Cisco Applied Mitigation Bulletin

Identifying and Mitigating Exploitation of the Cisco Unified Communications Manager Skinny Client Control Protocol Vulnerabilities

Advisory ID: cisco-amb-20120229-cucm

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20120229-cucm

Revision 1.0

For Public Release 2012 February 29 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 Skinny Client Control Protocol Vulnerabilities and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

The Cisco Unified Communications Manager contains vulnerabilities when processing specially crafted Skinny Client Control Protocol (SCCP) IP version 4 (IPv4) and IP version 6 (IPv6) packets. These vulnerabilities can be exploited remotely without authentication and without end user interaction. Successful exploitation of these vulnerabilities could cause the affected device to reload or allow arbitrary code execution. Repeated attempts to exploit this vulnerability may result in a sustained DoS condition.

The attack vectors for exploitation are through IPv4 and IPv6 packets using the following protocols and ports:

  • SCCP using TCP port 2000
  • SCCP using TCP port 2443

These vulnerabilities have been assigned Common Vulnerabilities and Exposures (CVE) identifiers CVE-2011-4486 and CVE-2011-4487.

Vulnerability Overview

Information about vulnerable, unaffected, and fixed software is available in the Cisco Security Advisory which is available at the following link: http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120229-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 transit access control lists (tACLs).

This protection mechanism filters and drops packets that are attempting to exploit these vulnerabilities.

Effective exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance, Cisco Catalyst 6500 Series ASA Services Module (ASASM), and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers using transit access control lists (tACLs).

This protection mechanism filters and drops packets that are attempting to exploit these vulnerabilities.

Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.

Cisco IOS Software, Cisco ASA, Cisco ASASM, Cisco FWSM firewalls, and Cisco ACE Application Control Engine Appliance and Module can provide visibility through syslog messages and counter values displayed in the output from show commands.

The Cisco Security Manager 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: The effectiveness of any mitigation technique is dependent 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 IPv4 and IPv6 packets on TCP ports 2000 and 2443 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 protocols and 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
!
!-- 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
!
!-- 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 protocols and ports
!
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 2000 permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 2443 !
!-- The following vulnerability-specific ACEs can
!-- aid in identification of attacks to global and
!-- link-local addresses
!
deny tcp any 2001:DB8:1:60::/64 eq 2000 deny tcp any 2001:DB8:1:60::/64 eq 2443 !
!-- 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 interfaces 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 command(s) no ip unreachables and no ipv6 unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration command(s) ip icmp rate-limit unreachable interval-in-ms and ipv6 icmp error-interval interval-in-ms.

Identification: Transit Access Control Lists

After the administrator applies the tACL to an interface, show ip access-lists and show ipv6 access-list commands will identify the number of SCCP IPv4 and IPv6 packets on TCP ports 2000 and 2443 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 and show ipv6 access-list IPv6-Transit-ACL-Policy 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
    20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 2443
    30 deny tcp any 192.168.60.0 0.0.0.255 eq 2000 (17 matches)
40 deny tcp any 192.168.60.0 0.0.0.255 eq 2443 (11 matches)
50 deny ip any any
router#

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

  • 17 SCCP packets on TCP port 2000 for ACE line 30
  • 11 SCCP packets on TCP port 2443 for ACE line 40
router#show ipv6 access-list IPv6-Transit-ACL-Policy 
IPv6 access list IPv6-Transit-ACL-Policy
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 2000 (55 matches) sequence 10
permit tcp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 2443 (38 matches) sequence 20
deny tcp any 2001:DB8:1:60::/64 eq 2000 (37 matches) sequence 30
deny tcp any 2001:DB8:1:60::/64 eq 2443 (41 matches) sequence 40
permit icmp any any nd-ns (41 matches) sequence 50
permit icmp any any nd-na (41 matches) sequence 60
deny ipv6 any any (21 matches) sequence 70

In the preceding example, access list IPv6-Transit-ACL-Policy has dropped the following packets received from an untrusted host or network:

  • 37 SCCP packets on TCP port 2000 for ACE line 30
  • 41 SCCP packets on TCP port 2443 for ACE line 40

For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Cisco Security Intelligence Operations white paper.

