Cisco Security Advisory
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CVSS:3.0/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:X/RL:X/RC:X
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A vulnerability in the VLAN Trunking Protocol (VTP) subsystem of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to corrupt the internal VTP database on an affected device and cause a denial of service (DoS) condition.
The vulnerability is due to a logic error in how the affected software handles a subset of VTP packets. An attacker could exploit this vulnerability by sending VTP packets in a sequence that triggers a timeout in the VTP message processing code of the affected software. A successful exploit could allow the attacker to impact the ability to create, modify, or delete VLANs and cause a DoS condition.
There are workarounds that address this vulnerability.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180926-vtp
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Vulnerable Products
This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS Software or Cisco IOS XE Software, are operating in VTP client mode or VTP server mode, and do not have a VTP domain name configured.
The default configuration for Cisco devices that are running Cisco IOS Software or Cisco IOS XE Software and support VTP is to operate in VTP server mode with no domain name configured.
For information about which Cisco IOS and IOS XE Software releases are vulnerable, see the Fixed Software section of this advisory.
Determining the VTP Configuration
To determine the VTP operating mode and whether a VTP domain name has been configured for a device, administrators can log in to the device, use the show vtp status command in the CLI, and refer to the output of the command.
The following example shows the output of the show vtp status command for a device that is using the default configuration, which is to operate in VTP server mode with no VTP domain name configured. If the device is also running a vulnerable release of Cisco IOS Software or Cisco IOS XE Software, the device is affected by this vulnerability.
Switch# show vtp status VTP Version capable : 1 to 3 VTP version running : 1 VTP Domain Name : VTP Pruning Mode : Disabled VTP Traps Generation : Disabled Device ID : 0cd9.9675.dd80 Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00 Local updater ID is 192.168.88.1 on interface Vl1 (lowest numbered VLAN interface found) Feature VLAN: -------------- VTP Operating Mode : Server Maximum VLANs supported locally : 1005 Number of existing VLANs : 5 Configuration Revision : 0 MD5 digest : 0x57 0xCD 0x40 0x65 0x63 0x59 0x47 0xBD 0x56 0x9D 0x4A 0x3E 0xA5 0x69 0x35 0xBC Switch#The following example shows the output of the show vtp status command for a device that is operating in VTP server mode and has the VTP domain name MYVTPDOMAIN. The device is not affected by this vulnerability because a VTP domain name has been configured for the device.
Switch# show vtp status VTP Version capable : 1 to 3 VTP version running : 1 VTP Domain Name : MYVTPDOMAIN VTP Pruning Mode : Disabled VTP Traps Generation : Disabled Device ID : 0cd9.9675.dd80 Configuration last modified by 0.0.0.0 at 0-0-00 00:00:00 Local updater ID is 192.168.88.1 on interface Vl1 (lowest numbered VLAN interface found) Feature VLAN: -------------- VTP Operating Mode : Server Maximum VLANs supported locally : 1005 Number of existing VLANs : 5 Configuration Revision : 0 MD5 digest : 0xFE 0x33 0x43 0x04 0x9D 0x91 0x37 0x58 0x66 0xA0 0x68 0x3F 0x74 0x6A 0x22 0x5B Switch#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.
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 Software, Cisco IOS XE Software, or similar text.
The following example shows the output of the command for a device that is running Cisco IOS XE Software Release 16.2.1 and has an installed image name of CAT3K_CAA-UNIVERSALK9-M:
ios-xe-device# show version Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M), Version Denali 16.2.1, RELEASE SOFTWARE (fc1) Technical Support: http://www.cisco.com/techsupport Copyright (c) 1986-2016 by Cisco Systems, Inc. Compiled Sun 27-Mar-16 21:47 by mcpre . . .For information about the naming and numbering conventions for Cisco IOS XE Software releases, see the Cisco IOS and NX-OS Software Reference Guide.
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 IOS XR Software or Cisco NX-OS Software.
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This vulnerability is due to a logic error in how the affected software handles a subset of VTP packets. An attacker could exploit this vulnerability by sending VTP packets in a sequence that triggers a timeout in the VTP message processing code of the affected software.
For exploitation of this vulnerability to occur, a device must receive the VTP packets through a port that is operating as a trunk port. A device will not process the VTP packets if they are received on a port that is operating as an access port.
On most Cisco devices that are running Cisco IOS Software or Cisco IOS XE Software and support VTP, the default port configuration for a switch port is dynamic auto. A port in the dynamic auto configuration can be converted to a trunk port by a device that is connected to it. Administrators who are using this configuration on their switch ports should determine whether such behavior is required or desirable. If it is not and the ports are expected to be used only to provide network access to hosts, administrators may consider reconfiguring their switch ports to be static access ports.
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Exploitation of this vulnerability could generate the following logging messages:
Aug 29 2018 13:02:57.434 EST: %SW_VLAN-4-VTP_INTERNAL_ERROR: VLAN manager received an internal error 4 from vtp function vtp_get_domain_info: No such domain -Traceback= 463F74z 1DE5DE4z 2253E40z 2257D14z 2254C88z 22593C8z 2B0A128z 2B0A194z 225AA28z 225827Cz 2255540z 297DD08z 297A088z Aug 29 2018 13:03:27.445 EST: %SW_VLAN-4-VTP_INTERNAL_ERROR: VLAN manager received an internal error 4 from vtp function vtp_get_domain_info: No such domain -Traceback= 463F74z 1DE5DE4z 2253E40z 2257D14z 2254C88z 22593C8z 2B0A128z 2B0A194z 225AA28z 225827Cz 2255540z 297DD08z 297A088z Aug 29 2018 13:03:57.444 EST: %SW_VLAN-4-VTP_INTERNAL_ERROR: VLAN manager received an internal error 4 from vtp function vtp_get_domain_info: No such domain -Traceback= 463F74z 1DE5DE4z 2253E40z 2257D14z 2254C88z 22593C8z 2B0A128z 2B0A194z 225AA28z 225827Cz 2255540z 297DD08z 297A088z Aug 29 2018 13:04:27.449 EST: %SW_VLAN-4-VTP_INTERNAL_ERROR: VLAN manager received an internal error 4 from vtp function vtp_get_domain_info: No such domain -Traceback= 463F74z 1DE5DE4z 2253E40z 2257D14z 2254C88z 22593C8z 2B0A128z 2B0A194z 225AA28z 225827Cz 2255540z 297DD08z 297A088zThe messages will occur approximately every 30 seconds. The values printed after the -Traceback= text are version dependent.
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For detailed information about affected and fixed software releases, consult the Cisco IOS Software Checker.
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.
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 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 or Cisco IOS XE Software release—for example, 15.1(4)M2 or 3.13.8S—in the following field:
By default, the Cisco IOS Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, use the Cisco IOS Software Checker on Cisco.com and check the Medium check box in the Impact Rating drop-down list.
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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.
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Cisco would like to thank Mr. Marcin T. Sleczek of networkers.pl for reporting this vulnerability.
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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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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2018-September-26
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