CVE-2026-20221

Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities

MEDIUM

5.8

CVSS Score

Published: October 21, 2026 at 04:12 PM UTC

Updated: October 22, 2026 at 07:11 PM UTC

5 products affected across 1 vendorSecure Firewall Threat DefenseUnified Threat Defense Snort Intrusion Prevention System EngineCisco Cyber Vision

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Severity

MEDIUM5.8

Exploit prediction

EPSS 0.6%

SSVC

No known exploit

Description

Multiple Cisco products are affected by a vulnerability in the generic routing encapsulation (GRE) tunnel decapsulation feature of the Snort 3 Detection Engine that could allow an unauthenticated, remote attacker to cause an unexpected restart of the Snort 3 Detection Engine. This vulnerability is due to improper handling of nested GRE traffic. An attacker could exploit this vulnerability by sending a crafted GRE payload through an affected device. A successful exploit could allow the attacker to trigger an unexpected reload of the Snort 3 Detection Engine, resulting in either a bypass or denial of service (DoS) condition, depending on device configuration. For more information, see the section of this advisory. The Snort 3 Detection Engine will restart automatically. No manual intervention is required.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Cisco Open Source Snort3 · Cisco

90%

3.1.10.03.1.12.03.1.13.03.1.14.03.1.15.03.1.16.03.1.17.03.1.18.03.1.19.03.1.2.03.1.20.03.1.21.03.1.22.03.1.23.03.1.24.03.1.25.03.1.27.03.1.28.03.1.29.03.1.3.03.1.30.03.1.31.03.1.32.03.1.36.03.1.38.03.1.39.03.1.4.03.1.40.03.1.41.03.1.42.03.1.43.03.1.45.03.1.47.03.1.48.03.1.5.03.1.50.03.1.51.03.1.52.03.1.53.03.1.55.03.1.56.03.1.57.03.1.58.03.1.59.03.1.6.03.1.60.03.1.61.03.1.62.03.1.63.03.1.64.03.1.65.03.1.66.03.1.67.03.1.69.03.1.7.03.1.70.03.1.71.03.1.72.03.1.73.03.1.74.03.1.75.03.1.76.03.1.77.03.1.78.03.1.8.03.1.81.03.1.82.03.1.83.03.1.84.03.1.9.03.10.0.03.10.1.03.10.2.03.11.1.03.12.1.03.12.2.03.2.1.03.2.2.03.3.0.03.3.1.03.3.2.03.3.3.03.3.4.03.3.5.03.3.7.03.5.0.03.5.1.03.5.2.03.6.0.03.6.1.03.6.2.03.6.3.03.7.0.03.7.1.03.7.2.03.7.3.03.7.4.03.8.1.03.9.0.03.9.1.03.9.2.03.9.3.03.9.5.03.9.6.03.9.7.0

Cisco Cyber Vision · Cisco

90%