ESB-2017.1644.2 - UPDATE [Appliance] Cisco IOS and IOS XE Software: Multiple vulnerabilities 2017-07-17

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             AUSCERT External Security Bulletin Redistribution

                              ESB-2017.1644.2
SNMP Remote Code Execution Vulnerabilities in Cisco IOS and IOS XE Software
                               17 July 2017

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        AusCERT Security Bulletin Summary
        ---------------------------------

Product:           Cisco IOS and IOS XE Software
Publisher:         Cisco Systems
Operating System:  Network Appliance
Impact/Access:     Root Compromise   -- Existing Account
                   Denial of Service -- Existing Account
Resolution:        Patch/Upgrade
CVE Names:         CVE-2017-6744 CVE-2017-6743 CVE-2017-6742
                   CVE-2017-6741 CVE-2017-6740 CVE-2017-6739
                   CVE-2017-6738 CVE-2017-6737 CVE-2017-6736

Original Bulletin: 
   https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170629-snmp

Revision History:  July 17 2017: Indicated that fixed software is 
                                 available.
                   June 30 2017: Initial Release

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SNMP Remote Code Execution Vulnerabilities in Cisco IOS and IOS XE Software

High
Advisory ID:  cisco-sa-20170629-snmp
First Published: 2017 June 29 16:00  GMT
Last Updated:  2017 July 12 18:18  GMT
Version 1.4:  Interim
Workarounds:  Yes

Cisco Bug IDs:
CSCsy56638
CSCve54313
CSCve57697

CVSS Score:
Base 8.8, Temporal 8.2
Base 8.8, Temporal 8.2
CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C

CVE-2017-6736
CVE-2017-6737
CVE-2017-6738
CWE-119

Summary
The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and
IOS XE Software contains multiple vulnerabilities that could allow an
authenticated, remote attacker to remotely execute code on an affected
system or cause an affected system to reload. An attacker could exploit
these vulnerabilities by sending a crafted SNMP packet to an affected
system via IPv4 or IPv6. Only traffic directed to an affected system can
be used to exploit these vulnerabilities.

The vulnerabilities are due to a buffer overflow condition in the SNMP
subsystem of the affected software. The vulnerabilities affect all versions
of SNMP - Versions 1, 2c, and 3. To exploit these vulnerabilities via SNMP
Version 2c or earlier, the attacker must know the SNMP read-only community
string for the affected system. To exploit these vulnerabilities via
SNMP Version 3, the attacker must have user credentials for the affected
system. A successful exploit could allow the attacker to execute arbitrary
code and obtain full control of the affected system or cause the affected
system to reload.

Customers are advised to apply the workaround as contained in the Workarounds
section below. Fixed software information is available via the Cisco IOS
Software Checker. All devices that have enabled SNMP and have not explicitly
excluded the affected MIBs or OIDs should be considered vulnerable.

Cisco has released software updates that address these vulnerabilities. There
are workarounds that address these vulnerabilities.

This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170629-snmp

Affected Products

Vulnerable Products

These vulnerabilities affect all releases of Cisco IOS and IOS XE
Software prior to the first fixed release and they affect all versions of
SNMP—Versions 1, 2c, and 3.

Devices configured with any of the following MIBs are vulnerable:

ADSL-LINE-MIB
ALPS-MIB
CISCO-ADSL-DMT-LINE-MIB
CISCO-BSTUN-MIB
CISCO-MAC-AUTH-BYPASS-MIB
CISCO-SLB-EXT-MIB
CISCO-VOICE-DNIS-MIB
CISCO-VOICE-NUMBER-EXPANSION-MIB
TN3270E-RT-MIB
All of the MIBs listed above are enabled by default when SNMP is
enabled. Some of the MIBs may not be present on all systems or versions
but are enabled when present.

Administrators may be accustomed to utilizing the show snmp mib command in
privileged EXEC mode to display a list of enabled MIBs on a device. Not all
of the MIBs will be displayed in the output of the show snmp mib command
but may still be enabled. Customers are advised to implement the entire
exclude list as detailed in the Workarounds section of the advisory.
Determining the Cisco IOS Software Release
To determine which Cisco IOS Software release is running on a device,
administrators can log in to the device, use the show version command in
the CLI, and then refer to the system banner that appears. If the device
is running Cisco IOS Software, the system banner displays text similar to
Cisco Internetwork Operating System Software or Cisco IOS Software. The
banner also displays the installed image name in parentheses, followed by
the Cisco IOS Software release number and release name. Some Cisco devices
do not support the show version command or may provide different output.

