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AUSCERT External Security Bulletin Redistribution
Multiple Cisco Products Snort TCP Fast Open File Policy
14 January 2021
AusCERT Security Bulletin Summary
Product: Cisco Products
Publisher: Cisco Systems
Operating System: Cisco
Impact/Access: Reduced Security -- Remote/Unauthenticated
CVE Names: CVE-2021-1224
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Multiple Cisco Products Snort TCP Fast Open File Policy Bypass Vulnerability
Advisory ID: cisco-sa-snort-tfo-bypass-MmzZrtes
First Published: 2021 January 13 16:00 GMT
Version 1.0: Final
Workarounds: No workarounds available
Cisco Bug IDs: CSCvt43136 CSCvu88532
CVE Names: CVE-2021-1224
o Multiple Cisco products are affected by a vulnerability with TCP Fast Open
(TFO) when used in conjunction with the Snort detection engine that could
allow an unauthenticated, remote attacker to bypass a configured file
policy for HTTP.
The vulnerability is due to incorrect detection of the HTTP payload if it
is contained at least partially within the TFO connection handshake. An
attacker could exploit this vulnerability by sending crafted TFO packets
with an HTTP payload through an affected device. A successful exploit could
allow the attacker to bypass configured file policy for HTTP packets and
deliver a malicious payload.
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
At the time of publication, this vulnerability affected the following Cisco
products if they were running releases earlier than the first fixed release
of Cisco software:
1000 Series Integrated Services Routers (ISRs)
3000 Series Industrial Security Appliances (ISAs)
4000 Series Integrated Services Routers (ISRs)
Cloud Services Router 1000V
Firepower Threat Defense (FTD) Software
Integrated Services Virtual Router (ISRv)
For information about which Cisco software releases are vulnerable, see the
Fixed Software section of this advisory. See the Details section in the bug
ID(s) at the top of this advisory for the most complete and current
This vulnerability also affected all open source Snort project releases
earlier than Release 2.9.17. For more information, see the Snort website .
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 the following
Adaptive Security Appliance (ASA) Software
Firepower Management Center (FMC) Software
Meraki vMX100 Virtual Appliances
Meraki Z1 Appliances
Meraki Z3 Series Appliances
o There are no workarounds that address this vulnerability.
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
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
At the time of publication, Cisco Firepower Threat Defense (FTD) releases
6.7.0 and later contained the fix for this vulnerability when the Snort 2
option is configured.
At the time of publication, there were no fixes for Cisco FTD for this
vulnerability when the Snort 3 option is configured.
At the time of publication, Cisco UTD Snort IPS Engine Software for IOS XE
17.4.1 ^ 1 contained the fix for this vulnerability.
At the time of publication, Cisco had not released software updates that
address this vulnerability for Meraki MX Series Security Appliances.
At the time of publication, the open source Snort project release 2.9.17
and later contained the fix for this vulnerability. For more information,
see the Snort website .
At the time of publication, there were no fixes for open source Snort
project release 3.0. For more information, see the Snort website .
See the Details section in the bug ID(s) at the top of this advisory for
the most complete and current information.
1. Starting in 17.2.1, IOS XE and IOS XE SD-WAN use the same image file.
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 Cisco would like to thank Guillermo Munoz Mozos of BBVA for reporting this
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-JAN-13 |
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