packets on TCP port 2748 sent to the address block assigned to the affected devices.

Additional information about syslog messages for ASA and PIX security appliances is in Cisco Security Appliance System Log Messages. 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.

Identification: Spoofing Protection Using Unicast Reverse Path Forwarding

Firewall syslog message 106021 will be generated for packets denied by Unicast RPF. Additional information about this syslog message is in Cisco Security Appliance System Log Message - 106021.

Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance or the Cisco PIX 500 Series Security Appliance is in Monitoring the Security Appliance - Configuring and Managing Logs. 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 these vulnerabilities that is 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
  R1-A050-ASA5520# show logging | grep 106021
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.188 to 192.168.60.10 on interface outside
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.80 to 192.168.60.10 on interface outside
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.60 to 192.168.60.10 on interface outside
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.45 to 192.168.60.220 on interface outside
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.255 to 192.168.60.10 on interface outside
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.126 to 192.168.60.10 on interface outside
	Jan 28 2010 11:26:27: %ASA-1-106021: Deny UDP reverse path check from 
    		192.168.60.67 to 192.168.60.10 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 (rpf-violated)                                   28

firewall#

In the preceding example, Unicast RPF has dropped 28 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.

Cisco Intrusion Prevention System

Mitigation: Cisco IPS Signature Event Actions

Administrators can use Cisco Intrusion Prevention System (IPS) appliances and services modules to provide threat detection and help prevent attempts to exploit these vulnerabilities. Beginning with signature update S475 for sensors running Cisco IPS version 6.x or 5.x, these vulnerabilities can be detected by signature 24359/0 (Signature Name: CUCM Malformed SIP Message DoS). Signature 24359/0 is enabled by default, triggers a High severity event, has a signature fidelity rating (SFR) of 80, and is configured with a default event action of produce-alert.

Signature 24359/0 fires on an attempt to exploit a Denial of Service condition in Cisco's Call Manager Software. This vulnerability was addressed via CSCtc62362. 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 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.

Cisco IPS 5.x sensors that are deployed in inline protection mode require an event action configured on a per-signature basis. Alternatively, administrators can configure an override that can perform an event action for any signatures that are triggered and are calculated as a high-risk threat. Using an event action on sensors deployed in inline protection mode provides the most effective exploit prevention.

For additional information about the risk rating and threat rating calculation, reference Risk Rating and Threat Rating: Simplify IPS Policy Management.

Cisco Security Monitoring, Analysis, and Response System

Identification: Cisco Security Monitoring, Analysis, and Response System Incidents

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 24359/0 (Signature Name: CUCM Malformed SIP Message DoS). After the S475 dynamic signature update has been downloaded, using keyword NR-24359/0 for IPS signature 24359/0 and a query type of All Matching Event Raw Messages 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 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.

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

Revision 1.0

2010-March-3

Initial public release

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 http://www.cisco.com/web/about/security/psirt/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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