Advisory ID: cisco-sa-20071017-fwsmRevision 1.1
For Public Release 2007 October 17 16:00 UTC (GMT)
Two crafted packet vulnerabilities exist in the Cisco Firewall Services
Module (FWSM) that may result in a reload of the FWSM. These vulnerabilities
can be triggered during the processing of HTTPS requests, or during the
processing of Media Gateway Control Protocol (MGCP) packets.
A third vulnerability may cause access control list (ACL) entries to
not be evaluated after the access list has been manipulated.
Note: These vulnerabilities are independent of each other; a device may be
affected by one and not by the others.
This advisory is posted at
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071017-fwsm.
The FWSM is affected by a crafted HTTPS request vulnerability if the
HTTPS server on the FWSM is enabled and is running software versions 3.1(5) and
prior or 3.2(1). Version 2.3.x is not affected. The HTTPS server is not enabled
by default.
The FWSM is affected by a crafted MGCP packet vulnerability if MGCP
application layer protocol inspection is enabled and the device is running
software version 3.1(5) and prior. Versions 2.3.x and 3.2.x are not affected.
MGCP inspection is not enabled by default.
The FWSM is affected by an access control list corruption vulnerability
that may result in the ACL not working properly, i.e. the ACL may allow traffic
that would normally be denied, or would deny traffic that would normally be
permitted. Affected versions include 3.1(6) and prior and 3.2(2) and prior.
Version 2.3.x is not affected.
In addition to the FWSM, the crafted MGCP packet vulnerability also
affects the PIX 500 Series Security Appliances and the Cisco ASA 5500 Series
Adaptive Security Appliances. More information regarding vulnerabilities
affecting the PIX and ASA can be found in the companion advisory located at
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071017-asa.
To determine if you are running a vulnerable version of FWSM software,
issue the show module command-line interface (CLI)
command from Cisco IOS or Cisco CatOS to identify what modules and sub-modules
are installed in the system.
The following example shows a system with a Firewall Service Module
(WS-SVC-FWM-1) installed in slot 4.
switch#show module
Mod Ports Card Type Model Serial No.
--- ----- -------------------------------------- ----------------- -----------
1 48 SFM-capable 48 port 10/100/1000mb RJ45 WS-X6548-GE-TX SAxxxxxxxxx
4 6 Firewall Module WS-SVC-FWM-1 SAxxxxxxxxx
5 2 Supervisor Engine 720 (Active) WS-SUP720-BASE SAxxxxxxxxx
6 2 Supervisor Engine 720 (Hot) WS-SUP720-BASE SAxxxxxxxxx
After locating the correct slot, issue the show module
<slot number> command to identify the software version that
is running:
switch#show module 4
Mod Ports Card Type Model Serial No.
--- ----- -------------------------------------- ----------------- -----------
4 6 Firewall Module WS-SVC-FWM-1 SAxxxxxxxxx
Mod MAC addresses Hw Fw Sw Status
--- --------------------------------- ------ ------------ ------------ -------
4 0003.e4xx.xxxx to 0003.e4xx.xxxx 3.0 7.2(1) 3.1(3) Ok
The example above shows that the FWSM is running version 3.1(3) as
indicated by the column under "Sw" above.
Note: Recent versions of Cisco IOS will show the software version of
each module in the output from the show module
command; therefore, executing the show module <slot
number> command is not necessary.
Alternatively, the information may also be obtained directly from the
FWSM through the show version command as seen below.
FWSM#show version
FWSM Firewall Version 3.1(3)
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. The
version notation is similar to this:
FWSM Version: 3.1(3)
No other Cisco products are currently known to be affected by these vulnerabilities. This Security Advisory describes multiple distinct vulnerabilities.
These vulnerabilities are independent of each other.
A FWSM that has the HTTPS server enabled may reload if a crafted HTTP
request is processed by the device. The HTTPS server is disabled by
default.
The source IP address and interface on which the HTTPS request is
received must comply with the configured http <source IP>
<address mask> <source interface> command. For
example, if the command http 10.10.10.0 255.255.255.0
inside is present in the configuration, then only crafted HTTPS
requests coming from the 10.10.10.0/24 network may represent an issue for the
device.
