Cisco Security Advisory: Multiple Vulnerabilities in the IOS FTP Server

9 May 2007

      -----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Cisco Security Advisory: Multiple Vulnerabilities in the IOS FTP
Server

Advisory ID: cisco-sa-20070509-iosftp

http://www.cisco.com/warp/public/707/cisco-sa-20070509-iosftp.shtml

Revision 1.0

For Public Release 2007 May 09 1600 UTC (GMT)

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

Contents
========

    Summary
    Affected Products
    Details
    Vulnerability Scoring Details
    Impact
    Software Version and 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 IOS File Transfer
Protocol (FTP) Server feature. These vulnerabilities include Denial
of Service, improper verification of user credentials and the ability
to read or write any file in the device's filesystem, including the
device's saved configuration, which may include passwords or other
sensitive information.

The IOS FTP Server is an optional service that is disabled by
default. Devices that are not specifically configured to enable the
IOS FTP Server service are unaffected by these vulnerabilities.

This vulnerability does not apply to the IOS FTP Client feature.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20070509-iosftp.shtml

Affected Products
=================

Vulnerable Products
+------------------

Cisco devices running IOS and configured for FTP server functionality
are affected by these issues.

IOS versions based on 11.3, 12.0, 12.1, 12.2, 12.3 and 12.4 contain
the IOS FTP server feature. The IOS FTP server feature was removed
via CSCsg16908.

Only certain IOS releases based on the above IOS trains contain the
IOS FTP server feature. For a device running Cisco IOS to be
vulnerable, the following command must be present in the device
configuration:

    ftp-server enable

Products Confirmed Not Vulnerable
+--------------------------------

Cisco devices that do not run IOS are not affected.

Cisco IOS devices that do not have the FTP server feature enabled are
not affected.

Cisco IOS XR is not affected.

No other Cisco devices are known to be affected.

Details
=======

Multiple vulnerabilities were discovered in the operation of the IOS
FTP Server feature. They are documented as Cisco bug IDs:

  * CSCek55259 - Improper authorization checking in IOS FTP server
  * CSCse29244 - IOS reload when transferring files via FTP

Due to the above issues with the IOS FTP server, the feature is being
removed. Cisco is considering adding more fully-featured and secure
FTP server functionality at a later date.

The IOS FTP Server feature removal is addressed with Cisco bug ID
CSCsg16908.

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:

CSCek55259 - Improper authorization checking in IOS FTP server

CVSS Base Score: 10.0
    Access Vector: Remote
    Access Complexity: Low
    Authentication: Not Required
    Confidentiality Impact: Complete
    Integrity Impact: Complete
    Availability Impact: Complete
    Impact Bias: Normal

CVSS Temporal Score: 8.3
    Exploitability: Functional
    Remediation Level: Official-Fix
    Report Confidence: Confirmed

CSCse29244 - IOS reload when transferring files via FTP

CVSS Base Score: 2.0
    Access Vector: Remote
    Access Complexity: Low
    Authentication: Required
    Confidentiality Impact: None
    Integrity Impact: None
    Availability Impact: Complete
    Impact Bias: Normal

CVSS Temporal Score: 1.7
    Exploitability: Functional
    Remediation Level: Official-Fix
    Report Confidence: Confirmed

Impact
======

Successful exploitation of these vulnerabilities may result in
unauthorized users accessing the filesystem on the IOS device, a
device restart, or remote code execution.

Unauthorized users could retrieve or write the device's
startup-config from the filesystem, which may contain information
that could enable privilege escalation.

Repeated exploitation of the vulnerabilities could lead to an
extended Denial of Service (DoS).

Software Version and 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.

Each row of the Cisco IOS software table (below) describes a release
train. If a given release train is vulnerable, then the earliest
possible releases that contain the fix (the "First Fixed Release")
and the anticipated date of availability for each are listed in the
"Rebuild" and "Maintenance" columns. A device running a release in
the given train that is earlier than the release in a specific column
(less than the First Fixed Release) is known to be vulnerable. The
release should be upgraded at least to the indicated release or a
later version (greater than or equal to the First Fixed Release
label).

Software releases that are not listed in the below table are not
affected.

For more information on the terms "Rebuild" and "Maintenance," consult
the following URL: http://www.cisco.com/warp/public/620/1.html

