Cisco Firepower Threat Defense Software SSL Decryption Policy Denial of Service Vulnerability

published 2021-04-29 5 y ago modified 2026-08-11 2 mo ago also EUVD-2021-6869

cvss: 8.6; version 3.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 1.4%; EPSS 1.4% chance of exploitation in 30 days, percentile 72%
public exploits: 0; none known

A vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message through an affected device. SSL/TLS messages sent to an affected device do not trigger this vulnerability. A successful exploit could allow the attacker to cause a process to crash. This crash would then trigger a reload of the device. No manual intervention is needed to recover the device after the reload.

Patch / fix

fixed in 1

cisco secure_firewall_threat_defense 6.4.0, 6.6.0

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 2 y ago (2024-11-08)

Exploit prediction

1.40% chance of exploitation in the next 30 days, higher than 72% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.0	8.6	CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
NVD	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
NVD	2.0	7.8	AV:N/AC:L/Au:N/C:N/I:N/A:C

Affected products

Cisco Cisco Firepower Threat Defense Software

Classification

Weakness

CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer
CWE-20 Improper Input Validation

References

tools.cisco.com /security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssl-decrypt-dos-DdyLuK6c
vendor-advisory

Sources

CVE List CVE-2021-1402
NVD CVE-2021-1402

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Summary