Cisco Applied Mitigation Bulletin

Identifying and Mitigating Exploitation of the Cisco ASA 5500 Series Adaptive Security Appliance Clientless VPN ActiveX Control Remote Code Execution Vulnerability

Advisory ID: cisco-amb-20120314-asaclient

http://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20120314-asaclient

Revision 1.0

For Public Release 2012 March 14 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 ASA 5500 Series Adaptive Security Appliance Clientless VPN ActiveX Control Remote Code Execution Vulnerability and provides identification and mitigation techniques that administrators can deploy on Cisco network devices.

Vulnerability Characteristics

The Cisco Clientless VPN Solution as deployed by Cisco Adaptive Security Appliances utilize an ActiveX control on client systems to perform port forwarding operations. If a Microsoft Windows based computer has been utilized to connect to a device running the Cisco Clientless VPN solution it may potentially be vulnerable. This vulnerability can be exploited remotely without authentication and requires user interaction. Successful exploitation of the vulnerability could allow arbitrary code execution. The attack vector for exploitation is through HTTP packets that typically use TCP port 80 but may also use TCP ports 3128, 8000, 8010, 8080, 8888, and 24326.

This vulnerability has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2012-0358.

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-20120314-asaclient 

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.

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 Application layer protocol inspection.

This protection mechanism filters and drops packets that are attempting to exploit this vulnerability.

Effective exploit prevention can also be provided by the Cisco ACE Application Control Engine Appliance and Module using Application protocol inspection.

This protection mechanism filters and drops packets that are attempting to exploit this vulnerability.

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.

Effective use of Cisco Intrusion Prevention System (IPS) event actions provides visibility into and protection against attacks that attempt to exploit this vulnerability.

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 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.

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 ASA, Cisco ASASM, and Cisco FWSM Firewalls

Mitigation: Application Layer Protocol Inspection

Application layer protocol inspection is available beginning in software release 7.2(1) for the Cisco ASA 5500 Series Adaptive Security Appliance, software release 8.5 for the Cisco Catalyst 6500 Series ASA Services Module, and in software release 4.0(1) for the Cisco Firewall Services Module. This advanced security feature performs deep packet inspection of traffic that transits the firewall. Administrators may construct an inspection policy for applications that require special handling through the configuration of inspection class maps and inspection policy maps, which are applied via a global or interface service policy.

Additional information about application layer protocol inspection is in the Configuring Application Layer Protocol Inspection section of the Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2 and the Configuring Application Inspection section of the Cisco Catalyst 6500 Series ASA Services Module CLI Configuration Guide, 8.5.

Caution: Application layer protocol inspection will decrease firewall performance. Administrators are advised to test performance impact in a lab environment before this feature is deployed in production environments.

HTTP Application Inspection
By using the HTTP inspection engine on the Cisco ASA 5500 Series Adaptive Security Appliances, Cisco 6500 Series ASA Services Modules, and the Cisco Firewall Services Module, administrators can configure regular expressions (regexes) for pattern matching and construct inspection class maps and inspection policy maps. These methods can help protect against specific vulnerabilities, such as the one described in this document, and other threats that may be associated with HTTP traffic. The following HTTP application inspection configuration uses the Cisco Modular Policy Framework (MPF) to create a policy for inspection of traffic on TCP ports 80, 3128, 8000, 8010, 8080, 8888, and 24326, which are the default ports for the Cisco IPS #WEBPORTS variable. The HTTP application inspection policy will drop connections where the HTTP response body contains the regex that is configured to match the ActiveX control that is associated with this vulnerability.

Caution: The configured regex can match text strings at any location in the body of an HTML response. Care should be taken to ensure that legitimate business applications that use matching text strings without calling the ActiveX control are not affected. Additional information about regex syntax is in Creating a Regular Expression.

