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AUSCERT External Security Bulletin Redistribution
ESB-2020.2702.2
Cisco IOS XR Software Additional Paths Denial of Service Vulnerability
11 August 2020
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS XR Software
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote with User Interaction
Resolution: Patch/Upgrade
CVE Names: CVE-2020-3449
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-bgp-ErKEqAer
Revision History: August 11 2020: Update to v1.1 of advisory
August 6 2020: Initial Release
- --------------------------BEGIN INCLUDED TEXT--------------------
Cisco IOS XR Software Additional Paths Denial of Service Vulnerability
Priority: Medium
Advisory ID: cisco-sa-bgp-ErKEqAer
First Published: 2020 August 5 16:00 GMT
Last Updated: 2020 August 10 13:37 GMT
Version 1.1: Final
Workarounds: No workarounds availableCisco Bug IDs: CSCvu54677
CVE-2020-3449
CWE-754
Summary
o A vulnerability in the Border Gateway Protocol (BGP) additional paths
feature of Cisco IOS XR Software could allow an unauthenticated, remote
attacker to prevent authorized users from monitoring the BGP status and
cause the BGP process to stop processing new updates, resulting in a denial
of service (DOS) condition.
The vulnerability is due to an incorrect calculation of lexicographical
order when displaying additional path information within Cisco IOS XR
Software, which causes an infinite loop. An attacker could exploit this
vulnerability by sending a specific BGP update from a BGP neighbor peer
session of an affected device; an authorized user must then issue a show
bgp command for the vulnerability to be exploited. A successful exploit
could allow the attacker to prevent authorized users from properly
monitoring the BGP status and prevent BGP from processing new updates,
resulting in outdated information in the routing and forwarding tables.
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-bgp-ErKEqAer
Affected Products
o Vulnerable Products
At the time of publication, this vulnerability affected Cisco IOS XR
Software releases earlier than 7.1.2, 7.2.1, and 7.3.1.
See the Details section in the bug ID(s) at the top of this advisory for
the most complete and current information.
To be vulnerable, the device needs to be configured to receive additional
paths under any of the supported address families.
Determine the Device Configuration
To determine whether the device is configured to receive additional paths,
check the output of the show running-config router bgp | include
additional-paths receive command. The following example shows the output of
the show running-config router bgp | include additional-paths receive
command for a device that is vulnerable:
RP/0/RSP1/CPU0:9904#show run router bgp | include additional-paths receive
Wed Aug 5 10:38:42.316 UTC
additional-paths receive
RP/0/RSP1/CPU0:9904#
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by this vulnerability.
Details
o The information in the BGP update that causes this vulnerability is locally
generated by the BGP neighbor peer session of the affected device. Cisco
IOS Software, Cisco IOS XR Software, and Cisco NX-OS Software would never
generate a BGP update that would result in the show bgp commands
incorrectly calculating the lexicographical order when displaying
additional path information. The BGP update would need to come from a BGP
implementation other than one done by a Cisco network operating system.
For a device to be affected by this vulnerability, both of the following
conditions must be met:
The BGP update that causes this vulnerability is processed by the
device and the data is inserted into the BGP table.
An authorized user executes show bgp commands that incorrectly
calculate lexicographical order when displaying additional path
information.
Once show bgp commands are executed (as long as the offending data is in
the BGP table), the affected device will return an error message that is
similar to the following example:
% Failed to retrieve data from EDM server: 'sysdb' detected the 'warning' condition 'An
EDM took too long to process a request and was timed out'
Once the device is affected, further BGP updates will not be processed.
While there is no immediate data plane loss, if there is network churn,
information in future BGP updates will fail to update the BGP table and
result in outdated routing and forwarding tables.
Workarounds
o There are no workarounds that address this vulnerability.
Once the device is in the state that is caused by the vulnerability,
restarting the BGP process will allow the device to continue to process BGP
correctly. However, any additional show bgp commands will return the device
to the vulnerable state.
Fixed Software
o When considering software upgrades , customers are advised to regularly
consult the advisories for Cisco products, which are available from the
Cisco Security Advisories 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.
Fixed Releases
At the time of publication, Cisco IOS XR Software releases 7.1.2, 7.2.1,
and 7.3.1 contained the fix for this vulnerability.
At the time of publication, the SMUs in the following table were available.
Customers who require SMUs for other platforms and releases are advised to
contact their support organization.
IOS XR Release Platform SMU ID
6.5.3 ASR9K AA17486
See the Details section in the bug ID(s) at the top of this advisory for
the most complete and current information.
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 the resolution of a Cisco TAC support
case.
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.
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-bgp-ErKEqAer
Revision History
o +---------+--------------------------+-------------+--------+-------------+
| Version | Description | Section | Status | Date |
+---------+--------------------------+-------------+--------+-------------+
| | Changed the first fixed | Vulnerable | | |
| 1.1 | release in the 7.1 train | Products, | Final | 2020-AUG-05 |
| | to 7.1.2 instead of | Fixed | | |
| | 7.1.3. | Software | | |
+---------+--------------------------+-------------+--------+-------------+
| 1.0 | Initial public release. | - | Final | 2020-AUG-05 |
+---------+--------------------------+-------------+--------+-------------+
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