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Credit:
The information has been provided by Cisco Systems Product Security Incident Response Team.
The original article can be found at: http://www.cisco.com/warp/public/707/cisco-sa-20080604-asa.shtml#@ID
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Vulnerable Products:
The following are the details about each vulnerability described within this advisory.
Crafted TCP ACK Packet Vulnerability
Cisco ASA and Cisco PIX devices are affected by a crafted TCP acknowledgment (ACK) packet vulnerability. Software versions prior to 7.1(2)70 on the 7.1.x release, 7.2(4) on the 7.2.x release, and 8.0(3)10 on the 8.0.x release are affected. Cisco ASA or Cisco PIX security appliances running software version 7.0.x, or 8.1.x are not vulnerable.
Cisco ASA and Cisco PIX devices running versions 7.1.x and 7.2.x with WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability. Devices running software versions on the 8.0 release that are configured for Telnet, Secure Shell (SSH), WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability.
Note: Devices running IPv4 and IPv6 are affected by this vulnerability.
Crafted TLS Packet Vulnerability
Cisco ASA and Cisco PIX devices are affected by a crafted TLS request vulnerability if the HTTPS server on the Cisco ASA or Cisco PIX device is enabled and is running software versions prior to 8.0(3)9 on the 8.0.x release or prior to version 8.1(1)1 on the 8.1.x release. Cisco ASA and Cisco PIX appliances running software versions 7.x are not vulnerable.
Instant Messenger Inspection Vulnerability
Cisco ASA and Cisco PIX devices are affected by a crafted packet vulnerability if Instant Messaging Inspection is enabled and the device is running software versions prior to 7.2(4) on the 7.2.x release, 8.0(3)10 on the 8.0.x release, or 8.1(1)2 on the 8.1.x release. Devices running software versions in the 7.0.x and 7.1.x releases are not vulnerable. Additionally, devices that do not have Instant Messaging Inspection enabled are not vulnerable.
Note: Instant Messaging Inspection is disabled by default.
Vulnerability Scan Denial of Service
Cisco ASA and Cisco PIX devices are affected by a vulnerability (port) scan denial of service vulnerability if the device is running software versions prior to 7.2(3)2 on the 7.2.x release or 8.0(2)17 on the 8.0.x release. Cisco ASA and Cisco PIX devices running software versions 7.0.x, 7.1.x, or 8.1.x are not vulnerable.
Control-plane Access Control List Vulnerability
Cisco ASA and Cisco PIX devices are affected by a vulnerability if the device is configured to use control-plane ACLs and if it is running software versions prior to 8.0(3)9 on the 8.0.x release. Devices running software versions 7.x or 8.1.x are not vulnerable.
Note: Control-plane ACLs were first introduced in software version 8.0(2). The control-plane ACLs are not enabled by default.
The show version command-line interface (CLI) command can be used to determine if a vulnerable version of the Cisco PIX or Cisco ASA software is running. The following example shows a Cisco ASA Security Appliance that runs software release 8.0(2):
ASA# show version
Cisco Adaptive Security Appliance Software Version 8.0(2)
Device Manager Version 6.0(1)
[...]
Customers who use the Cisco Adaptive Security Device Manager (ASDM) to manage their devices can find the version of the software displayed in the table in the login window or in the upper left corner of the ASDM window.
Products Confirmed Not Vulnerable
The Cisco Firewall Services Module (FWSM) is not affected by any of these vulnerabilities. Cisco PIX security appliances running versions 6.x are not vulnerable. No other Cisco products are currently known to be affected by these vulnerabilities.
Details
This Security Advisory describes multiple distinct vulnerabilities. These vulnerabilities are independent of each other.
1. Crafted TCP ACK Packet Vulnerability
A crafted TCP ACK packet may cause a denial of service condition on the Cisco ASA or Cisco PIX security appliances. Only packets destined to the device (not transiting the device) may trigger the effects of this vulnerability.
Cisco ASA and Cisco PIX devices running versions 7.1.x and 7.2.x with WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability. Devices running software versions on the 8.0 release that are configured for Telnet, Secure Shell (SSH), WebVPN, SSL VPN, or ASDM enabled are affected by this vulnerability.
The telnet command is used identify the IP addresses from which the security appliance accepts Telnet connections.
