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TI-2026-78819 Aliases CVE-2026-20221GHSA-vm6m-qmxg-cg2c

Cisco Snort 3 nested GRE flaw lets attackers restart detection engine

Priority LOW 33CWE-476Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · Low
Fix status
No fix listed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA. Impact type from CWE-476.

Summary

Cisco Cyber Vision, Cisco Open Source Snort3, Cisco Secure Firewall Threat Defense (FTD) Software, Cisco Umbrella Insights Virtual Appliance and Cisco UTD SNORT IPS Engine Software are affected. Improper handling of nested GRE traffic in Snort 3 causes a NULL pointer dereference (CWE-476). An unauthenticated remote attacker can make the Snort 3 Detection Engine restart by sending crafted GRE traffic through an affected device, causing a bypass or denial of service depending on configuration.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Description from the CNA

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00577 47th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
CiscoCisco Cyber Vision3.0.0; 3.0.2; 3.0.3; 3.0.1; 3.1.0; 3.0.4; 3.1.1; 3.1.2; 3.2.0; 3.0.5; 3.2.1; 3.0.6; 3.2.2; 3.2.3; 3.2.4; 4.0.0; 4.0.1; 4.0.2; 4.0.3; 4.1.0; 4.1.1; 4.1.2; 4.1.3; 4.1.4; 4.2.0; 4.2.1; 4.1.5; 4.2.2; 4.2.X; 4.2.3; 4.2.4; 4.2.6; 4.1.6; 4.3.0; 4.3.1; 4.3.2; 4.3.3; 4.4.0; 4.4.1; 4.4.2; 4.4.3; 4.1.7; 5.0.0; 5.0.1; 5.0.2; 5.1.0; 5.1.1; 5.1.2; 5.1.3; 5.2.0; 5.2.1; 5.3.0; 5.3.1; 5.3.2; 5.3.3; 5.5.1; 5.6.1; 5.6.0; 5.4.0; 5.4.1; 5.4.2—No fix listedCNA
CiscoCisco Open Source Snort33.12.2.0; 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; 3.1.9.0; 3.1.10.0; 3.1.12.0; 3.1.13.0; 3.1.14.0; 3.1.15.0; 3.1.16.0; 3.1.17.0; 3.1.18.0; 3.1.19.0; 3.1.20.0; 3.1.21.0; 3.1.22.0; 3.1.23.0; 3.1.24.0; 3.1.25.0; 3.1.27.0; 3.1.28.0; 3.1.29.0; 3.1.30.0; 3.1.31.0; 3.1.32.0; 3.1.36.0; 3.1.38.0; 3.1.39.0; 3.1.40.0; 3.1.41.0; 3.1.42.0; 3.1.43.0; 3.1.45.0; 3.1.47.0; 3.1.48.0; 3.1.50.0; 3.1.51.0; 3.1.52.0; 3.1.53.0; 3.1.55.0; 3.1.56.0; 3.1.57.0; 3.1.58.0; 3.1.59.0; 3.1.60.0; 3.1.61.0; 3.1.62.0; 3.1.63.0; 3.1.64.0; 3.1.65.0; 3.1.66.0; 3.1.67.0; 3.1.69.0; 3.1.70.0; 3.1.71.0; 3.1.72.0; 3.1.73.0; 3.1.74.0; 3.1.75.0; 