This Applied Mitigation Bulletin is a companion document to the PSIRT Security Advisory CiscoWorks Common Services Arbitrary Code Execution Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.
Cisco Common Services for CiscoWorks contains a vulnerability when it processes a malformed packet. This vulnerability can be exploited remotely without authentication, and without end user interaction. Successful exploitation of this vulnerability may allow arbitrary code execution, or may cause the affected device to crash. The attack vector for exploitation is through packets using TCP port 443 and TCP port 1741 when the default configuration is used.
This vulnerability has been assigned CVE identifier CVE-2010-3036.
Information about vulnerable, unaffected, and fixed software is available in the PSIRT Security Advisory, which is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20101027-cs.
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 this vulnerability.
Effective exploit prevention can also be provided by the Cisco ASA 5500 Series Adaptive Security Appliance and the Firewall Services Module (FWSM) for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers using tACLs.
This protection mechanism filters and drops packets that are attempting to exploit this vulnerability.
Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit this vulnerability.
Cisco IOS NetFlow records can provide visibility into network-based exploitation attempts.
Cisco IOS Software, Cisco ASA, 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 Monitoring, Analysis, and Response System (Cisco Security MARS) appliance can also provide visibility through incidents, queries, and event reporting.
Organizations are advised to follow their standard risk evaluation and mitigation processes to determine the potential impact of this vulnerability. Triage refers to sorting projects and prioritizing efforts that are most likely to be successful. Cisco has provided documents that can help organizations develop a risk-based triage capability for their information security teams. Risk Triage for Security Vulnerability Announcements and Risk Triage and Prototyping can help organizations develop repeatable security evaluation and response processes.
Caution: The effectiveness of any mitigation technique depends on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. As with any configuration change, evaluate the impact of this configuration prior to applying the change.
Specific information about mitigation and identification is available for these devices:
To protect the network from traffic that enters the network at ingress access points, which may include Internet connection points, partner and supplier connection points, or VPN connection points, administrators are advised to deploy transit access control lists (tACLs) to perform policy enforcement. Administrators can construct a tACL by explicitly permitting only authorized traffic to enter the network at ingress access points or permitting authorized traffic to transit the network in accordance with existing security policies and configurations. A tACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The tACL policy denies unauthorized packets on the default ports, TCP port 443 and TCP port 1741, that are sent to affected devices. In the following example, 192.168.60.0/24 is the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.
Additional information about tACLs is in Transit Access Control Lists: Filtering at Your Edge.
!-- Include explicit permit statements for trusted sources !-- that require access on the vulnerable ports ! access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 443 access-list 150 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 1741 ! !-- 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 443 access-list 150 deny tcp any 192.168.60.0 0.0.0.255 eq 1741 ! !-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance !-- with existing security policies and configurations ! !-- Explicit deny for all other IP traffic ! access-list 150 deny ip any any ! !-- Apply tACL to interfaces in the ingress direction ! interface GigabitEthernet0/0 ip access-group 150 in
Note that filtering with an interface access list will elicit the transmission of ICMP unreachable messages back to the source of the filtered traffic. Generating these messages could have the undesired effect of increasing CPU utilization on the device. In Cisco IOS Software, ICMP unreachable generation is limited to one packet every 500 milliseconds by default. ICMP unreachable message generation can be disabled using the interface configuration command no ip unreachables. ICMP unreachable rate limiting can be changed from the default using the global configuration command ip icmp rate-limit unreachable interval-in-ms.
After the administrator applies the tACL to an interface, the show ip access-lists command will identify the number of packets on TCP port 443 and TCP port 1741 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 443
20 permit tcp host 192.168.100.1 192.168.60.0 0.0.0.255 eq 1741
30 deny tcp any 192.168.60.0 0.0.0.255 eq 443 (12 matches)
40 deny tcp any 192.168.60.0 0.0.0.255 eq 1741 (26 matches)
50 deny ip any any
router#
In the preceding example, access list 150 has dropped the following packets that are received from an untrusted host or network:
For additional information about investigating incidents using ACE counters and syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.
