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Cisco Applied Mitigation Bulletin

Cisco Applied Mitigation Bulletin: Identifying and Mitigating Multiple Vulnerabilities in QNX

 
Threat Type:IntelliShield: Applied Mitigation Bulletin
IntelliShield ID:30064
Version:1
First Published:2013 July 15 20:02 GMT
Last Published:2013 July 15 20:02 GMT
Port: 4868
CVE:CVE-2013-2687 , CVE-2013-2688
Urgency:Unlikely Use
Credibility:Confirmed
Severity:Moderate Damage
 
Version Summary:Cisco Applied Mitigation Bulletin initial public release
 

Cisco Response

A vulnerability in multiple QNX products could allow an unauthenticated, remote attacker to execute arbitrary code or cause a denial of service (DoS) condition.

A vulnerability in processing certain packets by multiple QNX products could allow an unauthenticated, remote attacker to cause a DoS condition.

Vulnerability Characteristics

Details of these vulnerabilities are described in IntelliShield Alerts 30056 and 30057.

Mitigation Technique Overview

Cisco IOS Software can provide effective means of exploit prevention using the following methods:

  • Transit access control lists (tACLs)
  • Unicast Reverse Path Forwarding (uRPF)
  • IP source guard (IPSG)

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

The proper deployment and configuration of uRPF provides an effective means of protection against attacks that use packets with spoofed source IP addresses. uRPF should be deployed as close to all traffic sources as possible.

The proper deployment and configuration of IPSG provides an effective means of protection against spoofed packets at the access layer.

Effective means of exploit prevention can also be provided by 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 the following methods:

  • tACLs
  • uRPF

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

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

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

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 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 this vulnerability when the attack originates from a trusted source address.

The tACL policy denies unauthorized phrelay IPv4 and IPv6 packets on UDP port 4868 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 available in Transit Access Control Lists: Filtering at Your Edge.

!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable port
!
access-list 150 permit udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 4868
!
!-- The following vulnerability-specific access control entry 
!-- (ACE) can aid in identification of attacks
!
access-list 150 deny udp any 192.168.60.0 0.0.0.255 eq 4868
!
!-- 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 port
  !
  permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 4868
  !
  !-- The following vulnerability-specific ACE can 
  !-- aid in identification of attacks to global and
  !-- link-local addresses
  !
  deny udp any 2001:DB8:1:60::/64 eq 4868
  !
  !-- 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 commands no ip unreachables and no ipv6 unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration commands ip icmp rate-limit unreachable interval-in-ms and ipv6 icmp error-interval interval-in-ms.

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 phrelay IPv4 and IPv6 packets on UDP port 4868 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit this vulnerability. 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 udp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 4868
    20 deny udp any 192.168.60.0 0.0.0.255 eq 4868 (97 matches)
    30 deny ip any any
router#

In the preceding example, access list 150 has dropped 97 phrelay packets on UDP port 4868 for access control list entry (ACE) line 20.

router#show ipv6 access-list IPv6-Transit-ACL-Policy 
IPv6 access list IPv6-Transit-ACL-Policy
    permit udp host 2001:DB8::100:1 2001:DB8:1:60::/64 eq 4868 (210 matches) sequence 10
    udp any 2001:DB8:1:60::/64 eq 4868 (29 matches) sequence 20
    permit icmp any any nd-ns (23 matches) sequence 30
    permit icmp any any nd-na (23 matches) sequence 40
    deny ipv6 any any (23 matches) sequence 50

In the preceding example, access list IPv6-Transit-ACL-Policy has dropped 29 phrelay packets on UDP port 4868 for access control list entry (ACE) line 20.

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 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.


Mitigation: Spoofing Protection

Unicast Reverse Path Forwarding

The vulnerability described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure Unicast Reverse Path Forwarding (uRPF) as a protection mechanism against spoofing.

uRPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on uRPF to provide complete spoofing protection because spoofed packets may enter the network through a uRPF-enabled interface if an appropriate return route to the source IP address exists. Administrators are advised to take care to ensure that the appropriate uRPF mode (loose or strict) is configured during the deployment of this feature because it can drop legitimate traffic that is transiting the network. In an enterprise environment, uRPF may be enabled at the Internet edge and the internal access layer on the user-supporting Layer 3 interfaces.