The following example identifies a Cisco product that is running
Cisco IOS Software Release 15.5(2)T1 with an installed image name of
C2951-UNIVERSALK9-M:

Router> show version

Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1,
RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Mon 22-Jun-15 09:32 by prod_rel_team
.
.
.
For information about the naming and numbering conventions for Cisco
IOS Software releases, see White Paper: Cisco IOS and NX-OS Software
Reference Guide.

Determining the Cisco IOS XE Software Release
To determine which Cisco IOS XE Software release is running on a device,
administrators can log in to the device, use the show version command in
the CLI, and then refer to the system banner that appears. If the device
is running Cisco IOS XE Software, the system banner displays Cisco IOS XE
Software or similar text.

The following example shows the output of the show version command on a
device that is running Cisco IOS XE Software Release 3.16.1aS:

Router> show version

Cisco IOS XE Software, Version 03.16.01a.S - Extended Support Release
Cisco IOS Software, ASR1000 Software (PPC_LINUX_IOSD-ADVENTERPRISEK9-M),
Version 15.5(3)S1a, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2015 by Cisco Systems, Inc.
Compiled Wed 04-Nov-15 17:40 by mcpre
.
.
.
For information about the naming and numbering conventions for Cisco
IOS XE Software releases, see White Paper: Cisco IOS and NX-OS Software
Reference Guide.

Products Confirmed Not Vulnerable

No other Cisco products are currently known to be affected by these
vulnerabilities.
Details
The Simple Network Management Protocol (SNMP) is an application-layer
protocol that provides a standardized framework and a common language for
monitoring and managing devices in a network. It defines a message format
for communication between SNMP managers and agents.

An SNMP agent gathers data from the SNMP MIB, which is the repository of
information about device parameters and network data. It also responds to
requests from an SNMP manager to get or set data. An SNMP agent contains
MIB variables whose values can be requested or changed by an SNMP manager
via get or set operations.

These vulnerabilities affect all versions of SNMP—Versions 1, 2c, and
3. An attacker could exploit these vulnerabilities by sending a crafted
SNMP packet to an affected device via IPv4 or IPv6. Only traffic directed
to the affected system can be used to exploit these vulnerabilities.

To exploit these vulnerabilities via SNMP Version 2c or earlier, the
attacker must know the SNMP read-only community string for the affected
system. A community string is a password that is applied to a device to
restrict both read-only and read-write access to the SNMP data on the
device. These community strings, as with all passwords, should be chosen
carefully to ensure they are not trivial. They should also be changed at
regular intervals and in accordance with network security policies. For
example, the strings should be changed when a network administrator changes
roles or leaves the organization.

To exploit these vulnerabilities via SNMP Version 3, the attacker must
have user credentials for the affected system.

Indicators of Compromise
Exploitation of these vulnerabilities will cause an affected device to
reload and generate a crashinfo file. Contact the Cisco Technical Assistance
Center (TAC) to review the file and determine whether the device has been
compromised by exploitation of these vulnerabilities.
Workarounds
Administrators are advised to allow only trusted users to have SNMP access
on an affected system. Administrators are also advised to monitor affected
systems by using the show snmp host command in the CLI.

In addition, administrators can mitigate these vulnerabilities by disabling
the following MIBs on a device:

ADSL-LINE-MIB
ALPS-MIB
CISCO-ADSL-DMT-LINE-MIB
CISCO-BSTUN-MIB
CISCO-MAC-AUTH-BYPASS-MIB
CISCO-SLB-EXT-MIB
CISCO-VOICE-DNIS-MIB
CISCO-VOICE-NUMBER-EXPANSION-MIB
TN3270E-RT-MIB
To create or update a view entry and disable the affected MIBs,
administrators can use the snmp-server view global configuration command,
as shown in the following example:

!Standard VIEW and Security Exclusions
snmp-server view NO_BAD_SNMP iso included
snmp-server view NO_BAD_SNMP internet included
snmp-server view NO_BAD_SNMP snmpUsmMIB excluded
snmp-server view NO_BAD_SNMP snmpVacmMIB excluded
snmp-server view NO_BAD_SNMP snmpCommunityMIB excluded
snmp-server view NO_BAD_SNMP ciscoMgmt.252 excluded
!End Standard View

!Advisory Specific Mappings
!ADSL-LINE-MIB
snmp-server view NO_BAD_SNMP transmission.94 excluded