Administrators can use Embedded Event Manager to provide instrumentation when specific conditions are met, such as ACE counter hits. The Applied Intelligence white paper Embedded Event Manager in a Security Context provides additional details about how to use this feature.
The log and log-input access control list (ACL) option will cause packets that match specific ACEs to be logged. The log-input option enables logging of the ingress interface in addition to the packet source and destination IP addresses and ports.
Caution: Access control list logging can be very CPU intensive and must be used with extreme caution. Factors that drive the CPU impact of ACL logging are log generation, log transmission, and process switching to forward packets that match log-enabled ACEs.
For Cisco IOS Software, the ip access-list logging interval interval-in-ms command can limit the effects of process switching induced by ACL logging. The logging rate-limit rate-per-second [except loglevel] command limits the impact of log generation and transmission.
The CPU impact from ACL logging can be addressed in hardware on the Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers with Supervisor Engine 720 or Supervisor Engine 32 using optimized ACL logging.
For additional information about the configuration and use of ACL logging, reference the Understanding Access Control List Logging Applied Intelligence white paper.
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. 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 (17258967 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.013 .225 .422 .155 .035 .008 .005 .004 .002 .001 .014 .002 .002 .003 .001
512 544 576 1024 1536 2048 2560 3072 3584 4096 4608
.000 .000 .045 .017 .034 .000 .000 .000 .000 .000 .000
IP Flow Switching Cache, 4456704 bytes
18 active, 65518 inactive, 2445817 added
226043591 ager polls, 0 flow alloc failures
Active flows timeout in 2 minutes
Inactive flows timeout in 60 seconds
IP Sub Flow Cache, 533256 bytes
0 active, 16384 inactive, 0 added, 0 added to flow
0 alloc failures, 0 force free
1 chunk, 1 chunk added
last clearing of statistics never
Protocol Total Flows Packets Bytes Packets Active(Sec) Idle(Sec)
-------- Flows /Sec /Flow /Pkt /Sec /Flow /Flow
TCP-Telnet 653 0.0 77 40 0.0 27.4 24.0
TCP-FTP 765 0.0 15 42 0.0 1.3 25.8
TCP-FTPD 3 0.0 324 608 0.0 1.9 42.9
TCP-WWW 43844 0.0 20 456 0.2 9.3 40.0
TCP-SMTP 4973 0.0 6 59 0.0 35.3 59.7
TCP-X 2 0.0 1 52 0.0 0.0 66.8
TCP-BGP 2 0.0 1 52 0.0 0.0 63.7
TCP-NNTP 2 0.0 1 52 0.0 0.0 88.7
TCP-other 276300 0.0 19 267 1.2 29.1 41.8
UDP-DNS 236963 0.0 2 69 0.1 8.8 57.8
UDP-NTP 31121 0.0 1 75 0.0 0.2 60.3
UDP-TFTP 9 0.0 4 80 0.0 27.6 55.7
UDP-other 485427 0.1 8 106 0.9 21.6 56.4
ICMP 642287 0.1 2 83 0.3 10.6 60.0
IGMP 265863 0.0 2 37 0.1 53.9 42.7
IP-other 457584 0.1 8 92 0.9 94.0 16.3
Total: 2445798 0.5 7 167 4.0 34.9 46.6
SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts
Gi0/0 192.168.137.50 Gi0/1 192.168.60.42 11 0984 00A1 1
Gi0/0 192.168.211.3 Gi0/1 192.168.60.101 11 0911 00A1 3
Gi0/0 192.168.18.79 Gi0/1 192.168.60.105 06 1C16 06CD 4
Gi0/0 192.168.203.49 Gi0/1 192.168.60.67 11 0B3E 00A1 5
Gi0/0 192.168.101.251 Gi0/1 192.168.60.103 06 3A89 01BB 1
Gi0/0 192.168.122.5 Gi0/1 192.168.60.29 11 0BD7 00A1 1
Gi0/0 192.168.40.131 Gi0/1 192.168.60.80 06 22FC 01BB 7
router#
In the preceding example, there are multiple flows on TCP port 443 (hex value 01BB) and TCP port 1741 (hex value 06CD).
