A vulnerability in the Simple Network Management Protocol (SNMP) input packet processor of Cisco FXOS Software and Cisco NX-OS Software could allow an authenticated, remote attacker to cause the SNMP application on an affected device to restart unexpectedly. The vulnerability is due to improper validation of Abstract Syntax Notation One (ASN.1)-encoded variables in SNMP packets. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the SNMP daemon on the affected device. A successful exploit could allow the attacker to cause the SNMP application to restart multiple times, leading to a system-level restart and a denial of service (DoS) condition. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190828-fxnxos-snmp-dos This advisory is part of the August 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication, which includes five Cisco Security Advisories that describe five vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: August 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.
A vulnerability in the Simple Network Management Protocol (SNMP) input packet processor of Cisco FXOS Software and Cisco NX-OS Software could allow an authenticated, remote attacker to cause the SNMP application on an affected device to restart unexpectedly.
The vulnerability is due to improper validation of Abstract Syntax Notation One (ASN.1)-encoded variables in SNMP packets. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the SNMP daemon on the affected device. A successful exploit could allow the attacker to cause the SNMP application to restart multiple times, leading to a system-level restart and a denial of service (DoS) condition.
Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190828-fxnxos-snmp-dos
This vulnerability affects the following Cisco products if they have SNMP configured and they are running a vulnerable release of Cisco FXOS or NX-OS Software:
For information about which Cisco FXOS and NX-OS Software releases are vulnerable, see the Fixed Software section of this advisory.
The following subsections describe how to determine whether SNMP is running on a device.
Determine the Status of SNMP for Cisco FXOS Software
Administrators can determine whether SNMP is running on a device by using the show configuration | include snmp command in the device CLI. If the command returns output, SNMP is configured.
fxos-switch# show configuration | include snmp
enable snmp
Determine the Status of SNMP for Cisco NX-OS Software
Administrators can determine whether SNMP is running on a device by using the show running-config snmp command in the device CLI. If the command returns output, SNMP is configured.
Vulmon
nxos-switch# show running-config snmp
.
.
.
snmp-server user admin network-admin auth md5 ***** priv ***** localizedkey
snmp-server community community-string group network-admin
Determine the Status of SNMP for Cisco UCS
Administrators can determine whether SNMP is running on a device by using the show configuration | grep snmp command in the device CLI. If the command returns output, SNMP is configured.
# show configuration | grep snmp
enable snmp
Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect Cisco Firepower 2100 Series.
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 for which values can be requested or changed by an SNMP manager by using get or set operations.
This vulnerability affects all versions of SNMP supported on the device-versions 1, 2c, and 3. An attacker could exploit this vulnerability by sending a specific SNMP packet to an affected device using IPv4 or IPv6. Only traffic directed to an affected system can be used to exploit this vulnerability. This vulnerability is not exploitable if the device is configured only to send SNMP traps.
To exploit this vulnerability by using 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 that 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 this vulnerability by using SNMP Version 3 (SNMPv3), the attacker must have SNMPv3 credentials for the affected system.
There are no workarounds that address this vulnerability.
As a mitigation for the vulnerability that is described in this advisory, administrators of systems that are running Cisco NX-OS Software can configure an access control list (ACL) on an SNMP community to filter incoming SNMP requests to ensure that SNMP polling is performed only by trusted SNMP clients. In the following example, the device will accept incoming SNMPv2c requests only from a single trusted host, 192.168.1.2:
switch# show access-list acl_for_snmp IPV4 ACL acl_for_snmp
10 permit udp 192.168.1.2/32 192.168.1.3/32 eq snmp
To implement the preceding ACL, administrators can add it to the snmp-server community configuration command:
switch# show running-config snmp !Command: show running-config snmp snmp-server community mycompany use-acl acl_for_snmp
For additional information about configuring ACLs to filter incoming SNMP requests, see Filtering SNMP Requests in the Cisco NX-OS Configuration Guide.
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 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.
Customers are advised to upgrade to an appropriate release as indicated in the applicable table in this section. To help ensure a complete upgrade solution, customers should consider that this advisory is part of a bundled publication. The following page provides a complete list of bundle advisories: Cisco Event Response: August 2019 Cisco FXOS and NX-OS Software Security Advisory Bundled Publication.
In the following table(s), the left column lists releases of Cisco FXOS Software or Cisco NX-OS Software. The center column indicates whether a release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all the vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.
