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CVE-2026-20221: Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities
- Severity: medium (CVSS 5.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.6% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-10-21 · updated 2026-10-22
- Weakness: CWE-476
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 products
- Cisco Open Source Snort3: 3.12.2.0, 3.1.2.0, 3.1.3.0, 3.1.4.0, 3.1.5.0, 3.1.6.0 (+99)
- Cisco Cyber Vision: 3.0.0, 3.0.2, 3.0.3, 3.0.1, 3.1.0, 3.0.4 (+55)
- Cisco Firepower Threat Defense Software: 7.0.0, 7.0.0.1, 7.0.1, 7.0.1.1, 7.0.2, 7.2.0 (+54)
- Cisco Umbrella Insights Virtual Appliance: 2.6.0, 2.5.6, 2.5, 2.4.12, 2.7, 2.6.2 (+67)
- Cisco UTD SNORT IPS Engine Software: 3.17.1S, 16.12.3, Fuji-16.9.5, 16.12.4, 17.3.1a, 16.6.6 (+110)
In the news
- Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerability
- Cisco Advance Notification for Publication of October 21, 2026, Security Advisories
References
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