CVE-2021-40116: Cisco Secure Firewall Management Center

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

Multiple Cisco products are affected by a vulnerability in Snort rules that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.The vulnerability is due to improper handling of the Block with Reset or Interactive Block with Reset actions if a rule is configured without proper constraints. An attacker could exploit this vulnerability by sending a crafted IP packet to the affected device. A successful exploit could allow the attacker to cause through traffic to be dropped. Note: Only products with Snort3 configured and either a rule with Block with Reset or Interactive Block with Reset actions configured are vulnerable. Products configured with Snort2 are not vulnerable.

Affected products

• Cisco Secure Firewall Management Center: version 3.1.0.1 only
• Cisco Secure Firewall Threat Defense: from 6.4.0, before 6.4.0.13 (fixed in 6.4.0.13); from 6.6.0, before 6.6.5.1 (fixed in 6.6.5.1); 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 Snort: from 3.0.0.0, before 3.1.0.100 (fixed in 3.1.0.100)

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