{"cve":"CVE-2020-3421","nvd":{"published":"2020-09-24T18:15:18.917","modified":"2026-06-17T03:18:14.340","status":"Modified","description":"Multiple vulnerabilities in the Zone-Based Firewall feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause the device to reload or stop forwarding traffic through the firewall. The vulnerabilities are due to incomplete handling of Layer 4 packets through the device. An attacker could exploit these vulnerabilities by sending a certain sequence of traffic patterns through the device. A successful exploit could allow the attacker to cause the device to reload or stop forwarding traffic through the firewall, resulting in a denial of service. For more information about these vulnerabilities, see the Details section of this advisory.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-754"],"references":["https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-94ckG4G","https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-94ckG4G"],"products":["cisco:ios_xe"],"source":"nvd","synced_at":"2026-10-19T21:09:53.489947993+00:00"},"epss":{"cve":"CVE-2020-3421","score":0.0193,"percentile":0.80004,"date":"2026-10-31"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}