‘Cisco ASA 5500 Series Adaptive Security Appliances Multiple Vulnerabilities’

Summary

Cisco ASA 5500 Series Adaptive Security Appliances are affected by multiple vulnerabilities. Affected versions of Cisco ASA Software vary depending on the specific vulnerability.’

Credit:

‘The original article can be found at: http://www.cisco.com/warp/public/707/cisco-sa-20100217-asa.shtml


Details

Vulnerable Systems:
 * Cisco ASA 5500 Series Adaptive Security Appliances

To determine whether a vulnerable version of Cisco ASA Software is running on an appliance, administrators can issue the ‘show version’ command-line interface (CLI) command. The following example shows a Cisco ASA 5500 Series Adaptive Security Appliance that is running software version 8.0(4):

ASA#show version
Cisco Adaptive Security Appliance Software Version 8.0(4)
Device Manager Version 6.0(1)
    <output truncated>

Customers who use Cisco ASDM to manage devices can locate the software version in the table that is displayed in the login window or upper-left corner of the Cisco ASDM window.

The Cisco Firewall Services Module (FWSM) is affected by some of the vulnerabilities in this advisory. A separate Cisco Security Advisory has been published to disclose the vulnerabilities that affect the FWSM. This advisory is available at
http://www.cisco.com/warp/public/707/cisco-sa-20100217-fwsm.shtml.

Cisco ASA 5500 Series Adaptive Security Appliances are affected by the following vulnerabilities:

* TCP Connection Exhaustion Denial of Service Vulnerability
* Session Initiation Protocol (SIP) Inspection Denial of Service Vulnerabilities
* Skinny Client Control Protocol (SCCP) Inspection Denial of Service Vulnerability
* WebVPN Datagram Transport Layer Security (DTLS) Denial of Service Vulnerability
* Crafted TCP Segment Denial of Service Vulnerability
* Crafted Internet Key Exchange (IKE) Message Denial of Service Vulnerability
* NT LAN Manager version 1 (NTLMv1) Authentication Bypass Vulnerability

These vulnerabilities are not interdependent; a release that is affected by one vulnerability is not necessarily affected by the others.

TCP Connection Exhaustion Denial of Service Vulnerability
+——————————————————–

Cisco ASA 5500 Series Adaptive Security Appliances may experience a TCP connection exhaustion condition (no new TCP connections are accepted) that can be triggered through the receipt of specific TCP segments during the TCP connection termination phase. Appliances that are running versions 7.1.x, 7.2.x, 8.0.x, 8.1.x, and 8.2.x are affected when they are configured for any of the following features:

* SSL VPNs
* Cisco Adaptive Security Device Manager (ASDM) Administrative Access
* Telnet Access
* SSH Access
* Virtual Telnet
* Virtual HTTP
* Transport Layer Security (TLS) Proxy for Encrypted Voice Inspection

SIP Inspection Denial of Service Vulnerabilities
+———————————————–

Two denial of service (DoS) vulnerabilities affect the SIP inspection feature of Cisco ASA 5500 Series Adaptive Security Appliances. Versions 7.0.x, 7.1.x, 7.2.x, 8.0.x, 8.1.x, and 8.2.x are affected. SIP inspection is enabled by default.

To check if SIP inspection is enabled, issue the ‘show service-policy | include sip’ command and confirm that some output is returned. Sample output is displayed in the following example:

ciscoasa#show service-policy | include sip
Inspect: sip , packet 0, drop 0, reset-drop 0

Alternatively, an appliance that has SIP inspection enabled has a configuration similar to the following:

class-map inspection_default
match default-inspection-traffic
!
policy-map global_policy
class inspection_default

inspect sip

!
service-policy global_policy global

SCCP Inspection Denial of Service Vulnerability
+———————————————-

A denial of service vulnerability affects the SCCP inspection feature of the Cisco ASA 5500 Series Adaptive Security Appliances. Versions 8.0.x, 8.1.x, and 8.2.x are affected. SCCP inspection is enabled by default.