Administrators can use Cisco IOS Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Cisco Security Intelligence Operations 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: 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 IPv4 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 Cisco Security Intelligence Operations white paper.

Cisco IOS NetFlow and Cisco IOS Flexible NetFlow

Identification: IPv4 Traffic Flow Identification Using Cisco IOS NetFlow

Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of IPv4 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 (90784136 total packets):
   1-32   64   96  128  160  192  224  256  288  320  352  384  416  448  480
   .000 .698 .011 .001 .004 .005 .000 .004 .000 .000 .003 .000 .000 .000 .000

    512  544  576 1024 1536 2048 2560 3072 3584 4096 4608
   .000 .001 .256 .000 .010 .000 .000 .000 .000 .000 .000

IP Flow Switching Cache, 4456704 bytes
  1885 active, 63651 inactive, 59960004 added
  129803821 ager polls, 0 flow alloc failures
  Active flows timeout in 30 minutes
  Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 402056 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    11393421      2.8         1    48      3.1       0.0       1.4
TCP-FTP            236      0.0        12    66      0.0       1.8       4.8
TCP-FTPD            21      0.0     13726  1294      0.0      18.4       4.1
TCP-WWW          22282      0.0        21  1020      0.1       4.1       7.3
TCP-X              719      0.0         1    40      0.0       0.0       1.3
TCP-BGP              1      0.0         1    40      0.0       0.0      15.0
TCP-Frag         70399      0.0         1   688      0.0       0.0      22.7
TCP-other     47861004     11.8         1   211     18.9       0.0       1.3
UDP-DNS            582      0.0         4    73      0.0       3.4      15.4
UDP-NTP         287252      0.0         1    76      0.0       0.0      15.5
UDP-other       310347      0.0         2   230      0.1       0.6      15.9
ICMP             11674      0.0         3    61      0.0      19.8      15.5
IPv6INIP            15      0.0         1  1132      0.0       0.0      15.4
GRE                  4      0.0         1    48      0.0       0.0      15.3 
Total:        59957957     14.8         1   196     22.5       0.0       1.5

SrcIf         SrcIPaddress    DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.10.201  Gi0/1         192.168.60.102  06 0984 07D0     4
Gi0/0         192.168.11.54   Gi0/1         192.168.60.158  06 0911 098B     7
Gi0/1         192.168.150.60  Gi0/0         10.89.16.226    11 0016 12CA     1
Gi0/0         192.168.13.97   Gi0/1         192.168.60.28   06 0B3E 07D0     8
Gi0/0         10.88.226.1     Gi0/1         192.168.202.22  11 007B 007B     1
Gi0/0         10.89.16.226    Gi0/1         192.168.150.60  06 12CA 0016     1
router#

In the preceding example, there are multiple flows for SCCP on TCP port 2000 (hex value 07D0) and TCP port 2443 (hex value 098B).

As shown in the following example, to view only the SCCP packets on TCP port 2000 (hex value 07D0) and TCP port 2443 (hex value 098B), use the show ip cache flow | include SrcIf|_06_.*(07D0|098B)_ command to display the related Cisco NetFlow records:

TCP Flows
router#show ip cache flow | include SrcIf|_06_.*(07D0|098B)_
SrcIf         SrcIPaddress     DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.12.110   Gi0/1         192.168.60.163  06 092A 07D0     6
Gi0/0         192.168.11.230   Gi0/1         192.168.60.20   06 0C09 07D0     1
Gi0/0         192.168.11.131   Gi0/1         192.168.60.245  06 0B66 098B    18
Gi0/0         192.168.13.7     Gi0/1         192.168.60.162  06 0914 07D0     1
router#

Identification: IPv6 Traffic Flow Identification Using Cisco IOS NetFlow

Administrators can configure Cisco IOS NetFlow on Cisco IOS routers and switches to aid in the identification of IPv6 traffic flows that may be attempts to exploit the vulnerabilities that are described in this document. Administrators are advised to investigate flows to determine whether they are attempts to exploit these vulnerabilities or whether they are legitimate traffic flows.