Additional information is available in the Unicast Reverse Path Forwarding Loose Mode Feature Guide.

For additional information about the configuration and use of uRPF, reference the Understanding Unicast Reverse Path Forwarding Cisco Security Intelligence Operations white paper.

IP Source Guard

IP source guard (IPSG) is a security feature that restricts IP traffic on nonrouted, Layer 2 interfaces by filtering packets based on the DHCP snooping binding database and manually configured IP source bindings. Administrators can use IPSG to prevent attacks from an attacker who attempts to spoof packets by forging the source IP address and/or the MAC address. When properly deployed and configured, IPSG coupled with strict mode uRPF provides the most effective means of spoofing protection for the vulnerability described in this document.

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

Identification: Spoofing Protection Using Unicast Reverse Path Forwarding

With uRPF 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 uRPF has dropped.

Note: Beginning with Cisco IOS Software Release 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
  IPv6 unicast RPF: via=rx acl=None, drop=10, sdrop=0 (if IPv6 applies) 
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 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 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 ipv6 interface GigabitEthernet 0/0 | section IPv6 verify

  IPv6 verify source reachable-via rx 
  0 verification drop(s) (process), 10 (CEF)
  0 suppressed verification drop(s) (process), 0 (CEF)
  --      CLI Output Truncated       --  
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 ipv6 cef switching statistics feature IPv6 CEF input features: Feature Drop Consume Punt Punt2Host Gave route RP LES Verify Unicast R 10 0 0 0 0 Total 10 0 0 0 0 -- CLI Output Truncated -- router# router#show ip traffic | include RPF 18 no route, 18 unicast RPF, 0 forced drop router# router#show ipv6 traffic | include RPF 10 RPF drops, 0 RPF suppressed, 0 forced drop router#

In the preceding show cef interface type slot/port internal, show cef drop, show ip interface type slot/port and show ipv6 interface type slot/port, show ip cef switching statistics feature and show ipv6 cef switching statistics feature, and show ip traffic and show ipv6 traffic examples, uRPF has dropped the following packets received globally on all interfaces with uRPF configured because of the inability to verify the source address of the IP packets within the forwarding information base of Cisco Express Forwarding.

  • 18 IPv4 packets
  • 10 IPv6 packets

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 the vulnerability described in this document. Administrators are advised to investigate flows to determine whether they are attempts to exploit the vulnerability 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  11 4F33 1304    67
Gi0/0         192.168.11.54   Gi0/1         192.168.60.158  11 0911 00A1     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 4F34 1304     4
Gi0/0         192.168.10.17   Gi0/1         192.168.60.97   11 4F35 1304    80
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 4F36 1304   191
Gi0/0         10.89.16.226    Gi0/1         192.168.150.60  06 12CA 0016     1

In the preceding example, there are multiple flows for phrelay on UDP port 4868 (hex value 1304).

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 this vulnerability. Administrators are advised to compare these flows to baseline utilization for phrelay traffic sent on UDP port 4868 and also investigate the flows to determine whether they are sourced from untrusted hosts or networks.

As shown in the following example, to view only the traffic flows for phrelay packets on UDP port 4868 (hex value 1304), use the show ip cache flow | include SrcIf|_11_.*1304 command to display the related Cisco NetFlow records:

UDP Flows

router#show ip cache flow | include SrcIf|_11_.*1304

SrcIf         SrcIPaddress     DstIf         DstIPaddress    Pr SrcP DstP  Pkts
Gi0/0         192.168.11.230   Gi0/1         192.168.60.20   11 0C09 1304    22
Gi0/0         192.168.11.131   Gi0/1         192.168.60.245  11 0B66 1304    70
Gi0/0         192.168.13.7     Gi0/1         192.168.60.162  11 0914 1304    12

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 vulnerability that is described in this document. Administrators are advised to investigate flows to determine whether they are attempts to exploit this vulnerability 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    0x11 0x16C4 0x1304 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 0x1304 1597
2001:DB...06::201 Gi0/0    2001:DB...128::3 Gi0/1    0x11 0x1610 0x1304 1001  
2001:DB...06::201 Gi0/0    2001:DB...128::4 Gi0/1    0x11 0x1634 0x1304 1292  
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 phrelay on UDP port 4868 (hex value 1304).