Additional information about ActiveX exploits and mitigations that leverage Cisco firewall technologies is available in the Preventing ActiveX Exploits with Cisco Firewall Application Layer Protocol Inspection Cisco Security Intelligence Operations white paper.
!
!-- Configure a regex for the ActiveX class ID
!-- "B8E73359-3422-4384-8D27-4EA1B4C01232" that is
!-- associated with this vulnerability
!
regex CLSID_activeX "[Bb]8[Ee]73359[-]3422[-]4384[-]8[Dd]27 [-]4[Ee][Aa]1[Bb]4[Cc]01232" !
!-- Configure a regex class to match on the regular
!-- expression that is configured above
!
class-map type regex match-any vulnerable_activeX_class match regex CLSID_activeX !
!-- Configure an object group for the default ports that
!-- are used by the Cisco IPS #WEBPORTS variable, which
!-- are TCP ports 80 (www), 3128, 8000, 8010, 8080, 8888,
!-- and 24326
!
object-group service WEBPORTS tcp port-object eq www port-object eq 3128 port-object eq 8000 port-object eq 8010 port-object eq 8080 port-object eq 8888 port-object eq 24326 !
!-- Configure an access list that uses the WEBPORTS object
!-- group, which will be used to match TCP packets that
!-- are destined to the #WEBPORTS variable that is used
!-- by a Cisco IPS device
!
access-list Webports_ACL extended permit tcp any any object-group WEBPORTS !
!-- Configure a class that uses the above-configured
!-- access list to match TCP packets that are destined
!-- to the ports that are used by the Cisco IPS #WEBPORTS
!-- variable
!
class-map Webports_Class match access-list Webports_ACL !
!-- Configure an HTTP application inspection policy that
!-- identifies, drops, and logs connections that contain
!-- the regex that is configured above
!
policy-map type inspect http http_Policy
parameters
!
!-- "body-match-maximum" indicates the maximum number of
!-- characters in the body of an HTTP message that
!-- should be searched in a body match. The default value is
!-- 200 bytes. A large number such as that shown here may have
!-- an impact on system performance. Administrators are advised
!-- to test performance impact in a lab environment before
!-- this command is deployed in production environments
!
body-match-maximum 1380
match response body regex class vulnerable_activeX_class
drop-connection log
!
!-- Add the above-configured "Webports_Class" that matches
!-- TCP packets that are destined to the default ports
!-- that are used by the Cisco IPS #WEBPORTS variable to
!-- the default policy "global_policy" and use it to
!-- inspect HTTP traffic that transits the firewall
!
policy-map global_policy class Webports_Class inspect http http_Policy
!
!-- By default, the policy "global_policy" is applied
!-- globally, which results in the inspection of
!-- traffic that enters the firewall from all interfaces
!
service-policy global_policy global

For additional information about the configuration and use of object groups, reference the Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2 for Configuring Object Groups and the Configuring Objects and Access Lists section of the Cisco Catalyst 6500 Series ASA Services Module CLI Configuration Guide, 8.5.

Additional information about HTTP application inspection and the MPF is in the HTTP Inspection Overview section of the Cisco ASA 5500 Series Configuration Guide using the CLI, 8.2.

Identification: Application Layer Protocol Inspection

Firewall syslog message 415007 will be generated when an HTTP message body matches a user-defined regular expression. The syslog message will identify the corresponding HTTP class and HTTP policy and indicate the action applied to the HTTP connection. Additional information about this syslog message is in Cisco ASA 5500 Series System Log Message, 8.2 - 415007.

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 attempts to exploit this vulnerability. Administrators can 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.

HTTP Application Inspection

firewall#show logging | grep 415007
  Mar 14 2012 14:35:54: %ASA-5-415007: HTTP - matched Class 20: 
         vulnerable_activeX_class in policy-map http_Policy, Body matched - 
         Dropping connection from inside:192.168.60.85/2130 to 
         outside:192.0.2.63/80
  Mar 14 2012 14:35:55: %ASA-5-415007: HTTP - matched Class 20: 
         vulnerable_activeX_class in policy-map http_Policy, Body matched - 
         Dropping connection from inside:192.168.60.86/2133 to 
         outside:192.0.2.63/80
  Mar 14 2012 14:36:03: %ASA-5-415007: HTTP - matched Class 20:
         vulnerable_activeX_class in policy-map http_Policy, Body matched - 
         Dropping connection from inside:192.168.60.87/2129 to 
         outside:192.0.2.63/80

With HTTP application inspection enabled, the show service-policy inspect protocol command will identify the number of HTTP packets that are inspected and dropped by this feature. The following example shows output for show service-policy inspect http:

firewall# show service-policy inspect http
Global policy: 
  Service-policy: global_policy
    Class-map: inspection_default
    Class-map: Webports_Class
      Inspect: http http_Policy, packet 5025, drop 20, reset-drop 0
       protocol violations
          packet 0        
       match response body regex class vulnerable_activeX_class
drop-connection log, packet 20

In the preceding example, 5025 HTTP packets have been inspected and 20 HTTP packets have been dropped.

Cisco ACE

Mitigation: Application Protocol Inspection

Application protocol inspection is available for the Cisco ACE Application Control Engine Appliance and Module. This advanced security feature performs deep packet inspection of traffic that transits the Cisco ACE. Administrators can construct an inspection policy for applications that require special handling through the configuration of inspection class maps and inspection policy maps, which are applied via a global or interface service policy.

Additional information about application protocol inspection is in the Configuring Application Protocol Inspection section of the Cisco ACE 4700 Series Appliance Security Configuration Guide.

HTTP Deep Packet Inspection

To conduct HTTP deep packet inspection, administrators can configure regular expressions (regexes) for pattern matching and construct inspection class maps and inspection policy maps. These methods can help protect against specific vulnerabilities, such as the one described in this document, and other threats that may be associated with HTTP traffic. The following HTTP application protocol inspection configuration inspects traffic on TCP ports 80, 3128, 8000, 8010, 8080, 8888, and 24326, which are the default ports for the Cisco IPS #WEBPORTS variable. The HTTP application protocol inspection policy will drop connections where the HTTP content contains the regex that is configured to match the ActiveX control that is associated with this vulnerability.

Caution: The configured regex can match text strings at any location in the content of an HTML packet. Care should be taken to ensure that legitimate business applications that use matching text strings without calling the ActiveX control are not affected.

Additional information about ActiveX exploits and mitigations that leverage the Cisco ACE Application Control Engine Appliance and Module is available in the Preventing ActiveX Exploits with Cisco Application Control Engine Application Layer Protocol Inspection Cisco Security Intelligence Operations white paper.

!
!-- Configure an HTTP application inspection class that
!-- looks for HTTP packets that contain the regex for the
!-- ActiveX class ID "B8E73359-3422-4384-8D27-4EA1B4C01232"
!-- that is associated with this vulnerability
!
class-map type http inspect match-any vulnerable_activeX_http_class match content ".*[Bb]8[Ee]73359[-]3422[-]4384[-]8[Dd]27 [-]4[Ee][Aa]1[Bb]4[Cc]01232.*" !
!-- Configure an HTTP application inspection policy that
!-- identifies, resets, and logs connections that contain
!-- the regex that is configured above
!
policy-map type inspect http all-match http_Policy class vulnerable_activeX_http_class reset log !
!-- Configure an access list that matches TCP packets
!-- that are destined to the #WEBPORTS variable that is
!-- used by a Cisco IPS device
!
access-list WEBPORTS line 8 extended permit tcp any any eq www access-list WEBPORTS line 16 extended permit tcp any any eq 3128 access-list WEBPORTS line 24 extended permit tcp any any eq 8000 access-list WEBPORTS line 32 extended permit tcp any any eq 8010 access-list WEBPORTS line 40 extended permit tcp any any eq 8080 access-list WEBPORTS line 48 extended permit tcp any any eq 8888 access-list WEBPORTS line 56 extended permit tcp any any eq 24326 !
!-- Configure a Layer 4 class that uses the above-configured
!-- access list to match TCP packets that are destined
!-- to the ports that are used by the Cisco IPS #WEBPORTS
!-- variable
!
class-map match-all L4_http_class match access-list WEBPORTS !
!-- Configure a Layer 4 policy that applies the HTTP application
!-- inspection policy configured above to TCP packets that
!-- are destined to the ports that are used by the Cisco IPS
!-- #WEBPORTS variable
!
policy-map multi-match L4_http_Policy class L4_http_class inspect http policy http_Policy !
!-- Apply the configuration globally across all interfaces,
!-- which results in the inspection of all traffic that enters
!-- the ACE
!
service-policy input L4_http_Policy

Identification: Application Protocol Inspection

HTTP Deep Packet Inspection

ACE syslog message 415007 will be generated when an HTTP message body matches a user-defined regular expression. The syslog message will identify the corresponding HTTP class and HTTP policy and indicate the action applied to the HTTP connection. Additional information about this syslog message is in Cisco ACE 4700 Series Appliance System Message Guide - System Message 415007

ACE/Admin# show logging | include 415007
Mar 14 2012 14:26:43: %ACE-5-415007: HTTP - matched vulnerable_activeX_http_class
     in policy-map L4_http_Policy, Body matched - Resetting connection from 
     vlan206:192.168.60.63/1776 to vlan130:192.0.2.94/80 Connection 0x3a 
Mar 14 2012 14:30:33: %ACE-5-415007: HTTP - matched vulnerable_activeX_http_class 
     in policy-map L4_http_Policy, Body matched - Resetting connection from 
     vlan206:192.168.60.63/1778 to vlan130:192.0.2.94/80 Connection 0x3c 

When HTTP deep packet inspection is enabled, the show service-policy policyname detail command will identify the number of HTTP connections that are inspected and dropped by this feature. The following example shows output for show service-policy L4_http_Policy detail:

ACE/Admin# show service-policy L4_http_Policy detail

Status     : ACTIVE
Description: -----------------------------------------
Context Global Policy:
  service-policy: L4_http_Policy
    class: L4_http_class
      inspect http:
        L7 inspect policy : http_Policy
        Url Logging: DISABLED
        curr conns       : 0         , hit count        : 1         
        dropped conns    : 0         
        client pkt count : 3         , client byte count: 589                   
        server pkt count : 3         , server byte count: 547                   
        conn-rate-limit      : 0         , drop-count : 0         
        bandwidth-rate-limit : 0         , drop-count : 0         
        L4 policy stats:
Total Req/Resp: 12 , Total Allowed: 9
Total Dropped : 3 , Total Logged : 0
L7 Inspect policy : http_Policy
class/match : vulnerable_activeX_http_class
Inspect action :
reset log
Total Inspected : 12 , Total Matched: 3
Total Dropped OnError: 0

In the preceding example, 12 HTTP connections have been inspected and 3 HTTP connections have been dropped.

Additional information about HTTP deep packet inspection and application protocol inspection is in the Configuring Application Protocol Inspection section of the Cisco ACE 4700 Series Appliance Security Configuration Guide.

Cisco Intrusion Prevention System

Mitigation: Cisco IPS Signature Table

Administrators can use the Cisco IPS appliances and services modules to provide threat detection and help prevent attempts to exploit the vulnerability described in this document. The following table provides an overview of the CVE identifier and the respective Cisco IPS signature that will trigger events on potential attempts to exploit this vulnerability.

CVE ID Signature Release Signature ID Signature Name Enabled Severity Fidelity*
CVE-2012-0358 S632 41026/0 Cisco Port Forwarder ActiveX Control Buffer Overflow Yes High 90

* Fidelity is also referred to as Signature Fidelity Rating (SFR) and is the relative measure of the accuracy of the signature (predefined). The value ranges from 0 through 100 and is set by Cisco Systems, Inc.

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 listed in the preceding table.

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 7.x and 6.x 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.

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 Cisco IPS devices and provides the Event Viewer, which can query for events that are related to the vulnerability that is described in this document.

Using the IPS Alert Events predefined view in the Event Viewer, the user can enter the search string 41026/0 in the event filter to return all captured events related to Cisco IPS signature 41026/0.

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 vulnerability that is described in this document:

  • ASA-4-415007 (HTTP inspection)

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

Cisco Security Manager Report Manager

Beginning in software version 4.1, Cisco Security Manager supports the Report Manager, the Cisco IPS event reporting feature. This feature allows an administrator to define reports based on Cisco IPS events of interest. Reports can be scheduled or users can run ad hoc reports as required.

Using the Report Manager, the user can define an IPS Top Signatures report for Cisco IPS devices of interest based on time-range and signature characteristics. When the Signature ID is set to 41026/0, Cisco Security Manager will generate a comprehensive report that ranks the count of the alerts fired for the signature of interest compared to the total sum of all signature alerts shown in the report.

For more information about Cisco Security Manager IPS Event Reporting refer to the Understanding IPS Top Reports 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 vulnerability that is described in this document. The queries can be made by Sig ID and Syslog ID as shown in the following list:

  • 41026/0 Cisco Port Forwarder ActiveX Control Buffer Overflow
  • ASA-4-415007 (HTTP inspection)

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-MARCH-14 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.

Related Information


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