To check if SCCP inspection is enabled, issue the ‘show service-policy | include skinny’ command and confirm that some output is returned. Sample output is displayed in the following example:

ciscoasa#show service-policy | include skinny
Inspect: skinny , packet 0, drop 0, reset-drop 0

Alternatively, an appliance that has SCCP inspection enabled has a configuration similar to the following:

class-map inspection_default
match default-inspection-traffic
!
policy-map global_policy
class inspection_default

inspect skinny

!
service-policy global_policy global

WebVPN DTLS Denial of Service Vulnerability
+——————————————

Cisco ASA 5500 Series Adaptive Security Appliances are affected by a denial of service vulnerability that exists when WebVPN and DTLS are enabled. Affected versions include 7.1.x, 7.2.x, 8.0.x, 8.1.x, and 8.2.x. Administrators can enable WebVPN with the ‘enable ‘ command in ‘webvpn’ configuration mode. DTLS can be enabled by issuing the ‘svc dtls enable’ command in ‘group policy webvpn’ configuration mode. The following configuration snippet provides an example of a WebVPN configuration that enables DTLS:

webvpn
enable outside
svc enable

!
group-policy internal
group-policy attributes

webvpn
svc dtls enable

Altough WebVPN is disabled by default, DTLS is enabled by default in recent software releases.

Crafted TCP Segment Denial of Service Vulnerability
+————————————————–

Cisco ASA 5500 Series Adaptive Security Appliances are affected by a denial of service vulnerability that can be triggered by a malformed TCP segment that transits the appliance. This vulnerability only affects configurations that use the ‘nailed’ option at the end of their static statement. Additionally, traffic that matches ‘static’ statement must also be inspected by a Cisco AIP-SSM (an Intrusion Prevention System (IPS) module) in inline mode. IPS inline operation mode is enabled by using the ‘ips inline {fail-close | fail-open}’ command in ‘class’ configuration mode. Cisco ASA 5500 Series Adaptive Security Appliances that are running software versions 7.0.x, 7.1.x, 7.2.x, 8.0.x, 8.1.x, and 8.2.x are affected.

Crafted IKE Message Denial of Service Vulnerability
+————————————————–

A crafted IKE message that is sent through an IPsec tunnel that terminates on a Cisco ASA 5500 Series Adaptive Security Appliance could cause all IPsec tunnels that terminate on the same device to be torn down. Versions 7.0.x, 7.1.x, 7.2.x, 8.0.x, 8.1.x, and 8.2.x are affected. IKE is not enabled by default. If IKE is enabled, the ‘isakmp enable ‘ command appears in the configuration.

NTLMv1 Authentication Bypass Vulnerability
+—————————————–

An authentication bypass vulnerability affects Cisco ASA 5500 Series Adaptive Security Appliances when NTLMv1 authentication is configured. Versions 7.0.x, 7.1.x, 7.2.x, 8.0.x, 8.1.x, and 8.2.x are affected. Administrators can configure NTLMv1 authentication by defining an Authentication, Authorization, and Accounting (AAA) server group that uses the NTLMv1 protocol with the ‘aaa-server protocol nt’ command and then configuring a service that requires authentication to use that AAA server group. To verify that NTLMv1 authentication is enabled and active, issue the ‘show aaa-server protocol nt’ command. Sample output is displayed in the following example:

ciscoasa#show aaa-server protocol nt
Server Group: test
Server Protocol: nt
Server Address: 192.168.10.11
Server port: 139
Server status: ACTIVE, Last transaction (success) at 11:10:08 UTC Fri Jan 29

Cisco PIX 500 Series Security Appliance Vulnerability Status
+———————————————————–

Cisco PIX 500 Series Security Appliances are affected by the following vulnerabilities:

* TCP Connection Exhaustion Denial of Service Vulnerability
* SIP Inspection Denial of Service Vulnerabilities
* SCCP Inspection Denial of Service Vulnerability
* Crafted IKE Message Denial of Service Vulnerability
* NTLMv1 Authentication Bypass Vulnerability

Because the Cisco PIX 500 Series Security Appliances reached End of Software Maintenance Releases on July 28, 2009, no further software releases will be available for the Cisco PIX 500 Series Security Appliances. Cisco PIX 500 Series Security Appliances customers are encouraged to migrate to Cisco ASA 5500 Series Adaptive Security Appliances or to implement any applicable workarounds that are listed in the ‘Workarounds’ section of this advisory. Fixed software is available for the Cisco ASA 5500 Series Adaptive Security Appliances. For more information, refer to the End of Life announcement at:

http://www.cisco.com/en/US/prod/collateral/vpndevc/ps5708/ps5709/ps2030/end_of_life_notice_cisco_pix_525_sec_app.html.

Patch Availability:

Note: Cisco ASA Software versions 7.1.x are affected by some of the vulnerabilities in this advisory. However, no fixed 7.1.x software versions are planned because the 7.1.x major release has reached the End of Software Maintenance Releases milestone. Refer to the EOL/EOS for the Cisco ASA 5500 Series Adaptive Security Appliance Software v7.1 notice for further information.

