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Fencer Intel
medium 5.8

CVE-2026-20221 json

Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities

published 19d ago modified 18d ago also EUVD-2026-107378

cvss
5.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.6%
EPSS 0.6% chance of exploitation in 30 days, percentile 47%
public exploits
0
none known

Summary

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.

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
18d ago

Exploit prediction

0.58% chance of exploitation in the next 30 days, higher than 47% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 5.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

Affected products

  • 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

Classification

Weakness

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.