To view only the traffic flows for packets on TCP port 443 (hex value 01BB) and TCP port 1741 (hex value 06CD), the command show ip cache flow | include SrcIf|_06_.*(01BB|06CD)_will display the related TCP NetFlow records as shown here:
TCP Flows
router#show ip cache flow | include SrcIf|_06_.*(01BB|06CD)_ SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts Gi0/0 192.168.18.79 Gi0/1 192.168.60.105 06 1C16 06CD 4 Gi0/0 192.168.101.251 Gi0/1 192.168.60.103 06 3A89 01BB 1 Gi0/0 192.168.40.131 Gi0/1 192.168.60.80 06 22FC 01BB 7 router#
To protect the network from traffic that enters the network at ingress access points, which may include Internet connection points, partner and supplier connection points, or VPN connection points, administrators are advised to deploy tACLs to perform policy enforcement. Administrators can construct a tACL by explicitly permitting only authorized traffic to enter the network at ingress access points or permitting authorized traffic to transit the network in accordance with existing security policies and configurations. A tACL workaround cannot provide complete protection against this vulnerability when the attack originates from a trusted source address.
The tACL policy denies unauthorized packets on the default ports, TCP port 443 and TCP port 1741, that are sent to affected devices. In the following example, 192.168.60.0/24 is the IP address space that is used by the affected devices, and the host at 192.168.100.1 is considered a trusted source that requires access to the affected devices. Care should be taken to allow required traffic for routing and administrative access prior to denying all unauthorized traffic.
Additional information about tACLs is in Transit Access Control Lists: Filtering at Your Edge.
!
!-- Include explicit permit statements for trusted sources
!-- that require access on the vulnerable ports
!
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq https
access-list tACL-Policy extended permit tcp host 192.168.100.1
192.168.60.0 255.255.255.0 eq 1741
!
!-- 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 https
access-list tACL-Policy extended deny tcp any 192.168.60.0 255.255.255.0 eq 1741
!
!-- Permit or deny all other Layer 3 and Layer 4 traffic in accordance
!-- with existing security policies and configurations
!
!-- Explicit deny for all other IP traffic
!
access-list tACL-Policy extended deny ip any any
!
!-- Apply tACL to interface(s) in the ingress direction
!
access-group tACL-Policy in interface outside
After the tACL has been applied to an interface, administrators can use the show access-list command to identify the number of packets on TCP port 443 and TCP port 1741 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 follows:
firewall#show access-list tACL-Policy access-list tACL-Policy; 5 elements access-list tACL-Policy line 1 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq https (hitcnt=0) access-list tACL-Policy line 2 extended permit tcp host 192.168.100.1 192.168.60.0 255.255.255.0 eq 1741 (hitcnt=0) access-list tACL-Policy line 3 extended deny tcp any 192.168.60.0 255.255.255.0 eq https (hitcnt=15) access-list tACL-Policy line 4 extended deny tcp any 192.168.60.0 255.255.255.0 eq 1741 (hitcnt=7) access-list tACL-Policy line 5 extended deny ip any any (hitcnt=0)
In the preceding example, access list tACL-Policy has dropped the following packets received from an untrusted host or network:
Firewall syslog message 106023 will be generated for packets denied by an access control entry (ACE) that does not have the log keyword present. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 106023.
Information about configuring syslog for the Cisco ASA 5500 Series Adaptive Security Appliance is in Monitoring - Configuring Logging. Information about configuring syslog on the FWSM for Cisco Catalyst 6500 Series switches and Cisco 7600 Series routers is in Monitoring the Firewall Services Module.
