Summary

• Multiple vulnerabilities exist in the Cisco Adaptive Security Appliance (ASA) and PIX security appliances. These vulnerabilities include two Lightweight Directory Access Protocol (LDAP) authentication bypass vulnerabilities and two denial of service (DoS) vulnerabilities.

  The Lightweight Directory Access Protocol (LDAP) authentication bypass vulnerabilities are caused by a specific processing path followed when the device is setup to use a Lightweight Directory Access Protocol (LDAP) authentication server. These vulnerabilities may allow unauthenticated users to access either the internal network or the device itself.

  The two DoS vulnerabilities may be triggered when devices are terminating Virtual Private Networks (VPN). These denial of service vulnerabilities may allow an attacker to disconnect VPN users, prevent new connections, or prevent the device from transmitting traffic.

  These vulnerabilities are distributed in the authentication, IPSec VPN, and SSL VPN code. They are categorized in this advisory by their Cisco bug descriptions:

  • LDAP Authentication Bypass
    
  • Denial of Service in VPNs with Password Expiry
    
  • Denial of Service in SSL VPNs
    

  Cisco has made free software available to address these vulnerabilities for affected customers.

  This advisory is posted at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070502-asa.

Affected Products

• Vulnerable Products

  Cisco ASA and PIX security appliances that are running software versions 7.1 and 7.2 may be vulnerable. To identify the vulnerable versions for a specific issue, please consult the table below.

  Vulnerability	Affected Software Version
  LDAP Authentication bypass	7.2 versions prior to 7.2(2)8
  Denial of Service in VPNs with password expiry	7.1 versions prior to 7.1(2)49 7.2 versions prior to 7.2(2)17
  Denial of Service in SSL VPNs	7.1 versions prior to 7.1(2)49 7.2 versions prior to 7.2(2)19

  To determine the version of Cisco ASA or PIX system software your device is running, log into command line interface (CLI) of the device and issue the show version command. This example shows an ASA that runs software release 7.2(2)10:

  ciscoasa#show version
  
  Cisco Adaptive Security Appliance Software Version 7.2(2)10

  For customers that manage their devices through the Cisco Adaptive Security Device Manager (ASDM), log into the application, and the version can be found either in the table in the login window or in the upper left hand corner of the ASDM window indicated by a label similar to:

  PIX Version 7.2(2)10

  Cisco ASA and PIX security appliances running affected software version are only vulnerable if they are running one of the following configurations:

  LDAP Authentication Bypass Vulnerability

  Two configuration scenarios exist where Cisco PIX or ASA devices are vulnerable:

  • Layer 2 Tunneling Protocol (L2TP)
    Devices configured to use a LDAP authentication server and use an authentication protocol other than PAP may be vulnerable. The LDAP server is specified in the configuration via the aaa-server ldap server host <ip address> command line interface (CLI) configuration command. The authentication protocol is specified via the authentication <protocol> command within the tunnel-group <tunnel-group> ppp-attributes section of the configuration.
    Relevant configuration segments of a vulnerable device are shown below. In the following example configuration, the authentication server is specified as LDAP and the authentication protocol is specified as ms-chap-v2:
    

    aaa-server ldap_server protocol ldap
    aaa-server ldap_server host 192.168.1.100
     timeout 5
     ldap-scope onelevel
    
    tunnel-group example_l2tp_group general-attributes
     address-pool inside_addresses
     authentication-server-group ldap_server
    
    tunnel-group example_l2tp_group ppp-attributes
     authentication ms-chap-v2
    

  • Remote Management Access
    Devices configured to allow remote management access (telnet, SSH, HTTP) and use LDAP authentication, authorization, accounting (AAA) server for credential validation may be vulnerable.
    In the configuration file, the server_group is defined as a LDAP server with the command aaa-server <server_group> protocol ldap. The LDAP authentication server for remote management access is defined via the command, aaa authentication {telnet | ssh | http | serial} console server_group.
    Relevant configuration segments of a vulnerable device are shown below. The authentication server is specified as LDAP, and remote management access for SSH is permitted and credentials checked by the defined LDAP AAA server:
    

    ssh 192.168.1.2 255.255.255.255 inside
    
    aaa-server ldap_server protocol ldap
    aaa-server ldap_server host 192.168.1.100
     timeout 5
     ldap-scope onelevel
    aaa authentication ssh console ldap_server
    

  Denial of Service in VPNs with Password Expiry

  A device may be affected by this vulnerability if the password-management command is present in the tunnel-group section, as shown in the following examples:

  tunnel-group example_group general-attributes
   address-pool inside_addresses
   default-group-policy example_group
   password-management

  tunnel-group example_group general-attributes
   address-pool inside_addresses
   default-group-policy example_group
   password-management password-expire-in-days 30

  Denial of Service in SSL VPNs

  Clientless SSL VPNs must be enabled on an interface in order for the device to be affected by this vulnerability.