!TN3270E-RT-MIB
snmp-server view NO_BAD_SNMP mib-2.34.9 excluded

!CISCO-BSTUN-MIB
snmp-server view NO_BAD_SNMP ciscoMgmt.35 excluded

!ALPS-MIB
snmp-server view NO_BAD_SNMP ciscoMgmt.95 excluded

!CISCO-ADSL-DMT-LINE-MIB
snmp-server view NO_BAD_SNMP ciscoMgmt.130 excluded

!CISCO-VOICE-DNIS-MIB
snmp-server view NO_BAD_SNMP ciscoMgmt.219 excluded

!CISCO-SLB-EXT-MIB
snmp-server view NO_BAD_SNMP ciscoMgmt.254 excluded

!CISCO-MAC-AUTH-BYPASS-MIB
snmp-server view NO_BAD_SNMP ciscoMabMIB excluded

!CISCO-VOICE-NUMBER-EXPANSION-MIB
snmp-server view NO_BAD_SNMP ciscoExperiment.997 excluded
To then apply this configuration to a community string, administrators
can use the following command:

 snmp-server community mycomm view NO_BAD_SNMP RO
For SNMP Version 3, administrators can use the following command:

 snmp-server group v3group auth read NO_BAD_SNMP write NO_BAD_SNMP
Fixed Software
Cisco has released free software updates that address the vulnerabilities
described in this advisory. Customers may only install and expect support
for software versions and feature sets for which they have purchased a
license. By installing, downloading, accessing, or otherwise using such
software upgrades, customers agree to follow the terms of the Cisco
software license:
http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html

Additionally, customers may only download software for which they have a
valid license, procured from Cisco directly, or through a Cisco authorized
reseller or partner. In most cases this will be a maintenance upgrade to
software that was previously purchased. Free security software updates
do not entitle customers to a new software license, additional software
feature sets, or major revision upgrades.

When considering software upgrades, customers are advised to regularly
consult the advisories for Cisco products, which are available from the
Cisco Security Advisories and Alerts page, to determine exposure and a
complete upgrade solution.

In all cases, customers should ensure that the devices to be upgraded
contain sufficient memory and confirm that current hardware and software
configurations will continue to be supported properly by the new release. If
the information is not clear, customers are advised to contact the Cisco
Technical Assistance Center (TAC) or their contracted maintenance providers.

Customers Without Service Contracts

Customers who purchase directly from Cisco but do not hold a Cisco service
contract and customers who make purchases through third-party vendors but
are unsuccessful in obtaining fixed software through their point of sale
should obtain upgrades by contacting the Cisco TAC:
http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html

Customers should have the product serial number available and be prepared
to provide the URL of this advisory as evidence of entitlement to a free
upgrade.

Cisco IOS and IOS XE Software
To help customers determine their exposure to vulnerabilities in Cisco IOS
and IOS XE Software, Cisco provides a tool, the Cisco IOS Software Checker,
that identifies any Cisco Security Advisories that impact a specific software
release and the earliest release that fixes the vulnerabilities described
in each advisory (“First Fixed”). If applicable, the tool also returns
the earliest release that fixes all the vulnerabilities described in all
the advisories identified (“Combined First Fixed”).

Customers can use this tool to perform the following tasks:

Initiate a search by choosing one or more releases from a drop-down menu
or uploading a file from a local system for the tool to parse
Enter the output of the show version command for the tool to parse
Create a custom search by including all previously published Cisco Security
Advisories, a specific advisory, or all advisories in the most recent
bundled publication
To determine whether a release is affected by any published Cisco Security
Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco
IOS Software or Cisco IOS XE Software release—for example, 15.1(4)M2 or
3.1.4S—in the following field:

For a mapping of Cisco IOS XE Software releases to Cisco IOS Software
releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S
Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco
IOS XE Software release.

Exploitation and Public Announcements
Cisco is aware of external knowledge of these vulnerabilities. As a
precaution, we are notifying customers about the potential for exploitation.

Source
These vulnerabilities were found during internal testing.

URL
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170629-snmp
Revision History

   
  Version  Description                                                                                                                                                                                                                                                                                                                                                                                                                            Section                           Status    Date
      1.4  Indicated that fixed software is available. Added links to the Cisco IOS Software Checker.                                                                                                                                                                                                                                                                                                                                             Summary, Fixed Software           Interim   2017-July-12
      1.3  Added OVAL definitions.                                                                                                                                                                                                                                                                                                                                                                                                                Header                            Interim   2017-July-07
      1.2  Added statement regarding fixed software and workarounds to the Summary section. Removed information regarding the Cisco IOS Software Checker. The tool is currently experiencing  issues and returning inconsistent results to customer queries.                                                                                                                                                                                      Summary, Fixed Software           Interim   2017-July-06
      1.1  Added Statement to Vulnerable Products to indicate that all affected MIBs are enabled by default on affected versions and hardware configurations if SNMP is enabled. Updated information in Vulnerable Products to indicate that the 'show snmp mib' command was insufficient to determine if a device is affected. Added comments to the Workaround configuration commands to document which exclusions tie to the vulnerable MIBs.  Vulnerable Products, Workarounds  Interim   2017-July-03
      1    Initial public release.                                                                                                                                                                                                                                                                                                                                                                                                                                                  Interim   2017-June-29
    


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