Firepower 4100 Series and Firepower 9300 Security Appliances: CSCvn23536
| Cisco FXOS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 2.2 |
2.2.2.91 | 2.2.2.91 |
| 2.2 |
2.2.2.91 |
2.2.2.91 |
| 2.3 |
2.3.1.130 |
2.3.1.130 |
| 2.4 | 2.4.1.222 |
2.4.1.222 |
| 2.6 | Not vulnerable | Not vulnerable |
MDS 9000 Series Multilayer Switches: CSCvn23531
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| 5.2 |
6.2(29) |
6.2(29) |
| 6.2 |
6.2(29) |
6.2(29) |
| 7.3 | 8.3(2) | 8.4(1) |
| 8.1 |
8.3(2) |
8.4(1) |
| 8.2 | 8.3(2) |
8.4(1) |
| 8.3 |
8.3(2) | 8.4(1) |
| 8.4 | Not vulnerable | Not vulnerable |
Nexus 1000 Virtual Edge for VMware vSphere: CSCvn23532
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| 5.2 |
5.2(1)SV5(1.2) |
5.2(1)SV5(1.2) |
Nexus 1000V Switch for Microsoft Hyper-V: CSCvn23537
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 5.2 |
No fix at this time |
No fix at this time |
| 5.2 |
No fix at this time |
No fix at this time |
Nexus 1000V Switch for VMware vSphere: CSCvn23532
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 5.2 |
5.2(1)SV3(4.1a) | 5.2(1)SV3(4.1a) |
| 5.2 |
5.2(1)SV3(4.1a) |
5.2(1)SV3(4.1a) |
Nexus 3000 Series Switches, Nexus 3500 Platform Switches, and Nexus 9000 Series Switches in Standalone NX-OS Mode: CSCvn13270
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 7.0(3)I42 |
Not vulnerable |
7.0(3)I4(9)2 |
| 7.0(3)I42 | 7.0(3)I4(9)2 | 7.0(3)I4(9)2 |
| 7.0(3)I7 | 7.0(3)I7(6) |
7.0(3)I7(6) |
| 9.2 | 9.2(3) |
9.2(3) |
| 9.3 | Not vulnerable | Not vulnerable |
Nexus 3600 Platform Switches and Nexus 9500 R-Series Switching Platform: CSCvn13270
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| 7.0(3)F |
9.2(3) |
9.2(3) |
| 9.2 | 9.2(3) |
9.2(3) |
| 9.3 | Not vulnerable | Not vulnerable |
Nexus 5500 and 5600 Platform Switches and Nexus 6000 Series Switches: CSCvn23534
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 7.1 |
7.1(5)N1(1b) |
7.1(5)N1(1b) |
| 7.1 | 7.1(5)N1(1b) |
7.1(5)N1(1b) |
| 7.3 | 7.3(5)N1(1) |
7.3(5)N1(1) |
Nexus 7000 and 7700 Series Switches: CSCvn23531
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 6.2 |
6.2(22) |
6.2(22) |
| 6.2 |
6.2(22) |
6.2(22) |
| 7.2 | 7.3(4)D1(1) |
7.3(4)D1(1) |
| 7.3 | 7.3(4)D1(1) |
7.3(4)D1(1) |
| 8.0 | 8.2(3) |
8.2(3) |
| 8.1 | 8.2(3) |
8.2(3) |
| 8.2 | 8.2(3) | 8.2(3) |
| 8.3 | 8.3(2) |
8.4(1) |
| 8.4 |
Not vulnerable | Not vulnerable |
Nexus 9000 Series Fabric Switches in ACI Mode: CSCvn23529
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 13.1 |
13.2(7k) |
13.2(7k) |
| 13.1 |
13.2(7k) |
13.2(7k) |
| 13.2 | 13.2(7k) |
13.2(7k) |
| 14.0 | 14.0(2c) |
14.0(2c) |
| 14.1 | 14.1(1i) |
14.1(1i) |
UCS 6200, 6300, and 6400 Series Fabric Interconnects: CSCvn23535 and CSCvn23538
| Cisco NX-OS Software Release | First Fixed Release for This Vulnerability |
First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories |
|---|---|---|
| Earlier than 3.2 |
3.2(3l) |
3.2(3l) |
| 3.2 |
3.2(3l) | 3.2(3l) |
| 4.0 |
4.0(4e) |
4.0(4e) |
For help determining the best Cisco NX-OS Software release for a Cisco Nexus Switch, administrators can refer to the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.
For help determining the best Cisco NX-OS Software release for Cisco UCS, refer to the Recommended Releases documents in the release notes for the device.Cisco MDS Series Switches
Cisco Nexus 1000V for VMware Switch
Cisco Nexus 3000 Series and 3500 Series Switches
Cisco Nexus 5000 Series Switches
Cisco Nexus 5500 Platform Switches
Cisco Nexus 6000 Series Switches
Cisco Nexus 7000 Series Switches
Cisco Nexus 9000 Series Switches
Cisco Nexus 9000 Series ACI-Mode Switches
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.
This vulnerability was found during internal security testing.
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.
| Version | Description | Section | Status | Date |
|---|---|---|---|---|
| 1.1 | Updated the MDS and UCS fixed release tables. | Fixed Software | Final | 2019-October-08 |
| 1.0 | Initial public release. | - | Final | 2019-August-28 |
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