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No exploitation reportedFix available

CVE-2021-1402

No exploitation reported by the sources we read.

  • Published2021-04-29
  • Fixed in6.6.0 · 6.4.0
  • WeaknessCWE-119 · CWE-20

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC
  1. 2021-04-2918:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-1402?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-1402?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Cisco secure firewall threat defenseversion to verify
BranchAffectedFixed in
6.x≥ 6.5.0, < 6.6.06.6.0
6.x≥ 6.3.0, < 6.4.06.4.0

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Cisco secure firewall threat defense to 6.6.0 · 6.4.0

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub

Sources

  • CISA-ADPSSVC decisionnone2024-11-08
  • OpenCVESSVC decisionnone—
  • NVDCVSS 3.18.6read 2026-10-23
  • CNACVSS 3.08.6read 2026-10-23
  • NVDCVSS 2.07.8read 2026-10-23
  • CNAweakness (CWE)CWE-119read 2026-10-23
  • NVDweakness (CWE)CWE-20read 2026-10-23
  • FIRST EPSSEPSS score1.4 %2026-10-23

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Published
2021-04-29
Last Modified
2026-08-11
NVD status
Modified

Frequently asked questions

What is CVE-2021-1402?

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.

Is CVE-2021-1402 actively exploited?

Active exploitation of CVE-2021-1402 has not been confirmed. Its EPSS score was 1.4% on 2026-10-23, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-1402?

CVE-2021-1402 has a CVSS v3 base score of 8.6 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H.

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