3.1.76.0; 3.1.77.0; 3.1.78.0; 3.1.81.0; 3.1.82.0; 3.1.83.0; 3.1.84.0; 3.2.1.0; 3.2.2.0; 3.3.0.0; 3.3.1.0; 3.3.2.0; 3.3.3.0; 3.3.4.0; 3.3.5.0; 3.3.7.0; 3.5.0.0; 3.5.1.0; 3.8.1.0; 3.6.0.0; 3.6.2.0; 3.9.3.0; 3.7.2.0; 3.7.0.0; 3.9.6.0; 3.10.0.0; 3.10.2.0; 3.7.4.0; 3.9.0.0; 3.5.2.0; 3.12.1.0; 3.6.1.0; 3.9.2.0; 3.6.3.0; 3.9.5.0; 3.7.1.0; 3.9.7.0; 3.7.3.0; 3.10.1.0; 3.9.1.0; 3.11.1.0—No fix listedCNA
CiscoCisco Secure Firewall Threat Defense (FTD) Software7.0.0; 7.0.0.1; 7.0.1; 7.0.1.1; 7.0.2; 7.2.0; 7.0.2.1; 7.0.3; 7.2.0.1; 7.0.4; 7.2.1; 7.0.5; 7.3.0; 7.2.2; 7.2.3; 7.3.1; 7.2.4; 7.0.6; 7.2.5; 7.2.4.1; 7.3.1.1; 7.4.0; 7.0.6.1; 7.2.5.1; 7.4.1; 7.2.6; 7.0.6.2; 7.4.1.1; 7.2.7; 7.2.5.2; 7.3.1.2; 7.2.8; 7.6.0; 7.4.2; 7.2.8.1; 7.0.6.3; 7.4.2.1; 7.2.9; 7.0.7; 7.7.0; 7.4.2.2; 7.2.10; 7.6.1; 7.4.2.3; 7.0.8; 7.6.2; 7.7.10; 7.7.11; 7.0.8.1; 7.6.2.1; 7.7.10.1; 7.4.2.4; 7.2.10.2; 7.4.3; 7.6.4; 10.0.0; 7.4.4; 7.0.9; 7.2.11; 7.4.7—No fix listedCNA
CiscoCisco Umbrella Insights Virtual Appliance2.6.0; 2.5.6; 2.5; 2.4.12; 2.7; 2.6.2; 2.5.5; 2.5.4; 2.8; 2.6.1; 2.5.7; 1.5.4; 1.5.5; 1.5.6; 2.0.0; 2.0.2; 2.0.3; 2.1.0; 2.1.2; 2.1.4; 2.1.5; 2.2; 2.2.1; 2.3; 2.3.1; 2.4; 2.4.4; 2.4.6; 2.8.9; 3.0; 3.1; 3.2; 2.8.1; 2.8.2; 2.8.3; 2.8.4; 2.8.5; 3.0.1; 3.0.2; 3.0.4; 3.0.5; 3.1.1; 3.1.2; 3.1.3; 3.1.4; 3.2.1; 3.2.2; 3.2.3; 3.3; 3.3.1; 3.3.2; 3.3.3; 3.3.4; 3.4; 3.4.1; 3.4.2; 3.4.3; 3.4.4; 3.4.5; 3.4.6; 3.5; 2.7.1; 2.7.2; 2.7.6; 2.7.9; 2.7.10; 3.5.1; 3.5.2; 3.6.1; 3.6.2; 3.7; 3.7.1; 3.8.3—No fix listedCNA
CiscoCisco UTD SNORT IPS Engine Software3.17.1S; 16.12.3; Fuji-16.9.5; 16.12.4; 17.3.1a; 16.6.6; 16.12.2; Fuji-16.9.6; 3.17.0S; Fuji-16.9.3; Denali-16.3.7; Fuji-16.9.2; Fuji-16.9.4; Everest-16.6.4; Everest-16.6.3; 16.6.5; Denali-16.3.5; 17.2.1r; 17.1.1; Everest-16.6.2; 16.6.7a; Denali-16.3.4; 16.6.1; Denali-16.3.9; Denali-16.3.3; 16.12.1a; 17.3.2; 17.4.1a; 16.12.5; 17.5.1; Fuji-16.9.7; 16.6.9; 17.3.3; 17.5.1a; 17.3.4; 17.3.4a; 17.4.2; 17.4.1b; 17.6.1a; 16.6.10; 17.7.1a; 16.12.6; Fuji-16.9.8; 17.6.2; 17.8.1a; 16.12.7; 17.3.5; 17.6.3; 17.6.3a; 17.7.2; 17.9.1a; 17.6.4; 17.10.1a; 17.3.6; 16.12.8; 17.3.7; 17.9.2a; 17.6.5; 17.11.1a; 17.9.3a; 17.12.1a; 17.9.4; 17.6.6; 17.3.8; 17.3.8a; 17.6.6a; 17.9.4a; 