Cisco FXOS and NX-OS Software Authenticated Simple Network Management Protocol Denial of Service Vulnerability

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Updated:August 28, 2019
Document ID:1567011295275306

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Cisco Security Advisory

Cisco FXOS and NX-OS Software Authenticated Simple Network Management Protocol Denial of Service Vulnerability

High
Advisory ID:
cisco-sa-20190828-fxnxos-snmp-dos
First Published:
2019 August 28 16:00 GMT
Last Updated: 
2019 October 8 14:45 GMT
Version 1.1:
Final
Workarounds:
No workarounds available
CVE-2019-1963
CWE-20
CVSS Score:
Base 7.7Click Icon to Copy Verbose Score
CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
CVE-2019-1963
CWE-20

Summary

  • 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://sec.cloudapps.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.

Affected Products

  • Vulnerable Products

    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:

    • Firepower 4100 Series
    • Firepower 9300 Security Appliances
    • MDS 9000 Series Multilayer Switches
    • Nexus 1000 Virtual Edge for VMware vSphere
    • Nexus 1000V Switch for Microsoft Hyper-V
    • Nexus 1000V Switch for VMware vSphere
    • Nexus 3000 Series Switches
    • Nexus 3500 Platform Switches
    • Nexus 3600 Platform Switches
    • Nexus 5500 Platform Switches
    • Nexus 5600 Platform Switches
    • Nexus 6000 Series Switches
    • Nexus 7000 Series Switches
    • Nexus 7700 Series Switches
    • Nexus 9000 Series Fabric Switches in Application Centric Infrastructure (ACI) mode
    • Nexus 9000 Series Switches in standalone NX-OS mode
    • Nexus 9500 R-Series Switching Platform
    • UCS 6200 Series Fabric Interconnects
    • UCS 6300 Series Fabric Interconnects
    • UCS 6400 Series Fabric Interconnects

    For information about which Cisco FXOS and NX-OS Software releases are vulnerable, see the Fixed Software section of this advisory.

    Determine the Status of SNMP

    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. 

    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

    Products Confirmed Not Vulnerable

    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.

Details

  • 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.

Workarounds

  • There are no workarounds that address this vulnerability.

    Mitigation for Cisco NX-OS Software

    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.

Fixed Software

  • 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.

    Fixed Releases

    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
    2. The 7.0(3)I4 code train is not applicable to Nexus 3500 Platform Switches.

    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)

    Additional Resources

    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.

    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

    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.

Exploitation and Public Announcements

  • 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

  • This vulnerability was found during internal security testing.

Cisco Security Vulnerability Policy

  • 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.

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Revision History

  • 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
    Show Less

Cisco Security Vulnerability Policy

  • 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

Related to This Advisory