+---------------------------------------+
|    Major     |    Availability of     |
|   Release    |   Repaired Releases    |
|--------------+------------------------|
| Affected     |          |             |
| 12.0-Based   | Rebuild  | Maintenance |
| Release      |          |             |
|--------------+------------------------|
| 12.0         | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.0T        | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.0XC       | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.0XK       | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.0WC       | 12.0(5)  |             |
|              | WC17     |             |
|--------------+----------+-------------|
| Affected     |          |             |
| 12.1-Based   | Rebuild  | Maintenance |
| Release      |          |             |
|--------------+------------------------|
| 12.1         | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.1T        | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.1XH       | Vulnerable; migrate to |
|              | 12.2(40a) or later     |
|--------------+------------------------|
| 12.1XM       | Vulnerable; migrate to |
|              | 12.3(21)or later       |
|--------------+------------------------|
| Affected     |          |             |
| 12.2-Based   | Rebuild  | Maintenance |
| Release      |          |             |
|--------------+----------+-------------|
| 12.2         | 12.2     | 12.2(46)    |
|              | (40a)    |             |
|--------------+------------------------|
| 12.2T        | Vulnerable; migrate to |
|              | 12.3(21) or later      |
|--------------+------------------------|
| 12.2XA       | Vulnerable; migrate to |
|              | 12.3(21) or later      |
|--------------+------------------------|
| 12.2XG       | Vulnerable; migrate to |
|              | 12.3(21) or later      |
|--------------+------------------------|
| 12.2XT       | Vulnerable; migrate to |
|              | 12.3(21) or later      |
|--------------+------------------------|
| 12.2ZF       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.2ZH       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.2ZJ       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.2ZL       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.2ZN       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| Affected     |          |             |
| 12.3-Based   | Rebuild  | Maintenance |
| Release      |          |             |
|--------------+----------+-------------|
| 12.3         |          | 12.3(21)    |
|--------------+------------------------|
| 12.3B        | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3T        | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3TPC      | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3XA       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3XC       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3XD       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3XE       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3XF       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3XG       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3XH       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3XK       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3XQ       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3XR       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3XS       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3XX       | 12.3(8)  |             |
|              | XX2d     |             |
|--------------+------------------------|
| 12.3YA       | Vulnerable; migrate to |
|              | 12.4(12) or later      |
|--------------+------------------------|
| 12.3YD       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YG       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YH       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YI       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YK       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YM       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| 12.3YS       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YT       | Vulnerable; migrate to |
|              | 12.4(11)T or later     |
|--------------+------------------------|
| 12.3YZ       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
| Affected     |          |             |
| 12.4-Based   | Rebuild  | Maintenance |
| Release      |          |             |
|--------------+----------+-------------|
|              | 12.4     |             |
|              | (10b)    |             |
|              |----------+-------------|
| 12.4         | 12.4(3g) |             |
|              |----------+-------------|
|              | 12.4(7d) |             |
|              |----------+-------------|
|              | 12.4(8c) | 12.4(12)    |
|--------------+------------------------|
| 12.4SW       | Vulnerable; contact    |
|              | TAC                    |
|--------------+------------------------|
|              | 12.4(4)  |             |
|              | T6       |             |
|              |----------+-------------|
| 12.4T        | 12.4(6)  |             |
|              | T6       |             |
|              |----------+-------------|
|              | 12.4(9)  | 12.4(11)T   |
|              | T2       |             |
|--------------+------------------------|
| 12.4XA       | Vulnerable; migrate to |
|              | 12.4(6)T6 or later     |
|--------------+------------------------|
| 12.4XC       | 12.4(4)  |             |
|              | XC6      |             |
|--------------+----------+-------------|
| 12.4XD       | 12.4(4)  |             |
|              | XD4      |             |
|--------------+----------+-------------|
| 12.4XE       | 12.4(6)  |             |
|              | XE2      |             |
+---------------------------------------+

Workarounds
===========

Customers may disable the use of the IOS FTP Server feature by adding
the following command to the device configuration:

    no ftp-server enable

Additional mitigations that can be deployed on Cisco devices within
the network are available in the Cisco Applied Intelligence companion
document for this advisory:

http://www.cisco.com/warp/public/707/cisco-air-20070509-iosftp.shtml

Alternative File Transfer Mechanisms
+-----------------------------------

Cisco IOS supports multiple methods for transferring files to and
from the device. One such method is Secure Copy (SCP). SCP is
supported on Cisco IOS images that support strong cryptography. More
information on the SCP feature can be found at the following url:

http://www.cisco.com/en/US/products/s6350/products_configuration_guide_chapt...

Another alternative is using the Trivial File Transfer Protocol
(TFTP) server in IOS. Information on configuring the TFTP server can
be found here:

http://www.cisco.com/en/US/products/sw/iosswrel/ps1835/products_configuratio...

If disabling the IOS FTP Server is not feasible, customers may limit
FTP access to the device via one of several mechanisms detailed
below.

Infrastructure ACLs (iACL)
+-------------------------

Although it is often difficult to block traffic transiting your
network, it is possible to identify traffic which should never be
allowed to target your infrastructure devices and block that traffic
at the border of your network. Infrastructure ACLs are considered a
network security best practice and should be considered as a
long-term addition to good network security as well as a workaround
for this specific vulnerability. The ACL example shown below should
be included as part of the deployed infrastructure access-list which
will protect all devices with IP addresses in the infrastructure IP
address range.

