Cisco Security Advisory
Cisco Firepower Threat Defense Software TCP Intercept Bypass Vulnerability
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CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N/E:X/RL:X/RC:X
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A vulnerability in the TCP Intercept functionality of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass configured Access Control Policies (including Geolocation) and Service Polices on an affected system.
The vulnerability exists because TCP Intercept is invoked when the embryonic connection limit is reached, which can cause the underlying detection engine to process the packet incorrectly. An attacker could exploit this vulnerability by sending a crafted stream of traffic that matches a policy on which TCP Intercept is configured. A successful exploit could allow the attacker to match on an incorrect policy, which could allow the traffic to be forwarded when it should be dropped. In addition, the traffic could incorrectly be dropped.
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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-tcp-intercept-bypass-xG9M3PbY
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Vulnerable Products
At the time of publication, this vulnerability affected Cisco FTD Software releases earlier than 6.4.0.8, 6.5.0.4, and 6.6.0 if TCP Intercept is configured.
See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
Determine Whether TCP Intercept is Configured
In the Cisco Firepower Management Center (FMC) GUI, choose Access Control > Access Control > Threat Defense Policy (for the rule) and check if there is a value configured for Connections > Maximum Embryonic and Connections Per Client > Maximum Embryonic.
For additional information, see Threat Defense Service Policies.
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 Cisco Adaptive Security Appliance (ASA) Software or Cisco Firepower Management Center (FMC) Software.
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By default, there are no limits on how many connections can go to or through a Cisco FTD device. To protect servers from denial of service (DoS) attacks, administrators can use policy rules to set limits on particular traffic classes. Specifically, setting limits on embryonic connections (those that have not finished the TCP handshake), will protect against SYN flooding attacks. When embryonic connection limits are exceeded, the TCP Intercept component gets involved to proxy connections and ensure that attacks are throttled.
For additional information, see Protect Servers from a SYN Flood DoS Attack (TCP Intercept).
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There are no workarounds that address this vulnerability.
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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 FTD Software releases 6.4.0.8 and later, 6.5.0.4 and later, and 6.6.0 and later contained the fix for this vulnerability.
See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.
To upgrade to a fixed release of Cisco FTD Software, do one of the following:
- For devices that are managed by using Cisco Firepower Management Center (FMC), use the FMC interface to install the upgrade. After installation is complete, reapply the access control policy.
- For devices that are managed by using Cisco Firepower Device Manager (FDM), use the FDM interface to install the upgrade. After installation is complete, reapply the access control policy.
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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.
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This vulnerability was found during the resolution of a Cisco TAC support case.
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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.
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Show LessVersion Description Section Status Date 1.0 Initial public release. - Final 2020-OCT-21
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