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GELÖST

Cisco Security Advisory - LDAP and VPN Vulnerabilities in PIX and ASA Appliances

Frage Sicherheit

Mitglied: gnarff

gnarff (Level 2) - Jetzt verbinden

02.05.2007 um 19:58 Uhr, 7764 Aufrufe

Da ich weiss, dass hier nicht wenige PIX und ASA Apps laufen haben, werde ich das mal hier posten. Es ist gerade eben, am 02.05.2007, 19:00 herausgegeben worden.
Ich habe leider keine Zeit das noch zusammenzufassen und zu uebersetzen.
Sorry folks!
saludos
gnarff

Cisco Security Advisory: LDAP and VPN Vulnerabilities in PIX and ASA
Appliances

Advisory ID: cisco-sa-20070502-asa

http://www.cisco.com/warp/public/707/cisco-sa-20070502-asa.shtml

Revision 1.0

Last Updated 2007 May 02 1600 UTC (GMT)

For Public Release 2007 May 02 1600 UTC (GMT)

- - ---------------------------------------------------------------------

Contents

Summary
Affected Products
Details
Vulnerability Scoring Details
Impact
Software Version Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of this Notice: FINAL
Distribution
Revision History
Cisco Security Procedures

- - ---------------------------------------------------------------------

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

http://www.cisco.com/warp/public/707/cisco-sa-20070502-asa.shtml

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.

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

                              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 results in a reload of the device.

                              This vulnerability is documented as software bug CSCsh81111.

                              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 results in a reload of the device.

                              More details are available in bug CSCsi16248.

                              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
                              http://intellishield.cisco.com/security/alertmanager/cvss

                              Cisco Bug IDs:

                              CSCsh42793 - LDAP Authentication Bypass for L2TP Sessions

                              CVSS Base Score: 8.0
                              Access Vector: Remote
                              Access Complexity: High
                              Authentication: Not Required
                              Confidentiality Impact: Complete
                              Integrity Impact: Complete
                              Availability Impact: Complete
                              Impact Bias: Normal

                              CVSS Temporal Score: 6.6
                              Exploitability: Functional
                              Remediation Level: Official-Fix
                              Report Confidence: Confirmed


                              CSCsh42793 - LDAP Authentication Bypass for L2TP Sessions

                              CVSS Base Score: 3.3
                              Access Vector: Remote
                              Access Complexity: Low
                              Authentication: Not Required
                              Confidentiality Impact: None
                              Integrity Impact: None
                              Availability Impact: Complete
                              Impact Bias: Normal

                              CVSS Temporal Score: 2.7
                              Exploitability: Functional
                              Remediation Level: Official-Fix
                              Report Confidence: Confirmed


                              CSCsi16248 - Denial of Service in SSL VPNs

                              CVSS Base Score: 3.3
                              Access Vector: Remote
                              Access Complexity: Low
                              Authentication: Not Required
                              Confidentiality Impact: None
                              Integrity Impact: None
                              Availability Impact: Complete
                              Impact Bias: Normal

                              CVSS Temporal Score: 2.7
                              Exploitability: Functional
                              Remediation Level: Official-Fix
                              Report Confidence: Confirmed


                              Impact

                              Successful exploitation of the LDAP Authentication bypass
                              vulnerability may allow unauthorized users to access the device or
                              internal resources. The DoS vulnerability in VPN password expiry and
                              the DoS vulnerability in clientless SSL VPNs could be repeatedly
                              exploited to cause an extended DoS condition.

                              Software Version Fixes

                              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.

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

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

                              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
                              Intelligence companion document for this advisory at the following
                              link:
                              http://www.cisco.com/warp/public/707/cisco-air-20070502-asa.shtml

                              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# config t
                                  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_configurati ...

                                  Information on configuring L2TP over IPSEC using the ADSM can be found
                                  at:

                                  http://www.cisco.com/en/US/partner/products/ps6121/products_configurati ...

                                      • 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/c ....

                                      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# config t
                                      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# config t
                                      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_c ...

                                      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_examp ...

                                      Obtaining Fixed Software

                                      Cisco will make free software available to address this vulnerability
                                      for affected customers. This advisory will be updated as fixed
                                      software becomes available. Prior to deploying software, customers
                                      should consult their maintenance provider or check the software for
                                      feature set compatibility and known issues specific to their
                                      environment.

                                      Customers may only install and expect support for the feature sets
                                      they have purchased. By installing, downloading, accessing or
                                      otherwise using such software upgrades, customers agree to be bound by
                                      the terms of Cisco's software license terms found at
                                      http://www.cisco.com/public/sw-license-agreement.html, or as otherwise
                                      set forth at Cisco.com Downloads at
                                      http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

                                      Registered users can download the latest ASA and PIX releases at:
                                      http://www.cisco.com/cgi-bin/tablebuild.pl/asa-interim
                                      http://www.cisco.com/cgi-bin/tablebuild.pl/pix-interim

                                      Do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
                                      for software upgrades.

                                      Customers with Service Contracts
                                      +-------------------------------

                                      Customers with contracts should obtain upgraded software through
                                      their regular update channels. For most customers, this means that
                                      upgrades should be obtained through the Software Center on Cisco's
                                      worldwide website at http://www.cisco.com.

                                      Customers using Third Party Support Organizations
                                      +------------------------------------------------

                                      Customers whose Cisco products are provided or maintained through
                                      prior or existing agreement with third-party support organizations
                                      such as Cisco Partners, authorized resellers, or service providers
                                      should contact that support organization for guidance and assistance
                                      with the appropriate course of action in regards to this advisory.

                                      The effectiveness of any workaround or fix is dependent on specific
                                      customer situations such as product mix, network topology, traffic
                                      behavior, and organizational mission. Due to the variety of affected
                                      products and releases, customers should consult with their service
                                      provider or support organization to ensure any applied workaround or
                                      fix is the most appropriate for use in the intended network before it
                                      is deployed.

                                      Customers without Service Contracts
                                      +----------------------------------

                                      Customers who purchase direct from Cisco but who do not hold a Cisco
                                      service contract and customers who purchase through third-party
                                      vendors but are unsuccessful at obtaining fixed software through
                                      their point of sale should get their upgrades by contacting the Cisco
                                      Technical Assistance Center (TAC). TAC contacts are as follows.

                                          • +1 800 553 2447 (toll free from within North America)
                                          • +1 408 526 7209 (toll call from anywhere in the world)
                                          • e-mail: tac@cisco.com

                                      Have your product serial number available and give the URL of this
                                      notice as evidence of your entitlement to a free upgrade. Free
                                      upgrades for non-contract customers must be requested through the
                                      TAC.

                                      Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml
                                      for additional TAC contact information, including special localized
                                      telephone numbers and instructions and e-mail addresses for use in
                                      various languages.
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