CVE-2021-1236: Cisco IOS XE

Medium severity, CVSS 5.3. EPSS: 2.2% chance of exploitation in the next 30 days.

Multiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker to bypass the configured policies on an affected system. The vulnerability is due to a flaw in the detection algorithm. An attacker could exploit this vulnerability by sending crafted packets that would flow through an affected system. A successful exploit could allow the attacker to bypass the configured policies and deliver a malicious payload to the protected network.

Affected products

• Cisco IOS XE: before 17.4.1 (fixed in 17.4.1)
• Cisco Secure Firewall Management Center: version 2.9.14.0 only; version 2.9.14.14 only; version 2.9.15 only; version 2.9.16 only; version 2.9.17 only
• Cisco Secure Firewall Threat Defense: before 6.5.0.5 (fixed in 6.5.0.5)
• Snort Snort: before 2.9.14 (fixed in 2.9.14)

Published 2021-01-13. Last modified 2026-08-11.