The following output is from a Cisco IOS device running Cisco IOS Software 12.4 mainline train. The command syntax will vary for different Cisco IOS Software trains.

router#show ipv6 flow cache

IP packet size distribution (50078919 total packets):
   1-32  64   96  128  160  192  224  256  288  320  352  384  416  448  480
   .000 .990 .001 .008 .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, 475168 bytes
8 active, 4088 inactive, 6160 added
1092984 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 33928 bytes
16 active, 1008 inactive, 12320 added, 6160 added to flow
0 alloc failures, 0 force free
1 chunk, 1 chunk added
SrcAddress        InpIf    DstAddress       OutIf    Prot SrcPrt DstPrt Packets
2001:DB...06::201 Gi0/0 2001:DB...28::20 Local 0x06 0x16C4 0x07D0 1464 2001:DB...6A:5BA6 Gi0/0 2001:DB...28::21 Gi0/1 0x3A 0x0000 0x8000 1191 2001:DB...6A:5BA6 Gi0/0 2001:DB...134::3 Gi0/1 0x3A 0x0000 0x8000 1191 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::4 Gi0/1 0x3A 0x0000 0x8000 1192 2001:DB...6A:5BA6 Gi0/0 2001:DB...128::2 Gi0/1 0x06 0x160A 0x07D0 1597 2001:DB...06::201 Gi0/0 2001:DB...128::3 Gi0/1 0x06 0x1610 0x098B 1001
2001:DB...6A:5BA6 Gi0/0 2001:DB...128::3 Gi0/1 0x3A 0x0000 0x8000 1155
2001:DB...6A:5BA6 Gi0/0 2001:DB...146::3 Gi0/1 0x3A 0x0000 0x8000 1092
2001:DB...6A:5BA6 Gi0/0 2001:DB...144::4 Gi0/1 0x3A 0x0000 0x8000 1193

To permit display of the full 128-bit IPv6 address, use the terminal width 132 exec mode command.

In the preceding example, there are multiple IPv6 flows for SCCP on TCP port 2000 (hex value 07D0) and TCP port 2443 (hex value 098B).

As shown in the following example, to view only the SCCP packets on TCP port 2000 (hex value 07D0) and TCP port 2443 (hex value 098B), use the show ipv6 flow cache | include SrcIf|_06_.*(07D0|098B)_ command to display the related Cisco NetFlow records:

TCP Flows

router#show ipv6 flow cache | include SrcIf|_06_.*(07D0|098B)_
SrcAddress        InpIf    DstAddress       OutIf    Prot SrcPrt DstPrt Packets
2001:DB...6A:5BA6 Gi0/0    2001:DB...128::2 Gi0/1    0x06 0x160A 0x13C4 1597
2001:DB...06::201 Gi0/0    2001:DB...128::3 Gi0/1    0x06 0x1610 0x098B 1001
router#

Identification: IPv4 Traffic Flow Identification Using Cisco Flexible NetFlow

Introduced in Cisco IOS Software Releases 12.2(31)SB2 and 12.4(9)T, Cisco IOS Flexible NetFlow improves original Cisco NetFlow by adding the capability to customize the traffic analysis parameters for the administrator's specific requirements. Original Cisco NetFlow uses a fixed seven tuples of IP information to identify a flow, whereas Cisco IOS Flexible NetFlow allows the flow to be user defined. It facilitates the creation of more complex configurations for traffic analysis and data export by using reusable configuration components.

