CVE-2026-20067: Cisco Snort 3 detection engine denial of service

CVE-2026-20067 · Severity: medium · CVSS 5.8 · Published 2026-03-04

Cisco's Snort 3 detection engine, used in firewalls and security appliances to inspect network traffic, contains a vulnerability that allows remote attackers to crash the engine by sending specially crafted network packets. When the engine restarts unexpectedly, the firewall stops inspecting traffic, leaving the network unprotected until the service recovers.

Technologies: Cisco Catalyst 8000V Edge Software, Cisco Catalyst 8200 Series Edge Platforms, Cisco Catalyst 8300 Series Edge Platforms, Cisco Catalyst 8500L Edge Platforms, Cisco Cloud Services Router 1000V, Cisco Cyber Vision, Cisco IOS XE Software, Cisco Secure Firewall Threat Defense (FTD), Cisco Snort 3. Vendors: Cisco.

Quick answers

Is CVE-2026-20067 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-20067 being exploited in the wild.
How severe is CVE-2026-20067?
Medium severity, with a CVSS score of 5.8, published 4 March 2026.
Which products and versions are affected?
Cisco Catalyst 8000V Edge Software Multiple versions with UTD; Cisco Catalyst 8200 Series Edge Platforms Multiple versions with UTD; Cisco Catalyst 8300 Series Edge Platforms Multiple versions with UTD; Cisco Catalyst 8500L Edge Platforms Multiple versions with UTD; and 5 more.
Is there a fix for CVE-2026-20067?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-20067 attacked?
It is attacked over the network, in a network appliance.
Am I affected by CVE-2026-20067?
Check whether you run Cisco Catalyst 8000V Edge Software, Cisco Catalyst 8200 Series Edge Platforms, Cisco Catalyst 8300 Series Edge Platforms or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability exists in the Snort 3 detection engine's HTTP header parsing logic, specifically in the handling of Multicast DNS fields (CWE-248: Unchecked Error Condition). An unauthenticated remote attacker can exploit this by sending malformed HTTP packets over an established connection. The incomplete error checking fails to validate the DNS fields before processing, causing an unexpected restart of the detection engine and interrupting packet inspection. The attack requires network access but no authentication or user interaction. Patches are available from Cisco for affected software releases.

Affected products

  • Cisco Snort 3 Multiple versions
  • Cisco Secure Firewall Threat Defense (FTD) Multiple versions with Snort 3 configured
  • Cisco IOS XE Software Multiple versions with UTD Snort IPS Engine
  • Cisco Catalyst 8000V Edge Software Multiple versions with UTD
  • Cisco Catalyst 8200 Series Edge Platforms Multiple versions with UTD
  • Cisco Catalyst 8300 Series Edge Platforms Multiple versions with UTD
  • Cisco Catalyst 8500L Edge Platforms Multiple versions with UTD
  • Cisco Cloud Services Router 1000V Multiple versions with UTD
  • Cisco Cyber Vision Multiple versions

Timeline

  • 2026-03-04: disclosed: Cisco Security Advisory published

References

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