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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
18 April 2019
===========================================================================
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: April 18 2019: Vendor advises of public exploitation
June 30 2017: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
SNMP Remote Code Execution Vulnerabilities in Cisco IOS and IOS XE Software
Priority: High
Advisory ID: cisco-sa-20170629-snmp
First Published: 2017 June 29 16:00 GMT
Last Updated: 2019 April 17 18:59 GMT
Version 1.7: Final
Workarounds: Yes
Cisco Bug IDs: CSCsy56638 CSCve54313 CSCve57697 CSCve60276CSCve60376 CSCve60402
CSCve60507 CSCve66540CSCve66601 CSCve66658 CSCve78027 CSCve89865
CVE-2017-6736 CVE-2017-6737 CVE-2017-6738 CVE-2017-6739
CVE-2017-6740 CVE-2017-6741 CVE-2017-6742 CVE-2017-6743
CVE-2017-6744
CWE-119
CVSS Score:
8.8, Temporal 8.2AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
Summary
o 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
o 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
o 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
o 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
o 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
o 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:
[ ] [Check]
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
o At the time of initial publication, Cisco was aware of external knowledge
of the vulnerabilities described in this advisory and, as a precaution,
notified customers about the potential for exploitation.
On January 6, 2017, a security researcher published functional exploit code
for these vulnerabilities.
The Cisco Product Security Incident Response Team (PSIRT) is aware of
exploitation of the vulnerabilities that are described in this advisory.
Additional information can be found at Cisco TALOS: DNS Hijacking Abuses
Trust In Core Internet Service
Source
o These vulnerabilities were found during internal testing.
Cisco Security Vulnerability Policy
o To learn about Cisco security vulnerability disclosure policies and
publications, see the Security Vulnerability Policy . This document also
contains instructions for obtaining fixed software and receiving security
vulnerability information from Cisco.
Action Links for This Advisory
o Snort Rule 43424
Snort Rule 43425
Snort Rule 43426
Snort Rule 43427
Snort Rule 43428
Snort Rule 43429
Snort Rule 43430
Snort Rule 43431
Snort Rule 43432
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Cisco IOS and IOS-XE SNMP Remote Code Execution
Show All 18...
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-20170629-snmp
Revision History
o +---------+-------------------+---------------+---------+-----------------+
| Version | Description | Section | Status | Date |
+---------+-------------------+---------------+---------+-----------------+
| | Updated the | | | |
| | Exploitation and | | | |
| | Public | Exploitation | | |
| 1.7 | Announcements | and Public | Final | 2019-April-17 |
| | section with | Announcements | | |
| | information on | | | |
| | public | | | |
| | exploitation. | | | |
+---------+-------------------+---------------+---------+-----------------+
| | Added information | Exploitation | | |
| 1.6 | about public | and Public | Final | 2018-January-11 |
| | exploit | Announcements | | |
| | availability. | | | |
+---------+-------------------+---------------+---------+-----------------+
| | Re-added Cisco | | | |
| 1.5 | Bug ID CSCve60507 | Cisco Bug IDs | Interim | 2017-July-22 |
| | to bug list. | | | |
+---------+-------------------+---------------+---------+-----------------+
| | Indicated that | | | |
| | fixed software is | Summary, | | |
| 1.4 | available. Added | Fixed | Interim | 2017-July-12 |
| | links to the | Software | | |
| | Cisco IOS | | | |
| | Software Checker. | | | |
+---------+-------------------+---------------+---------+-----------------+
| 1.3 | Added OVAL | Header | Interim | 2017-July-07 |
| | definitions. | | | |
+---------+-------------------+---------------+---------+-----------------+
| | Added statement | | | |
| | regarding fixed | | | |
| | software and | | | |
| | workarounds to | | | |
| | the Summary | | | |
| | section. Removed | | | |
| | information | | | |
| | regarding the | Summary, | | |
| 1.2 | Cisco IOS | Fixed | Interim | 2017-July-06 |
| | Software Checker. | Software | | |
| | The tool is | | | |
| | currently | | | |
| | experiencing | | | |
| | issues and | | | |
| | returning | | | |
| | inconsistent | | | |
| | results to | | | |
| | customer queries. | | | |
+---------+-------------------+---------------+---------+-----------------+
| | 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 | Vulnerable | | |
| 1.1 | Products to | Products, | Interim | 2017-July-03 |
| | indicate that the | Workarounds | | |
| | '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. | | | |
+---------+-------------------+---------------+---------+-----------------+
| 1.0 | Initial public | - | Interim | 2017-June-29 |
| | release. | | | |
+---------+-------------------+---------------+---------+-----------------+
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