The following example output is from a Cisco IOS device that is running a version of Cisco IOS Software in the 15.1T train. Although the syntax will be almost identical for the 12.4T and 15.0 trains, it may vary slightly depending on the actual Cisco IOS release being used. In the following configuration, Cisco IOS Flexible NetFlow will collect information on interface GigabitEthernet0/0 for incoming IPv4 flows based on source IPv4 address, as defined by the match ipv4 source address key field statement. Cisco IOS Flexible NetFlow will also include nonkey field information about source and destination IPv4 addresses, protocol, ports (if present), ingress and egress interfaces, and packets per flow.

!
!-- Configure key and nonkey fields
!-- in the user-defined flow record
!
flow record FLOW-RECORD-ipv4 match ipv4 source address collect ipv4 protocol collect ipv4 destination address collect transport source-port collect transport destination-port collect interface input collect interface output collect counter packets !
!-- Configure the flow monitor to
!-- reference the user-defined flow
!-- record
!
flow monitor FLOW-MONITOR-ipv4 record FLOW-RECORD-ipv4 !
!-- Apply the flow monitor to the interface
!-- in the ingress direction
!
interface GigabitEthernet0/0 ip flow monitor FLOW-MONITOR-ipv4 input

The Cisco IOS Flexible NetFlow flow output is as follows:

router#show flow monitor FLOW-MONITOR-ipv4 cache format table
  Cache type:                               Normal
  Cache size:                                 4096
  Current entries:                               6
  High Watermark:                                1

  Flows added:                                   9181
  Flows aged:                                    9175
    - Active timeout      (  1800 secs)          9000
    - Inactive timeout    (    15 secs)           175
    - Event aged                                    0
    - Watermark aged                                0
    - Emergency aged                                0

IPV4 SRC ADDR    ipv4 dst addr    trns src port  trns dst port  intf input     intf output     pkts     ip prot
===============  ===============  =============  =============  =============  ==============  =======  =======
 192.168.10.201   192.168.60.102           1456           2000          Gi0/0           Gi0/1     1128       6
 192.168.13.97     192.168.60.28           3451           2443          Gi0/0           Gi0/1        1       6
   10.88.226.1    192.168.202.22           2678            443          Gi0/0           Gi0/1    10567       6
  10.89.16.226    192.168.150.60           3562             80          Gi0/0           Gi0/1    30012       6

To view only the SCCP on TCP port 2000 and TCP port 2443, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_6_.*(2000|2443)_ command to display the related NetFlow records.

For more information about Cisco IOS Flexible NetFlow, refer to Flexible Netflow Configuration Guide, Cisco IOS Release 15.1M&T and Cisco IOS Flexible NetFlow Configuration Guide, Release 12.4T.

Identification: IPv6 Traffic Flow Identification Using Cisco IOS Flexible NetFlow

The following example output is from a Cisco IOS device that is running a version of Cisco IOS Software in the 15.1T train. Although the syntax will be almost identical for the 12.4T and 15.0 trains, it may vary slightly depending on the actual Cisco IOS release being used. In the following configuration, Cisco IOS Flexible NetFlow will collect information on interface GigabitEthernet0/0 for incoming IPv6 flows based on the source IPv6 address, as defined by the match ipv6 source address key field statement. Cisco IOS Flexible NetFlow will also include nonkey field information about source and destination IPv6 addresses, protocol, ports (if present), ingress and egress interfaces, and packets per flow.
!
!-- Configure key and nonkey fields
!-- in the user-defined flow record
!
flow record FLOW-RECORD-ipv6 match ipv6 source address collect ipv6 protocol collect ipv6 destination address collect transport source-port collect transport destination-port collect interface input collect interface output collect counter packets !
!-- Configure the flow monitor to
!-- reference the user-defined flow
!-- record
!
flow monitor FLOW-MONITOR-ipv6 record FLOW-RECORD-ipv6 !
!-- Apply the flow monitor to the interface
!-- in the ingress direction
!
interface GigabitEthernet0/0 ipv6 flow monitor FLOW-MONITOR-ipv6 input

The Cisco IOS Flexible NetFlow flow output is as follows:

router#show flow monitor FLOW-MONITOR-ipv6 cache format table
  Cache type:                               Normal
  Cache size:                                 4096
  Current entries:                               6
  High Watermark:                                2

