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

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.