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AUSCERT External Security Bulletin Redistribution
ESB-2020.3297
Cisco IOS XE Software Zone-Based Firewall Denial of Service Vulnerabilities
25 September 2020
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco IOS XE Software Zone-Based Firewall
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
CVE Names: CVE-2020-3480 CVE-2020-3421
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-94ckG4G
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Cisco IOS XE Software Zone-Based Firewall Denial of Service Vulnerabilities
Priority: High
Advisory ID: cisco-sa-zbfw-94ckG4G
First Published: 2020 September 24 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds availableCisco Bug IDs: CSCvs71952CSCvt52986
CVE-2020-3421
CVE-2020-3480
CWE-754
Summary
o Multiple vulnerabilities in the Zone-Based Firewall feature of Cisco IOS XE
Software could allow an unauthenticated, remote attacker to cause the
device to reload or stop forwarding traffic through the firewall.
The vulnerabilities are due to incomplete handling of Layer 4 packets
through the device. An attacker could exploit these vulnerabilities by
sending a certain sequence of traffic patterns through the device. A
successful exploit could allow the attacker to cause the device to reload
or stop forwarding traffic through the firewall, resulting in a denial of
service.
For more information about these vulnerabilities, see the Details section
of this advisory.
Cisco has released software updates that address these vulnerabilities.
There are no workarounds that address these vulnerabilities.
This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-zbfw-94ckG4G
This advisory is part of the September 24, 2020, release of the Cisco IOS
and IOS XE Software Security Advisory Bundled Publication, which includes
25 Cisco Security Advisories that describe 34 vulnerabilities. For a
complete list of the advisories and links to them, see Cisco Event
Response: September 2020 Semiannual Cisco IOS and IOS XE Software Security
Advisory Bundled Publication .
Affected Products
o Vulnerable Products
These vulnerabilities affect devices that are running a vulnerable release
of Cisco IOS XE Software and have the Zone-Based Firewall feature enabled
with Layer 4 inspection enabled. The vulnerabilities are independent of
each other.
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Determine the Device Configuration
CVE-2020-3421
The device is affected if the log dropped-packets feature is configured
under the inspection parameter map. Administrators can validate this by
logging into the device and using the show run | section parameter-map
command. If the output contains any line with log dropped-packets , the
device is vulnerable. The following examples show variations on a
vulnerable configuration where the log dropped-packets feature is enabled
either on the global inspect policy or on a custom-named inspect policy (if
any of these appear in the configuration, the device is vulnerable):
router_zbfw#show running-config | section parameter-map
parameter-map type inspect cisco-sa-zbfw-94ckG4G
log dropped-packets
router_zbfw#
router_zbfw#show running-config | section parameter-map
parameter-map type inspect-global
log dropped-packets
router_zbfw#
router_zbfw#show running-config | section parameter-map
parameter-map type inspect global
log dropped-packets
router_zbfw#
CVE-2020-3480
The device is affected if the one-minute high feature is configured under
the inspection parameter map. Administrators can validate this by logging
into the device and using the show run | section parameter-map command. If
the output contains any line with one-minute high , the device is
vulnerable. The following example shows variations on a vulnerable
configuration where the one-minute high feature is enabled:
router_zbfw#show running-config | section parameter-map
parameter-map type inspect cisco-sa-zbfw-94ckG4G
one-minute low 400
one-minute high 500
router_zbfw#
Products Confirmed Not Vulnerable
Only products listed in the Vulnerable Products section of this advisory
are known to be affected by these vulnerabilities.
Cisco has confirmed that these vulnerabilities do not affect the following
Cisco products:
IOS Software
IOS XR Software
NX-OS Software
Details
o The vulnerabilities are not dependent on one another. Exploitation of one
of the vulnerabilities is not required to exploit the other vulnerability.
In addition, a software release that is affected by one of the
vulnerabilities may not be affected by the other vulnerability.
Details about the vulnerabilities are as follows:
CVE-2020-3421: Cisco IOS XE Software Zone-Based Firewall Denial of Service
Vulnerability
A vulnerability in the Zone-Based Firewall feature of Cisco IOS XE Software
could allow an unauthenticated, remote attacker to cause the device to
reload.
The vulnerability is due to incomplete handling of Layer 4 packets through
the device. An attacker could exploit this vulnerability by sending a
certain sequence of traffic patterns through the device. A successful
exploit could allow the attacker to cause the device to reload, resulting
in a denial of service.
Cisco has released software updates that address this vulnerability. There
are no workarounds that address this vulnerability.
Bug ID(s): CSCvs71952
CVE ID: CVE-2020-3421
Security Impact Rating (SIR): High
CVSS Base Score: 8.6
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
CVE-2020-3480: Cisco IOS XE Software Zone-Based Firewall Denial of Service
Vulnerability
A vulnerability in the Zone-Based Firewall feature of Cisco IOS XE Software
could allow an unauthenticated, remote attacker to cause the device to stop
forwarding traffic through the firewall.
The vulnerability is due to incomplete handling of Layer 4 packets through
the device. An attacker could exploit this vulnerability by sending a
certain sequence of traffic patterns through the device. A successful
exploit could allow the attacker to cause the device to stop forwarding
traffic through the firewall, resulting in a denial of service.
Cisco has released software updates that address this vulnerability. There
are no workarounds that address this vulnerability.
Bug ID(s): CSCvt52986
CVE ID: CVE-2020-3480
Security Impact Rating (SIR): High
CVSS Base Score: 8.6
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X
Workarounds
o There are no workarounds that address these vulnerabilities.
For administrators that observe CVE-2020-3421, removing the log
dropped-packets configuration until an upgrade can be performed is a viable
mitigation.
Fixed Software
o 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: 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.
Cisco IOS and IOS XE Software
To help customers determine their exposure to vulnerabilities in Cisco IOS
and IOS XE Software, Cisco provides the Cisco Software Checker to identify
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 the Cisco Software Checker to search advisories in the
following ways:
Choose the software and one or more releases
Upload a .txt file that includes a list of specific releases
Enter the output of the show version command
After initiating a search, customers can customize the search to include
all Cisco Security Advisories, a specific advisory, or all advisories in
the most recent bundled publication.
Customers can also use the following form to determine whether a release is
affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE
Software release-for example, 15.1(4)M2 or 3.13.8S :
[ ] [Check]
By default, the Cisco Software Checker includes results only for
vulnerabilities that have a Critical or High Security Impact Rating (SIR).
To include results for Medium SIR vulnerabilities, customers can use the
Cisco Software Checker on Cisco.com and check the Medium check box in the
drop-down list under Impact Rating when customizing a search.
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.
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 vulnerabilities that is
described in this advisory.
Source
o These vulnerabilities were 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.
Related to This Advisory
o Cisco Event Response: September 2020 Semiannual Cisco IOS and IOS XE
Software Security Advisory Bundled Publication
URL
o https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-zbfw-94ckG4G
Revision History
o +----------+---------------------------+----------+--------+--------------+
| Version | Description | Section | Status | Date |
+----------+---------------------------+----------+--------+--------------+
| 1.0 | Initial public release. | - | Final | 2020-SEP-24 |
+----------+---------------------------+----------+--------+--------------+
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