Summary

• Multiple Cisco products are affected by a vulnerability involving the Open Shortest Path First (OSPF) Routing Protocol Link State Advertisement (LSA) database. This vulnerability could allow an unauthenticated, remote attacker to take full control of the OSPF Autonomous System (AS) domain routing table, allowing the attacker to intercept or black-hole traffic.
  
  The attacker could exploit this vulnerability by injecting crafted OSPF packets. Successful exploitation could cause the targeted router to flush its routing table and propagate the crafted OSPF LSA type 1 update throughout the OSPF AS domain.
  
  To exploit this vulnerability, an attacker must accurately determine certain parameters within the LSA database on the target router. This vulnerability can only be triggered by sending crafted unicast or multicast OSPF LSA type 1 packets. No other LSA type packets can trigger this vulnerability.
  
  The Fabric Shortest Path First (FSPF) protocol is not affected by this vulnerability.
  
  Workarounds that address this vulnerability are available.
  
  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170727-ospf

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products with an OSPF implementation. Refer to the Fixed Software section for information on fixed software.
  
  Note: This vulnerability can be triggered only by targeting the OSPF multicast address or directly targeting OSPF-enabled interfaces.
  
  FSPF is not affected by this vulnerability.
  

  Cisco IOS and Cisco IOS XE Software

  Cisco devices that are running Cisco IOS or Cisco IOS XE Software and configured for OSPF are vulnerable. Devices that do not have OSPF enabled are not affected by this vulnerability.
  
  OSPFv3 is not affected by this vulnerability.
  
  To determine if a Cisco IOS or Cisco IOS XE device is configured with OSPF on an interface, use the show ip ospf interface command. The following example is the output of the show ip ospf interface command on a Cisco IOS device configured with OSPF and enabled on the GigabitEthernet0/0/1 interface:
  
  

  Router# show ip ospf interface 
  GigabitEthernet0/0/1 is up, line protocol is up
  Internet Address 192.168.2.4/24, Area 0, Attached via Network Statement
  Process ID 1, Router ID 10.10.10.4, Network Type BROADCAST, Cost: 1
  Topology-MTID    Cost    Disabled    Shutdown      Topology Name
        0           1         no          no            Base
  Transmit Delay is 1 sec, State DR, Priority 1
  .
  .
  .

  
  To determine the Cisco IOS or Cisco IOS XE Software release that is running on a Cisco product, administrators can log into the device and issue the show version command to display the system banner. The system banner confirms that the device is running Cisco IOS Software by displaying text similar to Cisco Internetwork Operating System Software or Cisco IOS Software. The image name displays in parentheses, followed by Version and the Cisco IOS Software release name. Other Cisco devices do not have the show version command or may provide different output.
  
  The following example identifies a Cisco product that is running Cisco IOS Software Release 15.0(1)M1 with an installed image name of C3900-UNIVERSALK9-M:

  Router# show version
  Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.0(1)M1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2009 by cisco Systems, Inc.
  Compiled Wed 02-Dec-09 17:17 by prod_rel_team
  .
  .
  .

  Additional information about Cisco IOS Software release naming conventions is available in White Paper: Cisco IOS and NX-OS Software Reference Guide.
  
  

  Cisco Adaptive Security Appliance

  Cisco devices that are running Cisco Adaptive Security Appliance (ASA) Software and configured for OSPF are vulnerable. Devices that do not have OSPF enabled are not affected by this vulnerability.
  
  OSPFv3 is not affected by this vulnerability.
  
  To determine if a Cisco ASA device is configured with OSPF on an interface, use the show ospf interface brief command. The following example is the output of the show ospf interface brief command on a Cisco ASA device configured with OSPF and enabled on the inside interface:
  

  ciscoasa# show ospf interface brief
  Interface    PID   Area   IP Address/Mask         Cost  State Nbrs F/C
  inside       1     1      10.10.10.1/255.255.255.0  10    WAIT 0/0
  ciscoasa#

  To determine the version of software that is running on a Cisco ASA, Cisco ASA-SM, or Cisco Pix security appliances, use the show version command from the CLI. The following is an example of the output from the show version command:
  

  ciscoasa# show version | include Software
  Cisco Adaptive Security Appliance Software Version 9.3(1)
  ciscoasa#

  Cisco NX-OS Software

  Cisco devices that are running Cisco NX-OS Software and configured for OSPF are vulnerable. Devices that do not have OSPF enabled are not affected by this vulnerability. To determine if a Cisco NX-OS device is configured with OSPF on an interface, use the show ip ospf interface command similar to the example provided in the Cisco IOS and Cisco IOS XE Software section.
  
  To determine the version of Cisco NX-OS Software that is running on Cisco Nexus 3000, 5000, 6000, 7000 and 9000 series devices, use the show version command from the CLI. The following is an example of the output from the show version command:
  

  switch# show version | grep system:
    system:    version 7.3(1)D1(1)
  switch#

  
  Exploiting the vulnerability on a Cisco Nexus device will not affect the local routing table of a Cisco Nexus device. However, the Cisco Nexus device will install and propagate the crafted LSA to other devices in the OSPF area. Crafted LSA propagated to other routers that are part of the same OSPF AS may affect the routing tables across the OSPF AS.