The phrelay packets on UDP port 4868 are sourced from and sent to addresses within the 2001:DB8:1:60::/64 address block that is used by affected devices. The packets in the UDP flows may be spoofed and could indicate an attempt to exploit this vulnerability. Administrators are advised to compare these flows to baseline utilization for phrelay traffic on UDP port 4868 and also investigate the flows to determine whether they are sourced from untrusted hosts or networks.

As shown in the following example, to view only the phrelay packets on UDP port 4868 (hex value 1304), use the show ipv6 flow cache | include SrcIf|_11_.*1304 command to display the related Cisco NetFlow records:

UDP Flows

router#show ip cache flow | include SrcIf|_11_.*1304_
SrcAddress        InpIf    DstAddress       OutIf    Prot SrcPrt DstPrt Packets
2001:DB...06::201 Gi0/0    2001:DB...28::20 Local    0x11 0x16C4 0x1304 1464 
2001:DB...06::201 Gi0/0    2001:DB...128::3 Gi0/1    0x11 0x1610 0x1304  337 
2001:DB...06::201 Gi0/0    2001:DB...128::4 Gi0/1    0x11 0x1634 0x1304 1565 
router#

Identification: IPv4 Traffic Flow Identification Using Cisco IOS 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            80      Gi0/0       Gi0/1 1128       6
 192.168.11.54 192.168.60.158          8910          4868      Gi0/0       Gi0/1 2212      17
192.168.150.60   10.89.16.226          2567           443      Gi0/0       Gi0/1   13       6
 192.168.13.97  192.168.60.28          3451            80      Gi0/0       Gi0/1    1       6
 192.168.10.17  192.168.60.97          8911          4868      Gi0/0       Gi0/1   16      17
   10.88.226.1 192.168.202.22          2678           443      Gi0/0       Gi0/1 8567       6
  10.89.16.226 192.168.150.60          3562            80      Gi0/0       Gi0/1 4012       6

To view only the phrelay on UDP port 4868, use the show flow monitor FLOW-MONITOR-ipv4 cache format table | include IPV4 DST ADDR |_4868.*_17_ 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            80      Gi0/0       Gi0/0 1237       6
2001:DB...06::201 2001:DB...28::20          9102          4868      Gi0/0       Gi0/0 2346      17
2001:DB...06::201 2001:DB...28::20          1890            80      Gi0/0       Gi0/0 5009       6
2001:DB...06::201 2001:DB...28::20          9103          4868      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 phrelay on UDP port 4868, use the show flow monitor FLOW-MONITOR-ipv6 cache format table | include IPV6 DST ADDR|_4868.*_17_ 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 this vulnerability when the attack originates from a trusted source address.

The tACL policy denies unauthorized phrelay IPv4 and IPv6 packets on UDP port 4868 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 port
!
access-list tACL-Policy extended permit udp host 192.168.100.1 
     192.168.60.0 255.255.255.0 eq 4868
!
!-- The following vulnerability-specific ACE
!-- can aid in identification of attacks
!
access-list tACL-Policy extended deny udp any 192.168.60.0 255.255.255.0 eq 4868
!
!-- 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 port
!
ipv6 access-list IPv6-tACL-Policy permit udp host 2001:DB8::100:1
          2001:db8:1:60::/64 eq 4868
!
!--  The following vulnerability-specific access control entries
!--  (ACE) can aid in identification of attacks
!
ipv6 access-list IPv6-tACL-Policy deny udp any 2001:db8:1:60::/64 eq 4868
!
!--  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 phrelay IPv4 and IPv6 packets on UDP port 4868 that have been filtered. Administrators are advised to investigate filtered packets to determine whether they are attempts to exploit this vulnerability. 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; 3 elements; name hash: 0x3452703d
access-list tACL-Policy line 1 extended permit udp host 192.168.100.1 
     192.168.60.0 255.255.255.0 eq 4868 (hitcnt=14)
access-list tACL-Policy line 2 extended deny udp any 192.168.60.0 
     255.255.255.0 eq 4868 (hitcnt=30)
access-list tACL-Policy line 3 extended deny ip any any (hitcnt=8)

