{"schema_version":"public-product-v1.1","generated_at":"2026-07-21T11:05:10Z","exposure_verdict":"not_assessed","verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure.","advisory":{"id":"cisco-sa-zbfw-tguGuYq","slug":"cisco-sa-zbfw-tguguyq","vendor":"Cisco","title":"Cisco IOS XE Software Protection Against Distributed Denial of Service Attacks Feature Vulnerability","summary":"A vulnerability in the Protection Against Distributed Denial of Service Attacks feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to conduct denial of service (DoS) attacks to or through the affected device. This vulnerability is due to incorrect programming of the half-opened connections limit, TCP SYN flood limit, or TCP SYN cookie features when the features are configured in vulnerable releases of Cisco IOS XE Software. An attacker could exploit this vulnerability by attempting to flood traffic to or through the affected device. A successful exploit could allow the attacker to initiate a DoS attack to or through an affected device. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link:https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq This advisory is part of the September 2021 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.","severity":"Medium","published_at":"2021-09-22T16:00:00Z","updated_at":"2021-09-22T16:00:00Z","source_url":"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq","csaf_url":"https://sec.cloudapps.cisco.com/security/center/contentjson/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq/csaf/cisco-sa-zbfw-tguGuYq.json","exposure_verdict":"not_assessed","verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure."},"freshness":{"last_source_refreshed_at":"2026-07-21T05:16:34Z","latest_source_refresh_at":"2026-07-21T05:16:34Z","oldest_source_refresh_at":"2026-07-21T03:00:03Z","all_sources_fresh":true,"sources":[{"source":"cisco_advisories","label":"Cisco advisories","last_success_at":"2026-07-21T03:00:03Z","stale":false},{"source":"cisco_csaf","label":"Cisco CSAF","last_success_at":"2026-07-21T05:14:24Z","stale":false},{"source":"nvd_cves","label":"NVD CVEs","last_success_at":"2026-07-21T05:16:30Z","stale":false},{"source":"cisa_kev","label":"CISA KEV","last_success_at":"2026-07-21T05:16:31Z","stale":false},{"source":"first_epss","label":"EPSS","last_success_at":"2026-07-21T05:16:34Z","stale":false}]},"summary":{"cve_count":1,"visible_product_count":2,"public_evidence_count":2,"kev_count":0,"highest_epss":0.01328},"cves":[{"id":"CVE-2021-34697","kev":false,"epss":{"score":0.01328,"percentile":0.67872,"score_date":"2026-07-20","updated_at":"2026-07-21T05:16:34Z"}}],"public_evidence":[{"product":{"name":"Cisco IOS XE Software","slug":"cisco-ios-xe-software","vendor":"Cisco"},"cve":{"id":"CVE-2021-34697"},"evidence_type":"structured_affected","evidence_label":{"scope":"CSAF product evidence","label":"product_status known affected"},"evidence_source":"Cisco CSAF","source":"Cisco CSAF","source_document_fetched_at":"2026-07-20T00:55:18Z","csaf_status":"known_affected","csaf_product_status":"known_affected","csaf_product_status_path":"vulnerabilities[].product_status.known_affected","raw_product_name":"17.11.99SW; 17.2.1; 17.2.1a; 17.2.1r; 17.2.1v; 17.2.2; 17.2.3; 17.3.1; 17.3.1a; 17.3.1w; 17.3.1x; 17.3.1z; 17.3.2; 17.3.2a; 17.4.1; 17.4.1a; 17.4.1b; 17.4.1c","exposure_verdict":"not_assessed","verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure.","exposure_verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure.","kev":false,"epss":{"score":0.01328,"score_date":"2026-07-20","updated_at":"2026-07-21T05:16:34Z"},"published_at":"2021-09-22T16:00:00Z","updated_at":"2021-09-22T16:00:00Z","advisory_updated_at":"2021-09-22T16:00:00Z","source_url":"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq","remediation":{"url":"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq"},"row_display_order":1},{"product":{"name":"Cisco IOS XE Catalyst SD-WAN","slug":"cisco-ios-xe-catalyst-sd-wan","vendor":"Cisco"},"cve":{"id":"CVE-2021-34697"},"evidence_type":"structured_affected","evidence_label":{"scope":"CSAF product evidence","label":"product_status known affected"},"evidence_source":"Cisco CSAF","source":"Cisco CSAF","source_document_fetched_at":"2026-07-20T00:55:18Z","csaf_status":"known_affected","csaf_product_status":"known_affected","csaf_product_status_path":"vulnerabilities[].product_status.known_affected","raw_product_name":"Cisco IOS XE Catalyst SD-WAN","exposure_verdict":"not_assessed","verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure.","exposure_verdict_reason":"Public evidence does not evaluate exact release, platform, enabled features, configuration, compensating controls, or live exposure.","kev":false,"epss":{"score":0.01328,"score_date":"2026-07-20","updated_at":"2026-07-21T05:16:34Z"},"published_at":"2021-09-22T16:00:00Z","updated_at":"2021-09-22T16:00:00Z","advisory_updated_at":"2021-09-22T16:00:00Z","source_url":"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq","remediation":{"url":"https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-tguGuYq"},"row_display_order":2}]}