In the following example, the show logging | grep regex command extracts syslog messages from the logging buffer on the firewall. These messages provide additional information about denied packets that could indicate potential attempts to exploit the 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
Oct 21 2010 00:07:23: %ASA-4-106023: Deny tcp src outside:192.0.2.101/3710
dst inside:192.168.60.112/1741 by access-group "tACL-Policy"
Oct 21 2010 00:07:24: %ASA-4-106023: Deny tcp src outside:192.0.2.98/3711
dst inside:192.168.60.27/443 by access-group "tACL-Policy"
Oct 21 2010 00:07:24: %ASA-4-106023: Deny tcp src outside:192.0.2.149/3712
dst inside:192.168.60.48/1741 by access-group "tACL-Policy"
Oct 21 2010 00:07:24: %ASA-4-106023: Deny tcp src outside:192.0.2.172/3713
dst inside:192.168.60.131/1741 by access-group "tACL-Policy"
Oct 21 2010 00:07:24: %ASA-4-106023: Deny tcp src outside:192.0.2.129/3714
dst inside:192.168.60.231/443 by access-group "tACL-Policy"
firewall#
In the preceding example, the messages logged for the tACL tACL-Policy show packets for TCP port 443 and TCP port 1741 sent to the address block assigned to affected devices.
Additional information about syslog messages for ASA security appliances is in Cisco ASA 5500 Series System Log Messages, 8.2. Additional information about syslog messages for the FWSM is in Catalyst 6500 Series Switch and Cisco 7600 Series Router Firewall Services Module Logging System Log Messages.
For additional information about investigating incidents using syslog events, reference the Identifying Incidents Using Firewall and IOS Router Syslog Events Applied Intelligence white paper.
Administrators can use Cisco Intrusion Prevention System (IPS) appliances and services modules to provide threat detection and help prevent attempts to exploit the vulnerability that is described in this document. Beginning with signature update S524 for sensors running Cisco IPS version 6.x and greater, the vulnerability can be detected by signature 30859/0 (Signature Name: CiscoWorks Common Services Arbitrary Code Execution Vulnerability). Signature 30859/0 is enabled by default, triggers a High severity event, has a signature fidelity rating (SFR) of 85, and is configured with a default event action of produce-alert.
Signature 30859/0 fires when a single packet sent using TCP port 1741 is detected. Firing of this signature may indicate a potential exploit of the vulnerability.
Administrators can configure Cisco IPS sensors to perform an event action when an attack is detected. The configured event action performs preventive or deterrent controls to help protect against an attack that is attempting to exploit the vulnerability that is described in this document.
Cisco IPS sensors are most effective when deployed in inline protection mode combined with the use of an event action. Automatic Threat Prevention for Cisco IPS 6.x and greater sensors that are deployed in inline protection mode provides threat prevention against an attack that is attempting to exploit the vulnerability that is described in this document. Threat prevention is achieved through a default override that performs an event action for triggered signatures with a riskRatingValue greater than 90.
For additional information about the risk rating and threat rating calculation, reference Risk Rating and Threat Rating: Simplify IPS Policy Management.
The Cisco Security Monitoring, Analysis, and Response System (Cisco Security MARS) appliance can create incidents regarding events that are related to the vulnerability that is described in this document using IPS signature 30859/0 (Signature Name: CiscoWorks Common Services Arbitrary Code Execution Vulnerability). After the S524 dynamic signature update has been downloaded, using keyword NR-30859/0 for IPS signature 30859/0 and a query type of All Matching Events on the Cisco Security MARS appliance will provide a report that lists the incidents created by the IPS signature.
Beginning with the 4.3.1 and 5.3.1 releases of Cisco Security MARS appliances, support for the Cisco IPS dynamic signature updates feature has been added. This feature downloads new signatures from Cisco.com or from a local web server, correctly processes and categorizes received events that match those signatures, and includes them in inspection rules and reports. These updates provide event normalization and event group mapping, and they also enable the MARS appliance to parse new signatures from the IPS devices.
Caution: If dynamic signature updates are not configured, events that match these new signatures appear as unknown event type in queries and reports. Because MARS will not include these events in inspection rules, incidents may not be created for potential threats or attacks that occur within the network.
By default, this feature is enabled but requires configuration. If it is not configured, the following Cisco Security MARS rule will be triggered:
System Rule: CS-MARS IPS Signature Update Failure
When this feature is enabled and configured, administrators can determine the current signature version downloaded by MARS by selecting Help > About and reviewing the IPS Signature Version value.
Additional information about dynamic signature updates and instructions for configuring dynamic signature updates are available for the Cisco Security MARS 4.3.1 and 5.3.1 releases.
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Revision 1.0 |
2010-October-27 |
Initial public release |
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