In the preceding example, access list tACL-Policy has dropped 14 phrelay packets on UDP port 4868 received from an untrusted host or network. 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.

firewall#show access-list IPv6-tACL-Policy                 
ipv6 access-list IPv6-tACL-Policy; 3 elements; name hash: 0x566a4229
ipv6 access-list IPv6-tACL-Policy line 1 permit udp host 2001:db8:1:100::1 
     2001:db8:1:60::/64 eq 4868 (hitcnt=4) 
ipv6 access-list IPv6-tACL-Policy line 2 deny udp any 
     2001:db8:1:60::/64 eq 4868 (hitcnt=30) 
ipv6 access-list IPv6-tACL-Policy line 3 deny ip any any (hitcnt=18)

In the preceding example, access list IPv6-tACL-Policy has dropped 30 phrelay packets on UDP port 4868 received from an untrusted host or network. 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 vulnerability 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 106023
   Jul 12 2013 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.18/2334 
         dst inside:192.168.60.191/4868 by access-group "tACL-Policy"
   Jul 12 2013 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.200/2335 
         dst inside:192.168.60.33/4868 by access-group "tACL-Policy"
   Jul 12 2013 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.99/2336 
         dst inside:192.168.60.240/4868 by access-group "tACL-Policy"
   Jul 12 2013 00:15:13: %ASA-4-106023: Deny udp src outside:192.0.2.100/2337 
         dst inside:192.168.60.115/4868 by access-group "tACL-Policy"
   Jul 12 2013 00:15:13: %ASA-4-106023: Deny udp src outside:2001:db8:2::2:172/2341
         dst inside:2001:db8:1:60::23/4868 by access-group "IPv6-tACL-Policy"
   Jul 12 2013 00:15:13: %ASA-4-106023: Deny udp src outside:2001:db8:d::a85e:172/2342
         dst inside:2001:db8:1:60::134/4868 by access-group "IPv6-tACL-Policy"
firewall#

In the preceding example, the messages logged for the tACL tACL-Policy show potentially spoofed phrelay packets for UDP port 4868 sent to the address block assigned to 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.


Mitigation: Spoofing Protection Using Unicast Reverse Path Forwarding

The vulnerability that is described in this document can be exploited by spoofed IP packets. Administrators can deploy and configure uRPF as a protection mechanism against spoofing.

uRPF is configured at the interface level and can detect and drop packets that lack a verifiable source IP address. Administrators should not rely on uRPF to provide complete spoofing protection because spoofed packets may enter the network through a uRPF-enabled interface if an appropriate return route to the source IP address exists. In an enterprise environment, uRPF may be enabled at the Internet edge and at the internal access layer on the user-supporting Layer 3 interfaces. Starting in 12.(13)T, uRPF is also supported for IPv6.

For additional information about the configuration and use of uRPF, reference the Cisco Security Appliance Command Reference for ip verify reverse-path and the Understanding Unicast Reverse Path Forwarding Cisco Security Intelligence Operations white paper.

Identification: Spoofing Protection Using Unicast Reverse Path Forwarding

Firewall syslog message 106021 will be generated for packets denied by uRPF. 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 for 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 vulnerability 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

  Jul 12 2013 00:15:13: %ASA-1-106021: Deny UDP reverse path check from
         192.168.60.1 to 192.168.60.100 on interface outside
  Jul 12 2013 00:15:13: %ASA-1-106021: Deny UDP reverse path check from
         192.168.60.1 to 192.168.60.100 on interface outside
  Jul 12 2013 00:15:13: %ASA-1-106021: Deny UDP 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 uRPF 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, uRPF has dropped 11 IP packets received on interfaces with uRPF configured. Absence of output indicates that the uRPF 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.


Additional Information

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Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at 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.

Related Information

 
Alert History
 

Alert History

Initial Release


Product Sets
 
The security vulnerability applies to the following combinations of products.

Primary Products:
QNX Software Systems Ltd.QNX Neutrino RTOS 6.5.0 Base

Associated Products:
N/A




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