  Flows added:                                   539
  Flows aged:                                    532
    - Active timeout      (  1800 secs)          350
    - Inactive timeout    (    15 secs)          182
    - Event aged                                   0
    - Watermark aged                               0
    - Emergency aged                               0

IPV6 SRC ADDR       ipv6 dst addr       trns src port  trns dst port  intf input   intf output   pkts        ip prot
==================  ==================  =============  =============  ===========  ============  ==========  =======
 2001:DB...06::201    2001:DB...28::20            123            123        Gi0/0         Gi0/0          17       17
 2001:DB...06::201    2001:DB...28::20           1265           2000        Gi0/0         Gi0/0        1237        6
 2001:DB...06::201    2001:DB...28::20           1441           2443        Gi0/0         Gi0/0        2346        6
 2001:DB...06::201    2001:DB...28::20           1890           2000        Gi0/0         Gi0/0        5009        6
 2001:DB...06::201    2001:DB...28::20           2856           5060        Gi0/0         Gi0/0         486       17
 2001:DB...06::201    2001:DB...28::20           3012             53        Gi0/0         Gi0/0        1016       17
 2001:DB...06::201    2001:DB...28::20           2477             53        Gi0/0         Gi0/0        1563       17

To permit display of the full 128-bit IPv6 address, use the terminal width 132 exec mode command.

To view only the SCCP on TCP port 2000 and TCP port 2443, use the show flow monitor FLOW-MONITOR-ipv6 cache format table | include IPV6 DST ADDR|_6_.*(2000|2443)_ command to display the related Cisco IOS Flexible NetFlow records.

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 these vulnerabilities when the attack originates from a trusted source address.

The tACL policy denies unauthorized SCCP IPv4 and IPv6 packets on TCP ports 2000 and 2443 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 protocols and 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
!
!-- 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
!
!-- 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
!
!-- Create the corresponding IPv6 tACL
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable protocols and ports
!
ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:db8:1:60::/64 eq 2000 ipv6 access-list IPv6-tACL-Policy permit tcp host 2001:DB8::100:1 2001:db8:1:60::/64 eq 2443 !
!-- The following vulnerability-specific access control entries
!-- (ACEs) can aid in identification of attacks
!
ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:db8:1:60::/64 eq 2000 ipv6 access-list IPv6-tACL-Policy deny tcp any 2001:db8:1:60::/64 eq 2443 !
!-- 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
!
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

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 IPv4 and IPv6 packets on TCP ports 2000 and 2443 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 and show access-list IPv6-tACL-Policy follows:

firewall#show access-list tACL-Policy
access-list tACL-Policy; 5 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=31)
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=61)
access-list tACL-Policy line 3 extended deny tcp any 192.168.60.0 
     255.255.255.0 eq 2000 (hitcnt=8)
access-list tACL-Policy line 4 extended deny tcp any 192.168.60.0
255.255.255.0 eq 2443 (hitcnt=14)
access-list tACL-Policy line 5 extended deny ip any any (hitcnt=8)

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

  • 8 SCCP packets on TCP port 2000 for ACE line 3
  • 14 SCCP packets on TCP port 2443 for ACE line 4
firewall#show access-list IPv6-tACL-Policy                 
ipv6 access-list IPv6-tACL-Policy; 5 elements; name hash: 0x566a4229
ipv6 access-list IPv6-tACL-Policy line 1 permit tcp host 2001:db8:1:100::1
2001:db8:1:60::/64 eq 2000 (hitcnt=59)
ipv6 access-list IPv6-tACL-Policy line 2 permit tcp host 2001:db8:1:100::1
2001:db8:1:60::/64 eq 2443 (hitcnt=28)
ipv6 access-list IPv6-tACL-Policy line 3 deny tcp any
2001:db8:1:60::/64 eq 2000 (hitcnt=47) ipv6 access-list IPv6-tACL-Policy line 4 deny tcp any 2001:db8:1:60::/64 eq 2443 (hitcnt=33) ipv6 access-list IPv6-tACL-Policy line 5 deny ip any any (hitcnt=27)

In the preceding example, access list IPv6-tACL-Policy has dropped the following packets received from an untrusted host or network:

  • 47 SCCP packets on TCP port 2000 for ACE line 3
  • 33 SCCP packets on TCP port 2443 for ACE line 4

In addition, syslog message 106023 can provide valuable information, which includes the source and destination IP address, the source and destination port numbers, and the IP protocol for the denied packet.