No other HTTP(s) services are known to be affected, such as HTTP
Inspection, HTTP/HTTPS Proxy Server, and HTTP redirect.
To confirm if the HTTPS server is enabled, log in to the FWSM and issue
the CLI command show running-config | include http.
If the output contains both http server enable and
http <source IP> <address mask> <source
interface>, then the device has a vulnerable configuration.
The following example shows an FWSM with a vulnerable configuration:
FWSM# show running-config | include http
http server enable
http 10.10.10.0 255.255.255.0 inside
FWSM#
This vulnerability is documented in Cisco Bug ID
CSCsi77844
(
registered customers only)
and does not affect the PIX or ASA
security appliances.
An FWSM that has the MGCP application layer protocol inspection feature
enabled may reload when a crafted MGCP packet is processed by the device. MGCP
application layer protocol inspection is not enabled by default.
MGCP messages are transmitted over the User Datagram Protocol (UDP),
which does allow the crafted MGCP messages to be sourced from a spoofed
address. Only the MGCP for gateway application (MGCP traffic on UDP port 2427)
is affected.
To determine whether MGCP inspection is configured on the FWSM, log in
to the device and issue the CLI command show service-policy |
include mgcp. If the output contains the text
Inspect: mgcp and some statistics, then the device
has a vulnerable configuration. The following example shows a vulnerable
FWSM:
FWSM# show service-policy | include mgcp
Inspect: mgcp, packet 66, drop 0, reset-drop 0
FWSM#
This vulnerability is documented in Cisco Bug ID
CSCsi00694
(
registered customers only)
. The corresponding Cisco Bug ID for the
PIX and ASA security appliances, included in the companion PIX/ASA Security
Advisory, is
CSCsi90468
(
registered customers only)
.
This vulnerability may cause access control list entries (ACEs) in an
ACL that has been manipulated to not be evaluated. Manipulation of the ACL can
take place via the command-line interface or ASDM and consists of deleting and
re-adding ACEs. When the access list is manipulated in this way, the internal
structure that represents the ACL becomes corrupted, resulting in the FWSM not
evaluating some ACEs.
Because ACEs in an ACL may not be evaluated, the ACL may allow traffic
that would normally be denied, or deny traffic that would normally be
permitted.
This vulnerability is documented in Cisco Bug ID
CSCsj52536
(
registered customers only)
and does not affect the PIX or ASA
security appliances.
Successful exploitation of the crafted packet vulnerabilities that are
described in this advisory will result in a reload of the affected device.
Repeated exploitation can result in a sustained denial of service (DoS)
attack.
In the case of the "Manipulation of ACL May Cause ACL Corruption"
vulnerability, a device that becomes affected after an administrator
manipulates an ACL may allow traffic that would normally be denied, or deny
traffic that would normally be permitted. If the ACL is used for other
functions like NAT (policy NAT and NAT exemption), AAA (auth-proxy), control of
access to the device (SSH, Telnet, HTTP, ICMP), then those functions may be
adversely affected as well.
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 that 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.
The following list contains the first fixed software release
for each vulnerability:
|
Vulnerability
|
Affected Major Release
|
First Fixed Release
|
|
Crafted HTTPS Request
|
2.3
|
Not affected
|
|
3.1
|
3.1(6)
|
|
3.2
|
3.2(2)
|
|
Crafted MGCP packet
|
2.3
|
Not affected
|
|
3.1
|
3.1(6)
|
|
3.2
|
Not affected
|
|
Manipulation of ACL May Cause ACL Corruption
|
2.3
|
Not affected
|
|
3.1
|
3.1(7)
|
|
3.2
|
3.2(3) - tentatively available Q4CY07
|
FWSM software versions 3.1(7) and 3.2(3) contain the fixes for all the
vulnerabilities described in this document.
FWSM software is available for download from the following location on
cisco.com:
http://www.cisco.com/pcgi-bin/tablebuild.pl/cat6000-fwsm?psrtdcat20e2
(
registered customers only)
Filters that deny HTTPS packets using TCP port 443 and MGCP packets on
UDP port 2427 should 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 HTTPS
packets using TCP port 443 and MGCP packets on UDP port 2427 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.