ASA(config)# telnet 192.168.10.0 255.255.255.0 inside
In the previous example, the Cisco ASA is configured to accept Telnet connections on the inside interface from the 192.168.10.0/24 network.
Note: You cannot use Telnet to the lowest security interface unless you use Telnet inside an IPSec tunnel.
ASDM management sessions are enabled via the http server enable and http commands.
The ssh command is used identify the IP addresses from which the security appliance accepts SSH connections. For example:
ASA(config)# ssh 192.168.10.0 255.255.255.0 inside
In the previous example the Cisco ASA is configured to accept SSH connections on the inside interface from the 192.168.10.0/24 network.
Clientless WebVPN, SSL VPN Client, and AnyConnect connections are enabled via the webvpn command. For example, the following configuration shows a Cisco ASA with WebVPN configured and enabled. In this case the ASA will listen for WebVPN connections on the default port, TCP port 443:
http server enable
!
webvpn
enable outside
Note that with this particular configuration, the device is vulnerable to attacks coming from the outside interface.
This vulnerability is documented in Cisco Bug ID CSCsm84110 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2055.
2. Crafted TLS Packet Vulnerability
Transport Layer Security (TLS) is the replacement for the Secure Socket Layer (SSL) protocol. It is a protocol that provides, via cryptography, secure communications between two end-points.
The Cisco PIX and Cisco ASA security appliances rely on TLS to protect the confidentiality of communications in a variety of scenarios. In all these scenarios, the PIX and ASA may be affected by a vulnerability in the handling of the TLS protocol that may lead to a reload of the device when it processes specially crafted TLS packets.
Note: Only packets destined to the device (not transiting the device) may trigger the effects of this vulnerability.
The following list contains some of the applications within the Cisco ASA and Cisco PIX devices that use TLS:
* Clientless WebVPN, SSL VPN Client, and AnyConnect Connections
* ASDM (HTTPS) Management Sessions
* Cut-Through Proxy for Network Access
* TLS Proxy for Encrypted Voice Inspection
Clientless WebVPN, SSL VPN Client, and AnyConnect Connections
Clientless WebVPN, SSL VPN Client, and AnyConnect connections are enabled via the webvpn command. For example, the following configuration shows a Cisco ASA with WebVPN configured and enabled. In this case the ASA will listen for WebVPN connections on the default port, TCP port 443:
http server enable
!
webvpn
enable outside
Note that with this particular configuration, the device is vulnerable to attacks coming from the outside interface.
ASDM (HTTPS) Management Sessions
ASDM management sessions are enabled via the http server enable and http commands. For example, the following configuration shows an ASA configured for remote HTTPS management:
http server enable
http 192.168.0.0 255.255.255.0 inside
Note that with this particular configuration the device is vulnerable to attacks coming from the inside interface and from the 192.168.0.0/24 IP sub-network.
Cut-Through Proxy for Network Access
The cut-through proxy feature is used to authenticate users before they can access the network. The following is an example of a configuration that requires users to authenticate before they can be granted network access:
access-list auth-proxy extended permit tcp any any eq www
access-list auth-proxy extended permit tcp any any eq telnet
access-list auth-proxy extended permit tcp any any eq https
!
aaa authentication match auth-proxy inside LOCAL
aaa authentication secure-http-client
aaa authentication listener https inside port https
A configuration affected by this vulnerability will contain the command aaa authentication secure-http-client or aaa authentication listener https inside port <port number>. Note that with the configuration in the preceding example, the device is vulnerable to attacks coming from the inside interface.
TLS Proxy for Encrypted Voice Inspection
The TLS proxy for encrypted voice inspection feature allows the security appliance to decrypt, inspect and modify (as needed, for example, performing NAT fixup), and re-encrypt voice signaling traffic while all of the existing VoIP inspection functions for SCCP and Session Initiation Protocol (SIP) protocols are preserved. Once voice signaling is decrypted, the plain-text signaling message is passed to the existing inspection engines. The security appliance accomplishes this by acting as a TLS proxy between the IP phone and Cisco Unified CallManager and Cisco Unified Communications Manager, which implies that TLS sessions are terminating on the security appliance. This is done over TCP ports 2443 and 5061.