  Devices with clientless SSL VPNs enabled have a webvpn section in the running configuration. This will be similar to the following entry:

  webvpn
   enable outside
   url-list ServerList "WSHAWLAP" cifs://10.2.2.2 1
   url-list ServerList "FOCUS_SRV_1" https://10.2.2.3 2
   url-list ServerList "FOCUS_SRV_2" http://10.2.2.4 3
  

  Products Confirmed Not Vulnerable

  The Firewall Services Module (FWSM) is not affected by any of the vulnerabilities disclosed in this advisory.

  Cisco ASA and PIX security appliances are not affected by these vulnerabilities under the following conditions:

  LDAP Authentication Bypass for L2TP Sessions

  ASA and PIX security appliances with the following configurations are not affected by this vulnerability:

  • Devices configured for L2TP over IPSec and using an authentication server other than LDAP
    
  • Devices configured for L2TP over IPSec and using a LDAP authentication server with PAP
    
  • Devices using AAA server other than LDAP or a local database for authentication of remote management sessions
    

  Denial of Service in VPNs with Password Expiry

  Device without remote access tunnel groups configured with password expiry are not susceptible to this vulnerability.

  Denial of Service in SSL VPNs

  Devices not configured to support clientless SSL VPN connections are not susceptible to this vulnerability. PIX Security Appliances do not support clientless SSL VPN connections and are not vulnerable.

Details

• The PIX is a firewall appliance that delivers user and application policy enforcement, multi-vector attack protection, and secure connectivity services.

  The Adaptive Security Appliance (ASA) is a modular platform that provides security and VPN services. The ASA offers firewall, intrusion prevention (IPS), anti-X, and VPN services.

  LDAP Authentication Bypass

  Cisco ASA and PIX devices leveraging LDAP AAA servers for authentication of terminating L2TP IPSec tunnels or remote management sessions may be vulnerable to an authentication bypass attack. See the following bullets for more details:

  • Layer 2 Tunneling Protocol (L2TP)
    Devices terminating L2TP IPSec tunnels must be configured to use LDAP in conjunction with CHAP, MS-CHAPv1, or MS-CHAPv2 authentication protocols to be vulnerable. If LDAP authentication is used in conjunction with PAP, the device is not vulnerable to the LDAP L2TP authentication bypass.
    
  • Remote Management Access
    Cisco ASA and PIX devices leveraging LDAP AAA servers for authentication of management sessions (telnet, SSH and HTTP) may be vulnerable to an authentication bypass attack. Access for management sessions must be explicitly enabled and is limited to the defined source IP address within the device configuration.
    

  This vulnerability is documented as bug ID CSCsh42793 ( registered customers only) .

  Denial of Service in VPNs with Password Expiry

  Cisco ASA and PIX devices terminating remote access VPN connections may be vulnerable to a DoS attack if the tunnel group is configured with password expiry. To exploit this vulnerability for IPSec VPN connections, an attacker would need to know the group name and group password. An attacker would not need this information for SSL VPN connections. A successful attack may result in a reload of the device.

  This vulnerability is documented as software bug CSCsh81111 ( registered customers only) .

  Denial of Service in SSL VPNs

  Cisco ASAs using clientless SSL VPNs are vulnerable to a denial of service attack via the SSL VPN HTTP server. A successful attack must exploit a race condition in the processing non-standard SSL sessions and may result in a reload of the device.

  More details are available in bug CSCsi16248 ( registered customers only) .

  Vulnerability Scoring Details

  Cisco is providing scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS).

  Cisco will provide a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

  Cisco PSIRT will set the bias in all cases to normal. Customers are encouraged to apply the bias parameter when determining the environmental impact of a particular vulnerability.

  CVSS is a standards based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

  Cisco has provided an FAQ to answer additional questions regarding CVSS at http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

  Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at https://sec.cloudapps.cisco.com/security/center/cvssCalculator.x .

  LDAP Authentication Bypass for L2TP Sessions Calculate the environmental score of CSCsh42793
  CVSS Base Score - 8
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact	Impact Bias
  Remote	High	Not Required	Complete	Complete	Complete	Normal
  CVSS Temporal Score - 6.6
  Exploitability		Remediation Level		Report Confidence
  Functional		Official-Fix		Confirmed

  Denial of Service in VPNs with Password Expiry Calculate the environmental score of CSCsh81111
  CVSS Base Score - 3.3
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact	Impact Bias
  Remote	Low	Not Required	None	None	Complete	Normal
  CVSS Temporal Score - 2.7
  Exploitability		Remediation Level		Report Confidence
  Functional		Official-Fix		Confirmed

  Denial of Service in SSL VPNs Calculate the environmental score of CSCsi16248
  CVSS Base Score - 3.3
  Access Vector	Access Complexity	Authentication	Confidentiality Impact	Integrity Impact	Availability Impact	Impact Bias
  Remote	Low	Not Required	None	None	Complete	Normal
  CVSS Temporal Score - 2.7
  Exploitability		Remediation Level		Report Confidence
  Functional		Official-Fix		Confirmed

Workarounds

• This section of the advisory describes workarounds that may be useful in some environments. Additional mitigations that can be deployed on Cisco devices within the network are available in the Cisco Applied Mitigation Bulletin companion document for this advisory at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20070502-asa

  LDAP Authentication bypass

  The following workarounds may be a useful reference for some customers to mitigate the LDAP authentication bypass vulnerabilities.