17.12.2; 17.13.1a; 17.9.5a; 17.12.3; 17.6.7; 17.14.1a; 17.12.4; 17.12.3a; 17.15.1a; 17.6.8; 17.9.6; 17.6.8a; 17.16.1a; 17.9.5e; 17.12.4a; 17.15.2c; 17.9.5f; 17.12.4b; 17.15.2a; 17.12.5; 17.17.1; 17.12.5a; 17.9.7a; 17.15.3a; 17.15.3; 17.12.5b; 17.12.5c; 17.15.4; 17.9.7b; 17.18.1; 17.18.1a; 17.12.6; 17.9.8; 17.15.4c; 17.12.5d; 17.18.2; 26.1.1; 17.15.5; 17.15.5a; 17.12.7; 17.12.7a; 17.12.7b; 17.9.9; 17.18.3a; 17.12.8; 17.15.6; 17.18.4; 26.1.2; 17.9.10—No fix listedCNA
  • Cisco Cyber Vision VendorCisco Affected 3.0.0; 3.0.2; 3.0.3; 3.0.1; 3.1.0; 3.0.4; 3.1.1; 3.1.2; 3.2.0; 3.0.5; 3.2.1; 3.0.6; 3.2.2; 3.2.3; 3.2.4; 4.0.0; 4.0.1; 4.0.2; 4.0.3; 4.1.0; 4.1.1; 4.1.2; 4.1.3; 4.1.4; 4.2.0; 4.2.1; 4.1.5; 4.2.2; 4.2.X; 4.2.3; 4.2.4; 4.2.6; 4.1.6; 4.3.0; 4.3.1; 4.3.2; 4.3.3; 4.4.0; 4.4.1; 4.4.2; 4.4.3; 4.1.7; 5.0.0; 5.0.1; 5.0.2; 5.1.0; 5.1.1; 5.1.2; 5.1.3; 5.2.0; 5.2.1; 5.3.0; 5.3.1; 5.3.2; 5.3.3; 5.5.1; 5.6.1; 5.6.0; 5.4.0; 5.4.1; 5.4.2 Fixed in — No fix listed CNA
  • Cisco Open Source Snort3 VendorCisco Affected 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; 3.1.9.0; 3.1.10.0; 3.1.12.0; 3.1.13.0; 3.1.14.0; 3.1.15.0; 3.1.16.0; 3.1.17.0; 3.1.18.0; 3.1.19.0; 3.1.20.0; 3.1.21.0; 3.1.22.0; 3.1.23.0; 3.1.24.0; 3.1.25.0; 3.1.27.0; 3.1.28.0; 3.1.29.0; 3.1.30.0; 3.1.31.0; 3.1.32.0; 3.1.36.0; 3.1.38.0; 3.1.39.0; 3.1.40.0; 3.1.41.0; 3.1.42.0; 3.1.43.0; 3.1.45.0; 3.1.47.0; 3.1.48.0; 3.1.50.0; 3.1.51.0; 3.1.52.0; 3.1.53.0; 3.1.55.0; 3.1.56.0; 3.1.57.0; 3.1.58.0; 3.1.59.0; 3.1.60.0; 3.1.61.0; 3.1.62.0; 3.1.63.0; 3.1.64.0; 3.1.65.0; 3.1.66.0; 3.1.67.0; 3.1.69.0; 3.1.70.0; 3.1.71.0; 3.1.72.0; 3.1.73.0; 3.1.74.0; 3.1.75.0; 3.1.76.0; 3.1.77.0; 3.1.78.0; 3.1.81.0; 3.1.82.0; 3.1.83.0; 3.1.84.0; 3.2.1.0; 3.2.2.0; 3.3.0.0; 3.3.1.0; 3.3.2.0; 3.3.3.0; 3.3.4.0; 3.3.5.0; 3.3.7.0; 3.5.0.0; 3.5.1.0; 3.8.1.0; 3.6.0.0; 3.6.2.0; 3.9.3.0; 3.7.2.0; 3.7.0.0; 3.9.6.0; 3.10.0.0; 3.10.2.0; 3.7.4.0; 3.9.0.0; 3.5.2.0; 3.12.1.0; 3.6.1.0; 3.9.2.0; 3.6.3.0; 3.9.5.0; 3.7.1.0; 3.9.7.0; 3.7.3.0; 3.10.1.0; 3.9.1.0; 3.11.1.0 Fixed in — No fix listed CNA
