CVE-2026-20104

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An attacker could exploit this vulnerability by manipulating the loaded binaries on an affected device to bypass some of the integrity checks that are performed during the boot process. A successful exploit could allow the attacker to execute code that bypasses the requirement to run Cisco-signed images.\r\n\r Cisco has assigned this security advisory a Security Impact Rating (SIR) of High rather than Medium as the score indicates because this vulnerability allows an attacker to bypass a major security feature of a device."}], "affected": [{"vendor": "Cisco", "product": "Cisco IOS XE Software", "versions": [{"version": "16.12.8", "status": "affected"}, {"version": "16.12.6", "status": "affected"}, {"version": "16.12.6a", "status": "affected"}, {"version": "16.12.7", "status": "affected"}, {"version": "17.3.3", "status": "affected"}, {"version": "17.3.4", "status": "affected"}, {"version": "17.3.5", "status": "affected"}, {"version": "17.3.6", "status": "affected"}, {"version": "17.3.4b", "status": "affected"}, {"version": "17.3.7", "status": "affected"}, {"version": "17.3.8", "status": "affected"}, {"version": "17.3.8a", "status": "affected"}, {"version": "17.4.1", "status": "affected"}, {"version": "17.5.1", "status": "affected"}, {"version": "17.6.1", "status": "affected"}, {"version": "17.6.2", "status": "affected"}, {"version": "17.6.3", "status": "affected"}, {"version": "17.6.1y", "status": "affected"}, {"version": "17.6.4", "status": "affected"}, {"version": "17.6.5", "status": "affected"}, {"version": "17.6.6", "status": "affected"}, {"version": "17.6.6a", "status": "affected"}, {"version": "17.6.5a", "status": "affected"}, {"version": "17.6.7", "status": "affected"}, {"version": "17.6.8", "status": "affected"}, {"version": "17.7.1", "status": "affected"}, {"version": "17.7.1a", "status": "affected"}, {"version": "17.10.1", "status": "affected"}, {"version": "17.8.1", "status": "affected"}, {"version": "17.8.1a", "status": "affected"}, {"version": "17.9.1", "status": "affected"}, {"version": "17.9.2", "status": "affected"}, {"version": "17.9.1a", "status": "affected"}, {"version": "17.9.3", "status": "affected"}, {"version": "17.9.4", "status": "affected"}, {"version": "17.9.5", "status": "affected"}, {"version": "17.9.4a", "status": "affected"}, {"version": "17.9.5b", "status": "affected"}, {"version": "17.9.6", "status": "affected"}, {"version": "17.9.6a", "status": "affected"}, {"version": "17.9.7", "status": "affected"}, {"version": "17.9.8", "status": "affected"}, {"version": "17.11.1", "status": "affected"}, {"version": "17.12.1", "status": "affected"}, {"version": "17.12.2", "status": "affected"}, {"version": "17.12.3", "status": "affected"}, {"version": "17.12.4", "status": "affected"}, {"version": "17.12.5", "status": "affected"}, {"version": "17.12.6", "status": "affected"}, {"version": "17.13.1", "status": "affected"}, {"version": "17.14.1", "status": "affected"}, {"version": "17.15.1", "status": "affected"}, {"version": "17.15.2", "status": "affected"}, {"version": "17.15.3", "status": "affected"}, {"version": "17.15.4", "status": "affected"}, {"version": "17.16.1", "status": "affected"}, {"version": "17.17.1", "status": "affected"}, {"version": "17.18.1", "status": "affected"}, {"version": "17.18.2", "status": "affected"}]}], "problemTypes": [{"descriptions": [{"lang": "en", "description": "Buffer Underwrite ('Buffer Underflow')", "type": "cwe", "cweId": "CWE-124"}]}], "references": [{"url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xe-secureboot-bypass-B6uYxYSZ", "name": "cisco-sa-xe-secureboot-bypass-B6uYxYSZ"}], "metrics": [{"format": "cvssV3_1", "cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N", "baseScore": 6.1, "baseSeverity": "MEDIUM", "attackVector": "PHYSICAL", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}}], "exploits": [{"lang": "en", "value": "The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory."}], "source": {"advisory": "cisco-sa-xe-secureboot-bypass-B6uYxYSZ", "discovery": "INTERNAL", "defects": ["CSCws75667", "CSCwr77016"]}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-03-26T17:39:46.810738Z", "id": "CVE-2026-20104", "options": [{"Exploitation": "none"}, {"Automatable": "no"}, {"Technical Impact": "total"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-03-26T17:39:54.940Z"}}]}}