  • L2TP
    For Cisco ASA or PIX devices configured to use a LDAP authentication server for L2TP over IPSec connections, configuring the device to use PAP as an authentication protocol may mitigate this vulnerability. It is important to note that PAP transmits passwords in clear-text. PAP authentication is encrypted via IPSec when it is used for the L2TP connection. Communications between the security appliance and the LDAP server are not encrypted by default and can be secured with SSL using the ldap-over-ssl command. Configuration of PAP authentication can be done using the following example as a guide or by referring to the security appliance configuration guides listed:
    

    ciscoasa#configure terminal
    ciscoasa(config)#tunnel-group l2tp_group ppp-attributes
    ciscoasa(config-ppp)#authentication pap
    ciscoasa(config-ppp)#no authentication ms-chap-v1
    ciscoasa(config-ppp)#no authentication ms-chap-v2
    ciscoasa(config-ppp)#no authentication chap
    

    Information on configuring L2TP over IPSEC using the CLI is available at the following link: http://www.cisco.com/en/US/partner/products/ps6120/products_configuration_guide_chapter09186a008066ebb6.html
    Information on configuring L2TP over IPSEC using the ADSM can be found at: http://www.cisco.com/en/US/partner/products/ps6121/products_configuration_guide_chapter09186a00806a81bc.html
    
  • Remote Management
    Cisco ASA or PIX devices that authenticate remote management sessions with either the local database or an AAA server other than a LDAP server are not affected by this vulnerability. More information on changing the AAA server protocol used with remote management sessions is available at the following link: http://www.cisco.com/univercd/cc/td/doc/product/multisec/asa_sw/v_7_2/conf_gd/sysadmin/mgaccess.htm.
    Remote management sessions must be explicitly enabled before the Cisco ASA or PIX will accept sessions. The source IP addresses are defined within the command that enables remote management access. Below are examples of enabling remote management sessions (Note that other commands are required, but these commands control the source IP address of the device that is allowed access to the Cisco ASA or PIX device):
    For remote telnet, ssh and http access:
    

    ciscoasa#configure terminal
    ciscoasa(config)#telnet source_IP_address mask source_interface 
    ciscoasa(config)#ssh source_IP_address mask source_interface
    ciscoasa(config)#http source_IP_address mask source_interface
    

  Denial of Service in VPNs with Password Expiry

  Disabling password expiry for remote access users until a device can be updated with non-vulnerable code can prevent the exposure of this vulnerability. This can be accomplished by removing the password management entry in the general attributes of the tunnel group, as shown in the following example:

  ciscoasa#configure terminal
  ciscoasa(config)#tunnel-group remote_access_group general-attributes
  ciscoasa(config-tunnel-general)#no password-management
  

  Implementing this workaround will disable the password expiry feature, and users will not be forced to change their passwords.

  More information on the password-management command is available in the Security Appliance Command reference at the following link: http://www.cisco.com/en/US/products/ps6120/products_command_reference_chapter09186a008063f0f8.html#wp1725278

  Denial of Service in SSL VPNs

  If clientless SSL VPNs are used, there is no workaround for the SSL VPN vulnerability. Client-based VPNs are not affected, and may be used as an alternative to the clientless VPN connections.

  More information on configuring clientless SSL VPNs on the ASA is available in the configuration example at the following link: http://www.cisco.com/en/US/products/ps6120/products_configuration_example09186a00806ea271.shtml

Fixed Software

• When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

  In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.

  Vulnerability	First Fixed Release
  	7.1	7.2
  LDAP Authentication Bypass	Not affected	7.2(2)8
  Denial of Service in VPNs with Password Expiry	7.1(2)49	7.2(2)17
  Denial of Service in SSL VPNs	7.1(2)49	7.2(2)19

  More information on how and where to obtain fixed software can be found in the Obtaining Fixed Software section of this advisory.

Exploitation and Public Announcements

• The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

  These vulnerabilities were reported to Cisco by customers that experienced these issues during normal operation of their equipment.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20070502-asa

Revision History

• Revision 1.1	2008-April-24	Updated links to the CVSS scoring for CSCsh81111 and CSCsi16248.
  Revision 1.0	2007-May-02	Initial public release

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