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AUSCERT External Security Bulletin Redistribution
ESB-2018.0907
Cisco IOS Software Simple Network Management Protocol GET
MIB Object ID Denial of Service Vulnerability
29 March 2018
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Existing Account
Resolution: Patch/Upgrade
CVE Names: CVE-2018-0161
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-snmp
- --------------------------BEGIN INCLUDED TEXT--------------------
Cisco Security Advisory
Cisco IOS Software Simple Network Management Protocol GET MIB Object ID Denial
of Service Vulnerability
High
Advisory ID: cisco-sa-20180328-snmp
First Published: 2018 March 28 16:00 GMT
Version 1.0: Final
Workarounds: Yes
Cisco Bug IDs:
CSCvd89541
CVE-2018-0161
CWE-399
CVSSÂ Score:
7.7 AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
Summary
o A vulnerability in the Simple Network Management Protocol (SNMP) subsystem
of Cisco IOS Software running on certain models of Cisco Catalyst Switches
could allow an authenticated, remote attacker to cause a denial of service
(DoS) condition.
The vulnerability is due to a condition that could occur when the affected
software processes an SNMP read request that contains a request for the
ciscoFlashMIB object ID (OID). An attacker could trigger this vulnerability
by issuing an SNMP GET request for the ciscoFlashMIB OID on an affected
device. A successful exploit could cause the affected device to restart due
to a SYS-3-CPUHOG.
Cisco has released software updates that address this vulnerability. There
are workarounds that address this vulnerability.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-20180328-snmp
This advisory is part of the March 28, 2018, release of the Cisco IOS and
IOS XE Software Security Advisory Bundled Publication, which includes 20
Cisco Security Advisories that describe 22 vulnerabilities. For a complete
list of the advisories and links to them, see Cisco Event Response: March
2018 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled
Publication.
Affected Products
o Vulnerable Products
This vulnerability affects the following Cisco devices if they are running
a vulnerable release of Cisco IOS Software and are configured to use SNMP
Version 2 (SNMPv2) or SNMP Version 3 (SNMPv3):
Cisco Catalyst 2960-L Series Switches
Cisco Catalyst Digital Building Series Switches - 8P
Cisco Catalyst Digital Building Series Switches - 8U
For information about which Cisco IOS Software releases are vulnerable, see
the Fixed Software section of this advisory.
To determine whether a device is configured to use SNMP, administrators can
use the show running-config | include snmp-server privileged EXEC command
in the CLI of the device. If the command returns a line that contains
snmp-server community or snmp-server user, the device is vulnerable, as
shown in the following examples.
SNMPv2:
snmp-server community example ro
SNMPv3:
snmp-server user example example-snmp v3
snmp-server group example-snmp v3 noauth
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 shows the output of the command for a device that is
running Cisco IOS Software Release 15.5(2)T1 and has 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 the Cisco IOS and NX-OS Software Reference Guide.
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by this
vulnerability.
Cisco has confirmed that this vulnerability does not affect Cisco IOS XE
Software, Cisco IOS XR Software, or Cisco NX-OS Software.
Indicators of Compromise
o Exploitation of this vulnerability typically results in a crash in the SNMP
ENGINE process, as shown in the following example:
%SYS-3-CPUHOG: Task is running for (2012)msecs, more than (2000)msecs (0/0),process = SNMP ENGINE
Workarounds
o There are workarounds that address this vulnerability.
Use SNMP Access Control Lists
Note: Because the vulnerable feature uses UDP as a transport, it is
possible to spoof the sender's IP address, which may defeat access control
lists (ACLs) that permit communication to these ports from trusted IP
addresses. Unicast Reverse Path Forwarding (RPF) should be considered for
use in conjunction with UDP to offer a better mitigation solution. The
following is an example of an ACL that allows only hosts at 192.168.0.1 to
query the device with SNMP requests:
access-list 1 permit 192.168.0.1
snmp-server community example RO 1
Exclude the Cisco Flash MIB from the SNMP Query list
SNMPv2:
snmp-server view example ciscoFlashMIB excluded
snmp-server community example view example ro
SNMPv3:
snmp-server user example example-snmp v3
snmp-server group example-snmp v3 noauth read example
snmp-server view example ciscoFlashMIB excluded
Fixed Software
o Cisco has released free software updates that address the vulnerability
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:
https://www.cisco.com/c/en/us/products/end-user-license-agreement.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:
https://www.cisco.com/c/en/us/support/web/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 Software
To help customers determine their exposure to vulnerabilities in Cisco IOS
Software, Cisco provides a tool, the Cisco IOS Software Checker, that
identifies any Cisco Security Advisories that impact a specific Cisco IOS
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
list 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 release--for example, 15.1(4)M2--in the following field:
[ ] [Check]
Exploitation and Public Announcements
o The Cisco Product Security Incident Response Team (PSIRT) is not aware of
any public announcements or malicious use of the vulnerability that is
described in this advisory.
Source
o This vulnerability was found while handling customer service requests.
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.
Subscribe to Cisco Security Notifications
o Subscribe
Related to This Advisory
o Cisco Event Response: March 2018 Semiannual Cisco IOS and IOS XE Software
Security Advisory Bundled Publication
Cisco Security Blog: Cisco IOS and IOS XE Software Bundled Publication
March 2018
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-snmp
Revision History
o
+----------+----------------------------+----------+---------+----------------+
| Version | Description | Section | Status | Date |
+----------+----------------------------+----------+---------+----------------+
| 1.0 | Initial public release. | -- | Final | 2018-March-28 |
+----------+----------------------------+----------+---------+----------------+
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