Advisory ID: cisco-amb-20080625-waas
http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20080625-waas
Revision 1.1
For Public Release 2008 June 25 16:00 UTC (GMT)
Contents
Cisco ResponseDevice-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 Response Wide Area Application Services (WAAS) Common UNIX Printing System (CUPS) Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
Vulnerability Characteristics
The Cisco Wide Area Application Services contains a vulnerability when it processes specially crafted Internet Printing Protocol (IPP) packets. This vulnerability can be exploited remotely without authentication and without end-user interaction. Successful exploitation of this vulnerability may allow arbitrary code execution or 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 IPP packets using TCP port 631.
This vulnerability has been assigned CVE identifier CVE-2007-4351.
Vulnerable, non-affected and fixed software information is available in the PSIRT Security Response: http://tools.cisco.com/security/center/content/CiscoSecurityResponse/cisco-sr-20080625-waas.
Mitigation Technique Overview
Cisco devices provide several countermeasures for this vulnerability. Administrators are advised to consider these protection methods to be general security best practices for infrastructure devices and the traffic that transits the network. This section of the document provides an overview of these techniques.
Cisco IOS Software can provide effective means of exploit prevention using transit access control lists (tACLs). This protection mechanism filters and drops packets that are attempting to exploit the vulnerability that has a network attack vector.
Effective 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 transit access control lists (tACLs). This protection mechanism filters and drops packets that are attempting to exploit the vulnerability that has a network attack vector.
Cisco IOS NetFlow can provide visibility into network-based exploitation attempts using flow records.
Cisco IOS Software, Cisco ASA, Cisco PIX security appliances, and FWSM firewalls can provide visibility through syslog messages and the 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 [this vulnerability|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 the vulnerability that has a network attack vector when the attack comes from a trusted source address.
The tACL policy denies unauthorized IPP packets on TCP port 631 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 available in Transit Access Control Lists: Filtering at Your Edge.
!-- Include any explicit permit statements for trusted sources !-- that require access on the vulnerable port ! access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 631 ! !-- The following vulnerability-specific access control entry !-- (ACE) can aid in identification of attacks ! access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 631 ! !-- Permit/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 undesirable 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.
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 IPP packets on TCP port 631 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 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 631
20 deny tcp any 192.168.60.0 0.0.0.255 eq 631 (122 matches)
30 deny ip any any
router#
In the preceding example, access list 150 has dropped 122 IPP packets on TCP port 631 for 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 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: 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.
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 the vulnerability described in this document that has a network attack vector. 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 (506 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.324 .673 .000 .000 .001 .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
94 active, 4002 inactive, 96 added
928 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
IP Sub Flow Cache, 25800 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-Telnet 1 0.0 3 60 0.0 8.9 15.6
ICMP 1 0.0 1 138 0.0 0.0 15.1
Total: 2 0.0 2 79 0.0 4.4 15.3
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Et0/0 192.168.46.4 Et0/1 192.168.10.205 06 A607 B586 1
Et0/0 192.168.236.84 Et0/1 192.168.60.3 06 610F 0277 15
Et0/0 192.168.126.252 Et0/1 192.168.107.94 06 831E D20C 5
Et0/0 192.168.205.221 Et0/1 192.168.179.38 11 24F5 98D6 5
Et0/0 192.168.233.30 Et0/1 192.168.121.133 06 6BAC 3AF4 4
Et0/0 192.168.125.221 Et0/1 192.168.137.242 11 25C5 174D 4
Et0/0 192.168.240.172 Et0/1 192.168.60.127 06 C51B 0277 1
Et0/0 192.168.164.176 Et0/1 192.168.38.20 11 DE48 D9A9 5
Et0/0 192.168.155.178 Et0/1 192.168.86.254 11 0CBE 1B97 3
Et0/0 192.168.184.14 Et0/1 192.168.15.182 06 BC0D 06BB 1
Et0/0 192.168.167.200 Et0/1 192.168.60.73 06 1B1F 0277 4
Et0/0 192.168.131.158 Et0/1 192.168.60.131 06 7366 0277 3
Et0/0 192.168.38.164 Et0/1 192.168.54.227 11 D075 8BBD 4
Et0/0 192.168.129.110 Et0/1 192.168.60.100 06 161E 0277 2
Et0/0 192.168.241.22 Et0/1 192.168.47.58 11 38CD EEB9 6
Et0/0 192.168.239.196 Et0/1 192.168.108.177 06 25B9 79FD 2
Et0/0 192.168.193.100 Et0/1 192.168.251.88 11 58AF BBE9 4
Et0/0 192.168.37.102 Et0/1 192.168.60.144 06 F8BC 0277 11
router#
In the preceding example, there are multiple flows for IPP on TCP port 631 (hex value 0277). Administrators are advised to compare these flows to baseline utilization for IPP traffic sent on TCP port 631 and also investigate the flows to determine whether they are sourced from untrusted hosts or networks.