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An attacker could exploit this vulnerability by manipulating the loaded binaries on an affected device to bypass some of the integrity checks that are performed during the boot process. 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"cpe:2.3:o:cisco:ios_xe:17.18.1:*:*:*:*:*:*:*", "matchCriteriaId": "1A57F16D-2020-46F1-BA1A-DAE484F31920", "vulnerable": true}, {"criteria": "cpe:2.3:o:cisco:ios_xe:17.18.2:*:*:*:*:*:*:*", "matchCriteriaId": "4E5872D0-4EB8-4B75-BD64-5E8E25B2D99E", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "A vulnerability in the bootloader of Cisco IOS XE Software for Cisco Catalyst 9200 Series Switches, Cisco Catalyst ESS9300 Embedded Series Switches, Cisco Catalyst IE9310 and IE9320 Rugged Series Switches, and Cisco IE3500 and IE3505 Rugged Series Switches could allow an authenticated, local attacker with level-15 privileges or an unauthenticated attacker with physical access to an affected device to execute arbitrary code at boot time and break the chain of trust.\r\n\r This vulnerability is due to insufficient validation of software at boot time. An attacker could exploit this vulnerability by manipulating the loaded binaries on an affected device to bypass some of the integrity checks that are performed during the boot process. A successful exploit could allow the attacker to execute code that bypasses the requirement to run Cisco-signed images.\r\n\r Cisco has assigned this security advisory a Security Impact Rating (SIR) of High rather than Medium as the score indicates because this vulnerability allows an attacker to bypass a major security feature of a device."}, {"lang": "es", "value": "Una vulnerabilidad en el bootloader del software Cisco IOS XE para los switches Cisco Catalyst serie 9200, los switches integrados Cisco Catalyst ESS9300, los switches robustos Cisco Catalyst IE9310 e IE9320, y los switches robustos Cisco IE3500 e IE3505 podr\u00eda permitir a un atacante local autenticado con privilegios de nivel 15 o a un atacante no autenticado con acceso f\u00edsico a un dispositivo afectado ejecutar c\u00f3digo arbitrario en el momento del arranque y romper la cadena de confianza.\nEsta vulnerabilidad se debe a una validaci\u00f3n insuficiente del software en el momento del arranque. Un atacante podr\u00eda explotar esta vulnerabilidad manipulando los binarios cargados en un dispositivo afectado para eludir algunas de las comprobaciones de integridad que se realizan durante el proceso de arranque. Un exploit exitoso podr\u00eda permitir al atacante ejecutar c\u00f3digo que elude el requisito de ejecutar im\u00e1genes firmadas por Cisco.\nCisco ha asignado a este aviso de seguridad una Calificaci\u00f3n de Impacto de Seguridad (SIR) de Alta en lugar de Media, como indica la puntuaci\u00f3n, porque esta vulnerabilidad permite a un atacante eludir una caracter\u00edstica de seguridad importante de un dispositivo."}], "id": "CVE-2026-20104", "lastModified": "2026-09-28T15:18:35.047", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "PHYSICAL", "availabilityImpact": "NONE", "baseScore": 6.1, "baseSeverity": "MEDIUM", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N", "version": "3.1"}, "exploitabilityScore": 0.9, "impactScore": 5.2, "source": "psirt@cisco.com", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-20104", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "total"}], "role": "CISA Coordinator", "timestamp": "2026-03-26T17:39:46.810738Z", "version": "2.0.3"}}]}, "published": "2026-03-25T16:16:14.143", "references": [{"source": "psirt@cisco.com", "tags": ["Vendor Advisory"], "url": "https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-xe-secureboot-bypass-B6uYxYSZ"}], "sourceIdentifier": "psirt@cisco.com", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-124"}], "source": "psirt@cisco.com", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "16.12.8"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "16.12.6"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "16.12.6a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "16.12.7"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.3.3"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.3.4"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.3.5"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.3.6"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.3.4b"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.3.7"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.3.8"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.3.8a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.4.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.5.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.2"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.3"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.6.1y"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.4"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.5"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.6"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.6.6a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.6.5a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.7"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.6.8"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.7.