  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 the following Cisco products:
  

  • Cisco IOS XR Software
  • Cisco StarOS Software
  • Cisco Connected Grid Routers
  • Cisco Nexus 1000v Series

Details

• OSPF is a routing protocol defined by RFC 2328. It is designed to manage IP routing inside an AS. OSPF packets use IP protocol number 89.
  
  Affected network devices running the OSPF protocol may be impacted by this vulnerability if they receive a crafted LSA type 1 packet. This packet does not have to be acknowledged, and it can originate from a spoofed IP address.
  
  In order to exploit this vulnerability, an attacker needs to determine a number of factors, such as the network placement and IP address of the target router, LSA DB sequence numbers, and the router ID of the OSPF Designated Router (DR). An attacker needs to know all of the factors in order to exploit this vulnerability.
  
  Because OSPF processes unicast packets as well as multicast packets, this vulnerability can be exploited remotely and can be used to target multiple systems on the local segment simultaneously. Using OSPF authentication as described in the Workarounds section can mitigate the effects of this vulnerability. Using OSPF authentication is a highly recommended security best practice, regardless of the presence of this vulnerability.
  
  Once processed, a crafted LSA type 1 packet may cause a targeted router to flush the content of its routing table and propagate the crafted LSA update throughout the OSPF area. OSPF member routers of the same area would be affected by processing and installing a crafted LSA type 1 packet propagated by the victim router. This may lead to a number of consequences, such as false routes injected into the OSPF routing table, traffic sent to a black hole, or traffic redirected to a destination that is controlled by an attacker.
  
  In order to recover affected systems, administrators can delete the OSPF configuration from the affected device and enable it again. Alternatively, a reload is required to recover affected systems. Clearing the OSPF process or routing table by means of commands such as clear ip ospf process or clear ip route does not have any effect and cannot be used to recover affected systems.

Indicators of Compromise

• Exploitation of this vulnerability will cause the targeted router to have inconsistent information in its Router Link States LSA database, where the Link ID information will not match Advertising Router ID in the product equivalent output of the show ip ospf database command. This vulnerability affects only Router LSAs (LSA type 1).
  
  The following is the output of the show ip ospf database command in Cisco IOS, Cisco IOS XE, and Cisco NX-OS devices affected by this vulnerability:

  Router# show ip ospf database
      OSPF Router with ID (10.10.10.1) (Process ID 1)
      Router Link States (Area 0)
      Link ID         ADV Router      Age    Seq#  Checksum Link count
      10.10.10.4      10.10.10.4      334    0x8000000E 0x00E29A 3
      10.10.10.1      192.168.27.11   22     0x80000011 0x0062A8 3
      10.10.10.2      10.10.10.2      298    0x80000018 0x00394A 2
      10.10.10.3      10.10.10.3      305    0x80000020 0x00E715 3 

  
  The following is the output of the show ospf database command in a Cisco ASA device affected by this vulnerability:
  

  ciscoasa# show ospf database
      OSPF Router with ID (192.168.1.2) (Process ID 1)
      Router Link States (Area 0)
      Link ID         ADV Router      Age    Seq#  Checksum Link count
      10.10.10.4      10.10.10.4      334    0x8000000E 0x00E29A 3
      10.10.10.1      192.168.27.11   22     0x80000011 0x0062A8 3
      10.10.10.2      10.10.10.2      298    0x80000018 0x00394A 2
      10.10.10.3      10.10.10.3      305    0x80000020 0x00E715 3
      .
      .
      .

  
  Note: An affected targeted router will propagate the crafted LSA throughout the OSPF area. If the vulnerability is successfully exploited, all the routers in the same OSPF area will have a copy of the crafted LSA type 1 entry in the OSPF LSA database.

Workarounds

• There are workarounds that address this vulnerability. The use of OSPF authentication should be used as a best practice and as a mitigation. OSPF packets without a valid key will not be processed. MD5 authentication is highly recommended, due to inherent weaknesses in plaintext authentication. With plain text authentication, the authentication key will be sent unencrypted over the network, which can allow an attacker on a local network segment to capture the key by sniffing packets.

  Refer to http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a0080094069.shtml for more information about OSPF authentication.

Fixed Software

• Cisco has released free software updates that address the vulnerabilities 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:
  http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.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: http://www.cisco.com/en/US/support/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 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 menu 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 3.1.4S—in the following field:
  
  

  
  For a mapping of Cisco IOS XE Software releases to Cisco IOS Software releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE Software release.
  
  

  Cisco ASA, Cisco FTD, and Cisco NX-OS Software

  For information about fixed software releases, consult the Cisco bug ID(s) at the top of this advisory.

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 and reported to Cisco by Dr. Gabi Nakibly from Rafael Advanced Defense Systems.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170727-ospf

Revision History

• Version	Description	Section	Status	Date
  2.0	Updated vulnerable product information to include Nexus 9000 devices, Nexus 3000 devices, and NX-OS Software configured with OSPFv3.	Affected Products	Final	2017-August-03
  1.1	Added links to the Cisco IOS Software Checker.	Fixed Software	Final	2017-July-28
  1.0	Initial public release.	—	Final	2017-July-27

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