To view only the traffic flows for IPP packets on TCP port 631 (hex value 0277) use the command show ip cache flow | include SrcIf|_06_.*0277 as shown here:
router#show ip cache flow | include SrcIf|_06_.*0277 SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Et0/0 192.168.236.84 Et0/1 192.168.60.3 06 610F 0277 15 Et0/0 192.168.240.172 Et0/1 192.168.60.127 06 C51B 0277 1 Et0/0 192.168.167.200 Et0/1 192.168.60.73 06 1B1F 0277 4 Et0/0 192.168.131.158 Et0/1 192.168.60.131 06 7366 0277 3 Et0/0 192.168.129.110 Et0/1 192.168.60.100 06 161E 0277 2 Et0/0 192.168.37.102 Et0/1 192.168.60.144 06 F8BC 0277 11 Et0/0 192.168.150.34 Et0/1 192.168.60.50 06 F85E 0277 10 Et0/0 192.168.74.86 Et0/1 192.168.60.93 06 9B1E 0277 2 Et0/0 192.168.91.247 Et0/1 192.168.60.58 06 FCB9 0277 4 Et0/0 192.168.62.97 Et0/1 192.168.60.109 06 5629 0277 1 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 the vulnerability that has a network attack vector when the attack comes from a trusted source address.
The tACL policy denies unauthorized IPP packets on TCP port 631 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 available in Transit Access Control Lists: Filtering at Your Edge.
! !-- Include any explicit permit statements for trusted sources !-- requiring access on the vulnerable port ! access-list Transit-ACL-Policy extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 631 ! !-- The following vulnerability-specific access control entry !-- (ACE) can aid in identification of attacks ! access-list Transit-ACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 631 ! !-- Permit/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 Transit-ACL-Policy extended deny ip any any ! !-- Apply tACL to interface(s) in the ingress direction ! access-group Transit-ACL-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 IPP packets on TCP port 631 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 Transit-ACL-Policy follows:
firewall#show access-list Transit-ACL-Policy access-list Transit-ACL-Policy; 3 elements access-list Transit-ACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 631 (hitcnt=6) access-list Transit-ACL-Policy line 2 extended deny tcp any 192.168.60.0 255.255.255.0 eq 631 (hitcnt=247) access-list Transit-ACL-Policy line 3 extended deny ip any any (hitcnt=8) firewall#
In the preceding example, access list Transit-ACL-Policy has dropped 247 IPP packets on TCP port 631 received from an untrusted host or network. In addition, syslog message 106023 can provide valuable information, including 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 available 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 available in Configuring Logging on the Cisco Security Appliance. Information about configuring syslog on the FWSM for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers is available in Configuring Monitoring and Logging on the Cisco FWSM.
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 described in this document that has a network attack vector. 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 available in Using the Command Line Interface.
firewall#show logging | grep 106023 May 14 2008 16:35:31: %ASA-4-106023: Deny tcp src outside:192.168.93.163/57540 dst inside:192.168.60.112/631 by access-group "Transit-ACL-Policy" May 14 2008 17:18:33: %ASA-4-106023: Deny tcp src outside:192.168.231.104/54464 dst inside:192.168.60.80/631 by access-group "Transit-ACL-Policy" May 15 2008 08:43:38: %ASA-4-106023: Deny tcp src outside:192.168.64.107/41986 dst inside:192.168.60.165/631 by access-group "Transit-ACL-Policy" May 15 2008 23:38:00: %ASA-4-106023: Deny tcp src outside:192.168.32.58/21773 dst inside:192.168.60.85/631 by access-group "Transit-ACL-Policy" May 16 2008 23:58:54: %ASA-4-106023: Deny tcp src outside:192.168.39.232/22075 dst inside:192.168.60.67/631 by access-group "Transit-ACL-Policy" May 17 2008 08:35:56: %ASA-4-106023: Deny tcp src outside:192.168.151.82/40832 dst inside:192.168.60.230/631 by access-group "Transit-ACL-Policy" May 17 2008 13:46:34: %ASA-4-106023: Deny tcp src outside:192.168.17.169/27307 dst inside:192.168.60.241/631 by access-group "Transit-ACL-Policy" May 18 2008 02:44:54: %ASA-4-106023: Deny tcp src outside:192.168.61.234/53863 dst inside:192.168.60.214/631 by access-group "Transit-ACL-Policy" firewall#
In the preceding example, the messages logged for the tACL Transit-ACL-Policy show IPP packets for TCP port 631 sent to the address block assigned to the infrastructure devices.
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 1.1 |
2008-August-19 |
Corrected link in Vulnerability Overview section |
|
Revision 1.0 |
2008-June-25 |
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/en/US/products/products_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
- Cisco Applied Mitigation Bulletins
- Cisco Security Center
- Transit Access Control Lists: Filtering at Your Edge
- Cisco IOS NetFlow - Home Page on Cisco.com
- Cisco IOS NetFlow White Papers
- Cisco Network Foundation Protection White Papers
- Cisco Network Foundation Protection Presentations
- Understanding Access Control List Logging
- Embedded Event Manager in a Security Context
- Identifying Incidents Using Firewall and IOS Router Syslog Events
- A Security-Oriented Approach to IP Addressing
- Cisco Firewall Products - Home Page on Cisco.com
- Common Vulnerabilities and Exposures (CVE)