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 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 Cisco Catalyst 6500 Series ASA Services Module is in 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
  Feb 29 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.18/2944 
         dst inside:192.168.60.191/2000 by access-group "tACL-Policy"
  Feb 29 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.200/2945 
         dst inside:192.168.60.33/2443 by access-group "tACL-Policy"
  Feb 29 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:192.0.2.99/2946 
         dst inside:192.168.60.240/2443 by access-group "tACL-Policy"
  Feb 29 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:2001:db8:2::2:172/2951
         dst inside:2001:db8:1:60::23/2000 by access-group "IPv6-tACL-Policy"
  Feb 29 2012 00:15:13: %ASA-4-106023: Deny tcp src outside:2001:db8:d::a85e:172/2952
         dst inside:2001:db8:1:60::134/2443 by access-group "IPv6-tACL-Policy"
firewall#

In the preceding example, the messages logged for the tACL tACL-Policy show SCCP packets for TCP ports 2000 and 2443 sent to the address block assigned to the affected devices.

Additional information about syslog messages for Cisco ASA Series Adaptive Security Appliances is in Cisco ASA 5500 Series System Log Messages, 8.2. Additional information about syslog messages for Cisco Catalyst 6500 Series ASA Services Module is in the Analyzing Syslog Messages section of the Cisco ASASM CLI Configuration Guide. Additional information about syslog messages for the Cisco 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 Cisco Security Intelligence Operations white paper.

Cisco Security Manager

Identification: Cisco Security Manager

Cisco Security Manager, Event Viewer

Beginning in software version 4.0, Cisco Security Manager can collect syslogs from Cisco firewalls and provides the Event Viewer, which can query for events that are related to the vulnerabilities that are described in this document.

Using the following filters in the Firewall Denied Events predefined view in the Event Viewer provides all captured Cisco firewall access list deny syslog messages that could indicate potential attempts to exploit the vulnerabilities that are described in this document.

  • Use the Destination event filter to filter network objects that contain the IP address space that is used by the affected devices (for example, IPv4 address range 192.168.60.0/24 and IPv6 address range 2001:DB8:1:60::/64)
  • Use the Destination Service event filter to filter objects that contain TCP ports 2000 and 2443

An Event Type ID filter can be used with the Firewall Denied Events predefined view in the Event Viewer to filter the syslog IDs shown in the following list to provide all captured Cisco firewall deny syslog messages that could indicate potential attempts to exploit the vulnerabilities that are described in this document:

  • ASA-4-106023 (ACL deny)

For more information about Cisco Security Manager Events, refer to the Filtering and Querying Events section of the Cisco Security Manager User Guide.

Identification: Event Management System Partner Events

Cisco works with industry-leading Security Information and Event Management (SIEM) companies through the Cisco Developer Network. This partnership helps Cisco deliver validated and pretested SIEM systems that address business concerns such as long-term log archiving and forensics, heterogeneous event correlation, and advanced compliance reporting. Security Information and Event Management partner products can be leveraged to collect events from Cisco devices and then query the collected events for the incidents created by a Cisco IPS signature or deny syslog messages from firewalls that could indicate potential attempts to exploit the vulnerabilities that are described in this document. The queries can be made by Sig ID and Syslog ID as shown in the following list:

  • ASA-4-106023 (ACL deny)

For more information about SIEM partners, refer to the Security Management System website.


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 2012-February-29 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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