Additional mitigations 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://tools.cisco.com/security/center/content/CiscoAppliedMitigationBulletin/cisco-amb-20071017-asafwsm.
There are no workarounds for these vulnerabilities other than disabling
the HTTPS server on the device. See the Cisco Applied Mitigation Bulletin companion
document for mitigations.
Limiting the networks and hosts that can connect to the HTTPS server on
the FWSM can help mitigate this vulnerability. For example, if the command
http 10.10.10.0 255.255.255.0 inside is present in
the configuration, then only hosts on this trusted network can establish HTTPS
sessions with the FWSM. This scenario eliminates the possibility of malicious
hosts on other IP networks launching successful attacks against the
FWSM.
There is no workaround for this vulnerability other than disabling MGCP
application layer protocol inspection on the device.
Leveraging anti-spoofing techniques will help mitigate spoofed packets
from triggering this vulnerability.
Limiting MGCP application layer inspection to traffic between MGCP
gateways may help to mitigate this vulnerability since it would require an
attacker to have additional information (the addresses of the MGCP gateways) to
launch a successful attack. To limit MGCP application layer inspection to
traffic between certain devices, a class map that matches only traffic between
the gateways must be created. Then, MGCP inspection must be performed on
traffic in that class. The following example shows how to accomplish
this:
FWSM(config)# access-list mgcp_traffic permit udp host 192.168.0.1
host 172.16.0.1 eq 2427
FWSM(config)# access-list mgcp_traffic permit udp host 172.16.0.1
host 192.168.0.1 eq 2427
FWSM(config)# class-map MGCP
FWSM(config-cmap)# match access-list mgcp_traffic
FWSM(config-cmap)# exit
FWSM(config)# policy-map global_policy
FWSM(config-pmap)# class inspection_default
FWSM(config-pmap-c)# no inspect mgcp
FWSM(config-pmap-c)# exit
FWSM(config-pmap)# class MGCP
FWSM(config-pmap-c)# inspect mgcp
FWSM(config-pmap-c)# exit
FWSM(config-pmap)# exit
FWSM(config)#
Note that MGCP inspection is applied only to UDP traffic between hosts
192.168.0.1 and 172.16.0.1
See the Cisco Applied Mitigation Bulletin companion document for additional
mitigation possibilities.
A possible workaround for this vulnerability is to completely remove
the ACL before modifying it, and then recreate it with the desired changes.
ACLs can be removed with the command clear configure access-list
<ACL name>.
Note: The ACL corruption does not occur during normal operation of the
device, and it cannot be triggered by some type of traffic. It can only occur
if an administrator makes configuration changes, and more specifically, if an
administrator manipulates an ACL. For this reason, if ACL changes are made only
during a maintenance window and the FWSM is reloaded after making those
changes, there should not be any concerns with this vulnerability.
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.
Do not contact either "psirt@cisco.com" or
"security-alert@cisco.com" for software upgrades.
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 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 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.
The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerabilities described in this advisory.
The crafted packet vulnerabilities were discovered by Cisco
during internal testing of the associated products.
The ACL corruption vulnerability was discovered during the resolution
of customer support cases.
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.
This advisory is posted on Cisco's worldwide website at :
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20071017-fwsm
In addition to worldwide web posting, a text version of this
notice is clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.
-
cust-security-announce@cisco.com
-
first-teams@first.org
-
bugtraq@securityfocus.com
-
vulnwatch@vulnwatch.org
-
cisco@spot.colorado.edu
-
cisco-nsp@puck.nether.net
-
full-disclosure@lists.grok.org.uk
-
comp.dcom.sys.cisco@newsgate.cisco.com
Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on mailing lists or
newsgroups. Users concerned about this problem are encouraged to check the
above URL for any updates.
|
Revision 1.1
|
2007-October-31
|
Updated expected availability date for FWSM version
3.2(3)
|
|
Revision 1.0 |
2007-October-17
|
Initial public release. |
|