A sample access list for devices running Cisco IOS is below:

    !--- Permit FTP services from trusted hosts destined 
    !--- to infrastructure addresses.

    access-list 150 permit tcp TRUSTED_HOSTS MASK INFRASTRUCTURE_ADDRESSES MASK eq 21
    access-list 150 permit tcp TRUSTED_HOSTS MASK INFRASTRUCTURE_ADDRESSES MASK eq 20

    !--- Deny FTP packets from all other sources destined to infrastructure addresses.

    access-list 150 deny   tcp any INFRASTRUCTURE_ADDRESSES MASK eq 21
    access-list 150 deny   tcp any INFRASTRUCTURE_ADDRESSES MASK eq 20

    !--- Permit all other traffic to transit the device.

    access-list 150 permit IP any any

    interface serial 2/0
      ip access-group 150 in

The white paper entitled "Protecting Your Core: Infrastructure
Protection Access Control Lists" presents guidelines and recommended
deployment techniques for infrastructure protection access lists.
This white paper can be obtained here:
http://www.cisco.com/warp/public/707/iacl.html

Receive ACLs (rACL)
+------------------

For distributed platforms, Receive ACLs may be an option starting in
Cisco IOS Software Versions 12.0(21)S2 for the 12000 (GSR), 12.0(24)S
for the 7500, and 12.0(31)S for the 10720. The Receive ACL protects
the device from harmful traffic before the traffic can impact the
route processor. Receive ACLs are designed to only protect the device
on which it is configured. On the 12000, transit traffic is never
affected by a receive ACL. Because of this, the destination IP
address "any" used in the example ACL entries below only refer to the
router's own physical or virtual IP addresses. On the 7500 and 10720,
transit traffic with IP options set will be subject to the Receive
ACL and permitted or denied accordingly. Receive ACLs are considered
a network security best practice, and should be considered as a
long-term addition to good network security, as well as a workaround
for this specific vulnerability. The white paper entitled "GSR:
Receive Access Control Lists" will help you identify and allow
legitimate traffic to your device and deny all unwanted packets: 
http://www.cisco.com/warp/public/707/racl.html.

The following is the receive path ACL written to permit this type of
traffic from trusted hosts:

    !--- Permit FTP from trusted hosts allowed to the RP.

    access-list 151 permit tcp TRUSTED_ADDRESSES MASK any eq 21
    access-list 151 permit tcp TRUSTED_ADDRESSES MASK any eq 20

    !--- Deny FTP from all other sources to the RP.

    access-list 151 deny   tcp any any eq 21
    access-list 151 deny   tcp any any eq 20

    !--- Permit all other traffic to the RP.
    !--- according to security policy and configurations.

    access-list 151 permit ip any any

    !--- Apply this access list to the 'receive' path.

    ip receive access-list 151

Control Plane Policing (CoPP)
+----------------------------

The Control Plane Policing (CoPP) feature may be used to mitigate
these vulnerabilities. In the following example, only FTP traffic
from trusted hosts and with 'receive' destination IP addresses is
permitted to reach the route processor (RP).

It should be noted that dropping traffic from unknown or untrusted IP
addresses may affect hosts with dynamically assigned IP addresses
from connecting to the Cisco IOS device.

        access-list 152 deny   tcp TRUSTED_ADDRESSES MASK any eq 21
        access-list 152 deny   tcp TRUSTED_ADDRESSES MASK any eq 20
        access-list 152 permit tcp any any eq 20
        access-list 152 permit tcp any any eq 21
        access-list 152 deny    ip any any
        !
        class-map match-all COPP-KNOWN-UNDESIRABLE
         match access-group 152
        !
        !
        policy-map COPP-INPUT-POLICY
         class COPP-KNOWN-UNDESIRABLE
          drop
        !
        control-plane
         service-policy input COPP-INPUT-POLICY

In the above CoPP example, the ACL entries that match the exploit
packets with the "permit" action result in these packets being
discarded by the policy-map "drop" function, while packets that match
the "deny" action are not affected by the policy-map drop function.

CoPP is available in Cisco IOS release trains 12.0S, 12.2SX, 12.2S,
12.3T, 12.4, and 12.4T.

Additional information on the configuration and use of the CoPP
feature can be found at the following URL:

http://www.cisco.com/en/US/products/ps6642/products_white_paper0900aecd804fa...

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.

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.

Exploitation and Public Announcements
=====================================

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

This vulnerability was reported to Cisco by a customer.

Status of this Notice: FINAL
============================

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.

Distribution
============

This advisory is posted on Cisco's worldwide website at:
http://www.cisco.com/warp/public/707/cisco-sa-20070509-iosftp.shtml

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 History
================

+---------------------------------------+
| Revision |             | Initial      |
| 1.0      | 2007-May-09 | public       |
|          |             | release      |
+---------------------------------------+

Cisco Security Procedures
=========================

Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and
registering to receive security information from Cisco, is available
on Cisco's worldwide website at
http://www.cisco.com/en/US/products/products_security_vulnerability_policy.h....
This includes instructions for press inquiries regarding Cisco
security notices.  All Cisco security advisories are available at
http://www.cisco.com/go/psirt.

- ---------------------------------------------------------------------
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.5 (SunOS)

iD8DBQFGQdbf8NUAbBmDaxQRAm0NAJ9Afj7rEDMQO+PolVME5taZE4R37ACfRGhS
coBHHAO2nUFEBFKxuUDJH4Q=
=phUK
-----END PGP SIGNATURE-----

Cisco Security Advisory: Multiple Vulnerabilities in the IOS FTP Server

Cisco Systems Product Security Incident Response Team