18 October 2018
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2018.3143 Cisco NX-OS Software Authenticated Simple Network Management Protocol Denial of Service Vulnerability 18 October 2018 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Cisco NX-OS Software Publisher: Cisco Systems Operating System: Cisco Impact/Access: Denial of Service -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2018-0456 Original Bulletin: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181017-nxos-snmp - --------------------------BEGIN INCLUDED TEXT-------------------- Cisco NX-OS Software Authenticated Simple Network Management Protocol Denial of Service Vulnerability Priority: High Advisory ID: cisco-sa-20181017-nxos-snmp FirstÂ Published: 2018Â OctoberÂ 17Â 16:00Â GMT VersionÂ 1.0: Final Workarounds: No workarounds available Cisco Bug IDs: CSCvj70029 CVE-2018-0456 CWE-20 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) input packet processor of Cisco NX-OS Software could allow an authenticated, remote attacker to cause the SNMP application of an affected device to restart unexpectedly. The vulnerability is due to improper validation of SNMP protocol data units (PDUs) in SNMP packets. An attacker could exploit this vulnerability by sending a crafted SNMP packet to an 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-20181017-nxos-snmp Affected Products o Vulnerable Products This vulnerability affects the following Cisco products if they are running a vulnerable release of Cisco NX-OS Software: Nexus 3000 Series Switches Nexus 3600 Platform Switches Nexus 9000 Series Switches in standalone NX-OS mode Nexus 9500 R-Series Line Cards and Fabric Modules The only vulnerable software release for Nexus 3000 Series Switches and for Nexus 9000 Series Switches in standalone NX-OS mode is 7.0(3)I7(3). The only vulnerable software release for Nexus 3600 Platform Switches and Nexus 9500 R-Series Line Cards and Fabric Modules is 7.0(3)F3(4). Refer to the Fixed Software section of this security advisory for more information about affected releases. Determining the Status of SNMP 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 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 the following Cisco products: Firepower 2100 Series Firepower 4100 Series Next-Generation Firewall Firepower 9300 Security Appliance MDS 9000 Series Multilayer Switches Nexus 1000V Switch for Microsoft Hyper-V Nexus 1000V Switch for VMware vSphere Nexus 2000 Series Switches Nexus 3500 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 Unified Computing System (UCS) 6100 Series Fabric Interconnects UCS 6200 Series Fabric Interconnects UCS 6300 Series Fabric Interconnects UCS 6400 Series Fabric Interconnects Details o 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 via IPv4 or IPv6. Only traffic directed to the affected system can be used to exploit this vulnerability. To exploit this vulnerability 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 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 via SNMP Version 3, the attacker must have user credentials for the affected system. Workarounds o There are no workarounds that address this vulnerability. As a mitigation for the vulnerability that is described in this advisory, administrators can configure an access control list (ACL) on an SNMP community. This ACL will 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 SNMP requests only from the trusted hosts 192.168.1.2 and 192.168.1.3: 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 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 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. Fixed Releases In the following tables, the left column lists releases of Cisco NX-OS Software. The right 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. Nexus 3000 Series Switches and 9000 Series Switches in Standalone NX-OS Mode: CSCvj70029 Cisco NX-OS Software Release First Fixed Release for This Vulnerability Prior to 7.0(3)I5 Not vulnerable 7.0(3)I5 Not vulnerable 7.0(3)I6 Not vulnerable 7.0(3)I7 7.0(3)I7(4) 9.2(1) Not vulnerable Nexus 3600 Platform Switches and 9500 R-Series Line Cards and Fabric Modules: CSCvj70029 Cisco NX-OS Software Release First Fixed Release for This Vulnerability 7.0(3) Software Maintenance Upgrades (SMUs) 7.0(3)F3(4) 9.2(1) Not vulnerable 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 during internal security 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. Subscribe to Cisco Security Notifications o Subscribe URL o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20181017-nxos-snmp Revision History o +----------+---------------------------+----------+--------+------------------+ | Version | Description | Section | Status | Date | +----------+---------------------------+----------+--------+------------------+ | 1.0 | Initial public release. | - | Final | 2018-October-17 | +----------+---------------------------+----------+--------+------------------+ - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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