CVE-2021-1236: Multiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker...

Description

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.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Probability

2.15%

79.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Cisco	Ios Xe	< 17.4.1
Cisco	Firepower Threat Defense	< 6.5.0.5
Cisco	Secure Firewall Management Center	2.9.14.0
Cisco	Secure Firewall Management Center	2.9.14.14
Cisco	Secure Firewall Management Center	2.9.15
Cisco	Secure Firewall Management Center	2.9.16
Cisco	Secure Firewall Management Center	2.9.17
Snort	Snort	< 2.9.14

References

Timeline

Published: Jan 13, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-1236?

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.

How severe is CVE-2021-1236?

CVE-2021-1236 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 2.15% probability of exploitation in the next 30 days.

How do I fix CVE-2021-1236?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.