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AUSCERT External Security Bulletin Redistribution
Multiple Cisco Products Snort Ethernet Frame Decoder Denial
of Service Vulnerability
4 March 2021
AusCERT Security Bulletin Summary
Product: Cisco Products
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2021-1285
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Multiple Cisco Products Snort Ethernet Frame Decoder Denial of Service
Advisory ID: cisco-sa-snort-ethernet-dos-HGXgJH8n
First Published: 2021 March 3 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvu88170
CVE Names: CVE-2021-1285
o Multiple Cisco products are affected by a vulnerability in the Ethernet
Frame Decoder of the Snort detection engine that could allow an
unauthenticated, adjacent attacker to cause a denial of service (DoS)
The vulnerability is due to improper handling of error conditions when
processing Ethernet frames. An attacker could exploit this vulnerability by
sending malicious Ethernet frames through an affected device. A successful
exploit could allow the attacker to exhaust disk space on the affected
device, which could result in administrators being unable to log in to the
device or the device being unable to boot up correctly.
Note: Manual intervention is required to recover from this situation.
Customers are advised to contact the Cisco Technical Assistance Center
(TAC) to help recover a device in this 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:
o Vulnerable Products
This vulnerability affects all open source Snort project releases earlier
than Release 2.9.17. For more information on open source Snort, see the
Snort website .
Impact to Cisco Products
This vulnerability affects the following Cisco products, if they are
running a vulnerable release of Cisco UTD Snort IPS Engine Software for IOS
XE or Cisco UTD Engine for IOS XE SD-WAN Software and are configured to
pass Ethernet frames to the Snort detection engine:
1000 Series Integrated Services Routers (ISRs)
4000 Series Integrated Services Routers (ISRs)
Catalyst 8000V Edge Software
Catalyst 8200 Series Edge Platforms
Catalyst 8300 Series Edge Platforms
Cloud Services Router 1000V Series
Integrated Services Virtual Router (ISRv)
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory.
Products Confirmed Not Vulnerable
Cisco has confirmed that this vulnerability does not affect the following
3000 Series Industrial Security Appliances (ISAs)
Adaptive Security Appliance (ASA) Software
Catalyst 8500 Series Edge Platforms
Catalyst 8500L Series Edge Platforms
Firepower Management Center (FMC) Software
Firepower Threat Defense (FTD) Software ^ 1
Meraki Security Appliances
1. A related vulnerability affecting Cisco FTD Software was previously
resolved and disclosed as Cisco Firepower Threat Defense Software Inline
Pair/Passive Mode Denial of Service Vulnerability .
o There are no workarounds that address this vulnerability.
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
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 page , to determine exposure and a complete
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
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
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
Customers are advised to upgrade to an appropriate fixed software release
as indicated in the following table(s):
Cisco IOS XE Software and Cisco IOS XE SD-WAN Software
Cisco UTD Snort IPS Engine Software for First Fixed Release for This
IOS XE and Vulnerability
Cisco UTD Engine for IOS XE SD-WAN
Earlier than 16.12 Migrate to a fixed release.
17.1 Migrate to a fixed release.
17.2 Migrate to a fixed release.
1. Starting with release 17.2.1, Cisco IOS XE Software and Cisco IOS XE
SD-WAN Software share the same image file.
Open Source Snort
The open source Snort project versions 2.9.17 and later contain the fix for
this vulnerability. For more information on open source Snort, see the
Snort website .
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.
o This vulnerability was found during the resolution of a Cisco TAC support
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.
| Version | Description | Section | Status | Date |
| 1.0 | Initial public release. | - | Final | 2021-MAR-03 |
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