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.7.1a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.10.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.8.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.8.1a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.2"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.9.1a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.3"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.4"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.5"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.9.4a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "17.9.5b"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.6"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.6a"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.7"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.9.8"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.11.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.12.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.12.2"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.12.3"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.12.4"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.12.5"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.12.6"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.13.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.14.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.15.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.15.2"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.15.3"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.15.4"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.16.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.17.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.18.1"}}, {"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "17.18.2"}}], "enrichment": {"confidence": 88.0, "confidence_source": "matching", "scores": [{"score": 88.0, "source": "matching"}]}, "original": {"product": "Cisco IOS XE Software", "source": "cna", "vendor": "Cisco"}, "product": "ios_xe_software", "vendor": "cisco"}], "analysis": {"en": {"generated_at": "2026-03-26T14:35:50.347322+00:00", "value": {"mitigation_remediation": ["Apply the Cisco\u202fIOS\u202fXE Software patch or upgrade referenced in the Cisco security advisory", "Reboot the device after applying the patch to re\u2011enforce secure boot", "Verify that secure boot is enabled and that the device only loads Cisco\u2011signed images", "Conduct a review or inventory of installed binaries to confirm no unauthorized or modified firmware is present"], "summary": {"action": "Immediate Patch", "impact": "Boot\u2011time arbitrary code execution that bypasses secure boot"}, "threat_synthesis": {"affected_systems": "Affected systems include Cisco Catalyst\u202f9200 Series Switches, Cisco Catalyst\u202fESS9300 Embedded Series Switches, Cisco Catalyst\u202fIE9310 and IE9320 Rugged Series Switches, and Cisco\u202fIE3500 and IE3505 Rugged Series Switches. All run Cisco IOS\u202fXE Software; specific affected firmware versions are not disclosed in the advisory.", "description_and_impact": "The vulnerability lies in the bootloader of Cisco IOS\u202fXE Software on certain Cisco Catalyst and Rugged Series Switches. The bootloader performs integrity checks on the firmware image it loads, but these checks are insufficiently validated. An attacker with either level\u201115 local privileges or any physical access can modify the binaries read during boot, causing the device to execute malicious code and bypass the requirement that only Cisco\u2011signed images run, effectively breaking the secure boot chain of trust.", "risk_and_exploitability": "The CVSS score of 6.1 indicates moderate to high severity, yet the EPSS score is below 1%, suggesting a low current exploitation probability. Nonetheless, because the flaw allows arbitrary code execution at boot and can be triggered with physical possession or administrative credentials, it represents a serious risk. The vulnerability is not listed in the CISA KEV catalog, but the security advisory assigns it a high impact rating due to the loss of secure boot."}}}}, "created": "2026-03-26T11:42:45.139755+00:00", "title": "Bootloader Secure Boot Bypass on Cisco IOS\u202fXE Switches", "updated": "2026-03-27T09:46:59.296959+00:00", "vendors": ["cisco", "cisco$PRODUCT$ios_xe_software"]}