Medium 5.8Published Oct 21, 2026

CVE-2026-20221Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities

Updated under an hour ago (Oct 27, 2026, 5:10 PM ET)

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It affects Cisco Cyber Vision and 4 other products. Add what you run to find out whether that includes you.

No exploitation reported and no EPSS estimate yet.

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Every CVE for Cisco Cyber Vision

Exploited in the last 30 days

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.

CVSS: 5.8 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L
Weakness (CWE): CWE-476
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: cisco
NVD analysis: Awaiting Analysis
Record last updated: Oct 22, 2026
First seen by InfoSec Signals: Oct 21, 2026

Affected products

Affected products

Cisco Cisco Cyber Vision cisco:cyber_vision (from the name)	3.0.0; 3.0.2; 3.0.3; 3.0.1; 3.1.0; 3.0.4; 3.1.1; 3.1.2; and 53 more ranges	CNA record
Cisco Cisco Open Source Snort3 cisco:open_source_snort3 (from the name)	3.12.2.0; 3.1.2.0; 3.1.3.0; 3.1.4.0; 3.1.5.0; 3.1.6.0; 3.1.7.0; 3.1.8.0; and 97 more ranges	CNA record
Cisco Cisco Secure Firewall Threat Defense (FTD) Software cisco:secure_firewall_threat_defense_ftd_software (from the name)	7.0.0; 7.0.0.1; 7.0.1; 7.0.1.1; 7.0.2; 7.2.0; 7.0.2.1; 7.0.3; and 52 more ranges	CNA record
Cisco Cisco Umbrella Insights Virtual Appliance cisco:umbrella_insights_virtual_appliance (from the name)	2.6.0; 2.5.6; 2.5; 2.4.12; 2.7; 2.6.2; 2.5.5; 2.5.4; and 65 more ranges	CNA record
Cisco Cisco UTD SNORT IPS Engine Software cisco:utd_snort_ips_engine_software (from the name)	3.17.1S; 16.12.3; Fuji-16.9.5; 16.12.4; 17.3.1a; 16.6.6; 16.12.2; Fuji-16.9.6; and 108 more ranges	CNA record

References

References

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort3-gre-JNpMHrTv

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.