CVE-2021-34781

What it is

A vulnerability in the processing of SSH connections for multi-instance deployments of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on the affected device. This vulnerability is due to a lack of proper error handling when an SSH session fails to be established. An attacker could exploit this vulnerability by sending a high rate of crafted SSH connections to the instance. A successful exploit could allow the attacker to cause resource exhaustion, which causes a DoS condition on the affected device. The device must be manually reloaded to recover.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

1.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-10-27 19:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-08-11 19:33 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.4% in the next 30 days (EPSS).
• Severity: 8.6 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-10-27 19:15 UTC

Last modified

2026-08-11 19:33 UTC

Exploit probability

1.4% · EPSS, next 30 days

Weakness

CWE-119 · Buffer errors

Record status

Modified

Affected

• Cisco Firepower Management Center Virtual Appliance 6.3.0
• Cisco Firepower Management Center Virtual Appliance 6.4.0
• Cisco Firepower Management Center Virtual Appliance 6.4.0.13
• Cisco Firepower Management Center Virtual Appliance 6.5.0
• Cisco Firepower Management Center Virtual Appliance 6.6.0
• Cisco Firepower Management Center Virtual Appliance 6.7.0.3
• Cisco Firepower Management Center Virtual Appliance 6.7.1
• Cisco Firepower Management Center Virtual Appliance 7.0.0

Attack profile CVSS 3.1 · 8.6

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

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