CVE-2021-34781: Cisco Firepower Management Center Virtual Appliance

High severity, CVSS 7.5. EPSS: 1.4% chance of exploitation in the next 30 days.

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.

Affected products

• Cisco Firepower Management Center Virtual Appliance: version 6.3.0 only; version 6.4.0 only; version 6.4.0.13 only; version 6.5.0 only; version 6.6.0 only; version 6.7.0.3 only; …
• Cisco Secure Firewall Threat Defense: from 6.3.0, before 6.4.0.13 (fixed in 6.4.0.13); from 6.5.0, before 6.6.5 (fixed in 6.6.5); from 6.7.0, before 6.7.0.3 (fixed in 6.7.0.3); from 7.0.0, before 7.0.1 (fixed in 7.0.1)
• Cisco Sourcefire Defense Center: version 6.3.0 only; version 6.4.0 only; version 6.4.0.13 only; version 6.5.0 only; version 6.6.0 only; version 6.7.0.3 only; …

Published 2021-10-27. Last modified 2026-08-11.