CVE-2026-20221
Reported by cisco · Published October 21, 2026
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.
Risk scores
Affected products
| Vendor | Product | Versions |
|---|---|---|
| Cisco | Cisco Cyber Vision | 3.0.0, 3.0.2, 3.0.3 |
| Cisco | Cisco Open Source Snort3 | 3.12.2.0, 3.1.2.0, 3.1.3.0 |
| Cisco | Cisco Secure Firewall Threat Defense (FTD) Software | 7.0.0, 7.0.0.1, 7.0.1 |
| Cisco | Cisco Umbrella Insights Virtual Appliance | 2.6.0, 2.5.6, 2.5 |
| Cisco | Cisco UTD SNORT IPS Engine Software | 3.17.1S, 16.12.3, Fuji-16.9.5 |
| Cisco | Cisco Secure Firewall Threat Defense (FTD) Software | 7.0.0, 7.0.0.1, 7.0.1 |
| Cisco | Cisco Open Source Snort3 | 3.1.72.0, 3.1.73.0, 3.1.74.0 |
| Cisco | Cisco Cyber Vision | 5.0.0, 3.0.0, 3.0.2 |
| Cisco | Cisco UTD SNORT IPS Engine Software | 17.9.10, 16.12.6, 17.6.2 |
| Cisco | Cisco Umbrella Insights Virtual Appliance | 2.5.6, 2.5, 2.4.12 |
Timeline
- Oct 21, 2026 CVE Published
- Oct 22, 2026 EPSS Score (4 in total, the first dated here)
- Oct 22, 2026 Coalition ESS Score
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The same record, from the CLI:
vulnetix vdb vuln CVE-2026-20221
vulnetix vdb fixes CVE-2026-20221Or with curl, using the org id and key from your account page:
curl -s -H "Authorization: ApiKey ${VULNETIX_ORG_ID}:${VULNETIX_API_KEY}" \
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