  • Cisco Secure Firewall Threat Defense (FTD) Software VendorCisco Affected 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; 7.2.0.1; 7.0.4; 7.2.1; 7.0.5; 7.3.0; 7.2.2; 7.2.3; 7.3.1; 7.2.4; 7.0.6; 7.2.5; 7.2.4.1; 7.3.1.1; 7.4.0; 7.0.6.1; 7.2.5.1; 7.4.1; 7.2.6; 7.0.6.2; 7.4.1.1; 7.2.7; 7.2.5.2; 7.3.1.2; 7.2.8; 7.6.0; 7.4.2; 7.2.8.1; 7.0.6.3; 7.4.2.1; 7.2.9; 7.0.7; 7.7.0; 7.4.2.2; 7.2.10; 7.6.1; 7.4.2.3; 7.0.8; 7.6.2; 7.7.10; 7.7.11; 7.0.8.1; 7.6.2.1; 7.7.10.1; 7.4.2.4; 7.2.10.2; 7.4.3; 7.6.4; 10.0.0; 7.4.4; 7.0.9; 7.2.11; 7.4.7 Fixed in — No fix listed CNA
  • Cisco Umbrella Insights Virtual Appliance VendorCisco Affected 2.6.0; 2.5.6; 2.5; 2.4.12; 2.7; 2.6.2; 2.5.5; 2.5.4; 2.8; 2.6.1; 2.5.7; 1.5.4; 1.5.5; 1.5.6; 2.0.0; 2.0.2; 2.0.3; 2.1.0; 2.1.2; 2.1.4; 2.1.5; 2.2; 2.2.1; 2.3; 2.3.1; 2.4; 2.4.4; 2.4.6; 2.8.9; 3.0; 3.1; 3.2; 2.8.1; 2.8.2; 2.8.3; 2.8.4; 2.8.5; 3.0.1; 3.0.2; 3.0.4; 3.0.5; 3.1.1; 3.1.2; 3.1.3; 3.1.4; 3.2.1; 3.2.2; 3.2.3; 3.3; 3.3.1; 3.3.2; 3.3.3; 3.3.4; 3.4; 3.4.1; 3.4.2; 3.4.3; 3.4.4; 3.4.5; 3.4.6; 3.5; 2.7.1; 2.7.2; 2.7.6; 2.7.9; 2.7.10; 3.5.1; 3.5.2; 3.6.1; 3.6.2; 3.7; 3.7.1; 3.8.3 Fixed in — No fix listed CNA
  • Cisco UTD SNORT IPS Engine Software VendorCisco Affected 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; 3.17.0S; Fuji-16.9.3; Denali-16.3.7; Fuji-16.9.2; Fuji-16.9.4; Everest-16.6.4; Everest-16.6.3; 16.6.5; Denali-16.3.5; 17.2.1r; 17.1.1; Everest-16.6.2; 16.6.7a; Denali-16.3.4; 16.6.1; Denali-16.3.9; Denali-16.3.3; 16.12.1a; 17.3.2; 17.4.1a; 16.12.5; 17.5.1; Fuji-16.9.7; 16.6.9; 17.3.3; 17.5.1a; 17.3.4; 17.3.4a; 17.4.2; 17.4.1b; 17.6.1a; 16.6.10; 17.7.1a; 16.12.6; Fuji-16.9.8; 17.6.2; 17.8.1a; 16.12.7; 17.3.5; 17.6.3; 17.6.3a; 17.7.2; 17.9.1a; 17.6.4; 17.10.1a; 17.3.6; 16.12.8; 17.3.7; 17.9.2a; 17.6.5; 17.11.1a; 17.9.3a; 17.12.1a; 17.9.4; 17.6.6; 17.3.8; 17.3.8a; 17.6.6a; 17.9.4a; 17.12.2; 17.13.1a; 17.9.5a; 17.12.3; 17.6.7; 17.14.1a; 17.12.4; 17.12.3a; 17.15.1a; 17.6.8; 17.9.6; 17.6.8a; 17.16.1a; 17.9.5e; 17.12.4a; 17.15.2c; 17.9.5f; 17.12.4b; 17.15.2a; 17.12.5; 17.17.1; 17.12.5a; 17.9.7a; 17.15.3a; 17.15.3; 17.12.5b; 17.12.5c; 17.15.4; 17.9.7b; 17.18.1; 17.18.1a; 17.12.6; 17.9.8; 17.15.4c; 17.12.5d; 17.18.2; 26.1.1; 17.15.5; 17.15.5a; 17.12.7; 17.12.7a; 17.12.7b; 17.9.9; 17.18.3a; 17.12.8; 17.15.6; 17.18.4; 26.1.2; 17.9.10 Fixed in — No fix listed CNA