Fixed Cisco ASA Software can be downloaded from:
http://www.cisco.com/pcgi-bin/tablebuild.pl/ASAPSIRT?psrtdcat20e2

Recommended Releases
+——————-

Releases 7.0(8.10), 7.2(4.46), 8.0(5.9), 8.1(2.40) (available early March 2010), and 8.2(2.4) are recommended releases because they contain the fixes for all vulnerabilities in this advisory. Cisco recommends upgrading to a release that is equal to or later than these recommended releases.

Workaround:

TCP Connection Exhaustion Denial of Service Vulnerability
+——————————————————–

It is possible to mitigate this vulnerability for TCP-based services that are offered to known clients. For example, it may be possible to restrict SSH, Cisco ASDM/HTTPS, and Telnet administrative access to known hosts or IP subnetworks. For other services like remote access SSL VPN, where clients connect from unknown hosts and networks, no mitigations exist.

SIP Inspection Denial of Service Vulnerabilities
+———————————————–

These vulnerabilities can be mitigated by disabling SIP inspection if it is not required. Administrators can disable SIP inspection by issuing the ‘no inspect sip’ command in class configuration sub-mode within policy-map configuration.

SCCP Inspection Denial of Service Vulnerability
+———————————————-

This vulnerability can be mitigated by disabling SCCP inspection if it is not required. Administrators can disable SCCP inspection by issuing the ‘no inspect skinny’ command in class configuration sub-mode within the policy-map configuration.

WebVPN DTLS Denial of Service Vulnerability
+——————————————

This vulnerability can be mitigated by disabling DTLS transport for WebVPN. Administrators can disable DTLS by issuing the ‘no svc dtls enable’ command under the ‘webvpn’ attributes section of the corresponding group policy.

Crafted TCP Segment Denial of Service Vulnerability
+————————————————–

Possible workarounds for this vulnerability are the following:

* Migrate from ‘nailed’ static NAT entries to TCP-state bypass.
* Use the Cisco AIP-SSM in promiscuous mode. This mode can be configured by issuing the ‘ips promiscuous’ command in ‘class’ configuration mode.
* Disable IPS inspection for ‘nailed’ static NAT entries.
* If possible, change ‘nailed’ static NAT entries to standard static NAT entries.

Crafted IKE Message Denial of Service Vulnerability
+————————————————–

A workaround for this vulnerability is to prevent UDP port 4500 traffic from ever traversing IPsec tunnels terminating on the Cisco ASA 5500 Series Adaptive Security Appliance. This may be feasible since in most cases there is no need for allowing IPsec tunnels inside IPsec tunnels. Filtering out UDP port 4500 traffic across an IPsec tunnel can be accomplished by using a VPN filter, as shown in the following example:

!– Deny only UDP port 4500 traffic and allow everything else

access-list VPNFILTER extended deny udp any any eq 4500
access-list VPNFILTER extended permit ip any any

!– Create a group policy and specify a VPN filter that uses the
!– previous ACL

group-policy VPNPOL internal
group-policy VPNPOL attributes
vpn-filter value VPNFILTER

!– Reference the group policy with the VPN filter from the tunnel group

tunnel-group 172.16.0.1 type ipsec-l2l
tunnel-group 172.16.0.1 general-attributes
default-group-policy VPNPOL

For this workaround to be effective, the group policy needs to be applied to all site-to-site (tunnel type ‘ipsec-l2l’) and remote access (tunnel type ‘ipsec-ra’) tunnel groups.

Warning: In addition to filtering out IKE traffic on UDP port 4500, this workaround may also affect other procotols like DNS and SNMP that send traffic on UDP port 4500. For example, if a DNS resolver sends traffic from UDP port 4500 to a DNS server, the response from the DNS server will be destined to UDP port 4500, which then may be filtered out by the filter used in this workaround.

For a more comprehensive example of the VPN filter feature of the Cisco ASA 5500 Series Adaptive Security Appliances, refer to the whitepaper ‘PIX/ASA 7.x and Later: VPN Filter (Permit Specific Port or Protocol) Configuration Example for L2L and Remote Access’ available at:

http://www.cisco.com/en/US/products/hw/vpndevc/ps2030/products_configuration_example09186a00808c9a87.shtml

In addition, if the security appliance does not terminate any tunnels, the vulnerability can be mitigated by disabling IKE by issuing the ‘no isakmp enable <interface name>’ command.

NTLMv1 Authentication Bypass Vulnerability
+—————————————–

If NTLMv1 authentication is required, there are no workarounds for this vulnerability. If NTLMv1 authentication can be substituted by other authentication protocols (LDAP, RADIUS, TACACS+, etc.), it is possible to mitigate the vulnerability.

CVE Information:
CVE-2010-0568

Disclosure Timeline:
Release Date: 2010-02-17′

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