To determine whether the Cisco PIX or Cisco ASA security appliance is configured to support inspection of encrypted voice, log in to the device and issue the CLI command show service-policy | include tls. If the output contains the text tls-proxy: active and some statistics, then the device has a vulnerable configuration. The following example shows a vulnerable Cisco ASA Security Appliance:
ASA# show service-policy | include tls
Inspect: sip tls-proxy myproxy, packet 0, drop 0, reset-drop 0
tls-proxy: active sess 0, most sess 0, byte 0
Inspect: skinny tls-proxy myproxy, packet 0, drop 0, reset-drop 0
tls-proxy: active sess 0, most sess 0, byte 0
ASA#
This vulnerability is documented in Cisco Bug ID CSCsm26841 ( registered customers only) and has been assigned the Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2056.
3. Instant Messenger Inspection Vulnerability
The Cisco ASA and Cisco PIX Instant Messenger (IM) inspection engine is used to apply fine grained controls on the IM application usage within your network. The Cisco ASA and Cisco PIX is affected by a denial of service vulnerability if the Instant Messaging Inspection is enabled.
More information on the IM inspection feature and its configuration can be found at:
http://www.cisco.com/en/US/docs/security/asa/asa80/configuration/guide/inspect.html#wp1479354
This vulnerability is documented in Cisco Bug ID CSCso22981 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2057.
4. Vulnerability Scan Denial of Service
The Cisco ASA and Cisco PIX security appliances are affected by a denial of service vulnerability when a vulnerability scan is conducted against TCP port 443. Certain vulnerability (port) scanners will cause the system to reload.
Note: This vulnerability is affected by traffic destined to the device on TCP port 443. The Cisco ASA and Cisco PIX security appliances use TCP port 443 for Clientless WebVPN, SSL VPN Client, AnyConnect client connections, HTTPS Management Sessions, Cut-Through Proxy for Network Access, and TLS Proxy for Encrypted Voice Inspection. Please refer to the details of the Crafted TLS Packet Vulnerability for additional information on these services.
This vulnerability is documented in Cisco Bug ID CSCsj60659 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2058.
5. Control-plane Access Control List Vulnerability
Control-plane ACLs are designed to protect traffic destined to the security appliance. A vulnerability exist in the Cisco ASA and Cisco PIX security appliances where a control-plane ACL may not work after it is initially configured on the device.
The following example uses the show running-config | include control-plane command to determine if a control-plane ACL is configured on the device:
ASA# show running-config | include control-plane
access-group 101 in interface inside control-plane
ASA#
This vulnerability is documented in Cisco Bug ID CSCsm67466 ( registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) identifier CVE-2008-2059.
Impact
Successful exploitation of the first four vulnerabilities may cause a reload of the affected device. Repeated exploitation could result in a sustained Denial-of-Service (DoS) condition. Successful exploitation of the fifth vulnerability may allow an attacker to bypass control-plane ACLs and successfully send malicious traffic to the device.
Workarounds
This Security Advisory describes multiple distinct vulnerabilities. These vulnerabilities and their respective workarounds are independent of each other.
Crafted TCP ACK Packet Vulnerability
As a workaround and best practice allow Telnet, SSH, and ASDM connections from only trusted hosts in your network.
Additionally, filters that deny TCP ports 22, 23, 80, and 443 packets may be deployed throughout the network as part of a transit ACL (tACL) policy for protection of traffic which enters the network at ingress access points. This policy should be configured to protect the network device where the filter is applied and other devices behind it. Filters for packets using TCP ports 22, 23, 80, and 443 should also be deployed in front of vulnerable network devices so that traffic is only allowed from trusted clients.
Additional information about tACLs is available in "Transit Access Control Lists : Filtering at Your Edge":
http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a00801afc76.shtml
Crafted TLS Packet Vulnerability
There are no workarounds for this vulnerability.
Instant Messenger Inspection Vulnerability
The only workaround for this vulnerability is to disable IM inspection on the security appliance.
Port Scan Denial of Service Vulnerability
There are no workarounds for this vulnerability.
Control-plane Access Control List Vulnerability
There are no workarounds for this vulnerability.
Additional mitigation techniques that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory:
http://www.cisco.com/warp/public/707/cisco-amb-20080604-asa.shtml
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