CPE names Threatist (inferred) · 2

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:cisco:cyber_vision_center:*:*:*:*:*:*:*:*——Cisco
cpe:2.3:a:cisco:secure_firewall_threat_defense:*:*:*:*:*:*:*:*——Cisco
  • cpe:2.3:a:cisco:cyber_vision_center:*:*:*:*:*:*:*:* Versions — — ·Cisco
  • cpe:2.3:a:cisco:secure_firewall_threat_defense:*:*:*:*:*:*:*:* Versions — — ·Cisco

Remediation

The sources list no fixed version for Cisco Cyber Vision, Cisco Open Source Snort3, Cisco Secure Firewall Threat Defense (FTD) Software, Cisco Umbrella Insights Virtual Appliance and Cisco UTD SNORT IPS Engine Software.

Written with Claude Haiku 5.5 from the sources below · 2026-10-28

Timeline

  1. 2026-10-21 Threatist record created from CVE-2026-20221
  2. 2026-10-21 Alias added: GHSA-vm6m-qmxg-cg2c
  3. 2026-10-22 CISA SSVC decision points changed
  4. 2026-10-22 Priority changed: MEDIUM → LOW

References

Other 1

  • TI-2026-74174 Arbitrary file write in Cisco Secure Email Gateway via AMP feature KEVCVSS 3.1CRITICAL 9.8
  • TI-2026-53490 Cisco Catalyst SD-WAN Manager System Account Authorization Bypass Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2026-53489 Cisco Secure Email Gateway SQL Injection Vulnerability KEVCVSS 3.1CRITICAL 9.8
  • TI-2026-53488 Cisco Identity Services Engine Authentication Bypass Vulnerability KEVCVSS 3.1CRITICAL 10.0
  • TI-2026-16388 Cisco Catalyst SD-WAN Controller Authentication Bypass Vulnerability KEVCVSS 3.1CRITICAL 10.0
  • TI-2026-16344 Cisco Secure Firewall Management Center Software Remote Code Execution Vulnerability KEVCVSS 3.1CRITICAL 10.0
See all 7059 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences