CVE-2026-20221
Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities
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.
Weakness: CWE-476
Affected products
| Vendor | Product | Category | Matched by |
|---|---|---|---|
| Cisco | Cisco Cyber Vision | OT / IoT Security | cna-assigner |
| Cisco | Cisco Firepower Threat Defense (FTD) Check your version | Firewall / NGFW | cna-assigner |
| Cisco | Cisco UTD SNORT IPS Engine | Threat Detection & Sandbox | cna-assigner |
| Cisco | Cisco Umbrella | SASE / SSE / Secure Web | cna-assigner |
Vendor-reported products (5)
- Cisco · Cisco Cyber Vision
- Cisco · Cisco Open Source Snort3
- Cisco · Cisco Secure Firewall Threat Defense (FTD) Software
- Cisco · Cisco Umbrella Insights Virtual Appliance
- Cisco · Cisco UTD SNORT IPS Engine Software
Vendor advisory
Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerability
Cisco’s rating: Medium (advisory CVSS 5.8) · Published Oct 21, 2026
Bug IDs: CSCwt66239 , CSCwt83029 , CSCwt83034 , CSCwu04383
The vendor’s rating applies to the whole advisory and can differ from this CVE’s own CVSS severity. Where this comes from