CVE-2020-3565

Cisco Firepower Threat Defense Software TCP Intercept Bypass Vulnerability

MEDIUM
5.8
CVSS Score
Published: October 21, 2020 at 06:40 PM UTC
Updated: August 11, 2026 at 07:37 PM UTC
1 product affected across 1 vendorSecure Firewall Threat Defense

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Severity
MEDIUM5.8
Exploit prediction
EPSS 0.9%
SSVC
No known exploit

Description

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 6.4.0.86.5.0 ≤ v < 6.5.0.46.5.0.5 ≤ v < 6.6.0

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.8MEDIUMcisco
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
CHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-284CWE-287

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