CVE-2026-33774

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control-plane of the device.\n\nOn MX platforms with \n\nMPC10, MPC11, LC4800 or LC9600\n\nline cards, and MX304, firewall filters applied on a loopback interface lo0.n (where n is a non-0 number) don't get executed when lo0.n is in the global VRF / default routing-instance.\n\n An affected configuration would be:\n\nuser@host# show configuration interfaces lo0 | display set\nset interfaces lo0 unit 1 family inet filter input <filter-name>\n\nwhere a firewall filter is applied to a non-0 loopback interface, but that loopback interface is not referred to in any routing-instance (RI) configuration, which implies that it's used in the default RI.\n\nThe issue can be observed with the CLI command:\n\nuser@device> show firewall counter filter <filter_name> \n\nnot showing any matches.\n\nThis issue affects Junos OS on MX Series:\n\n * all versions before 23.2R2-S6,\n * 23.4 versions before 23.4R2-S7,\n * 24.2 versions before 24.2R2,\n * 24.4 versions before 24.4R2.", "supportingMedia": 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"AND"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding engine (pfe) of Juniper Networks Junos OS on MX Series allows an unauthenticated, network-based attacker to bypass the configured firewall filter and access the control-plane of the device.\n\nOn MX platforms with \n\nMPC10, MPC11, LC4800 or LC9600\n\nline cards, and MX304, firewall filters applied on a loopback interface lo0.n (where n is a non-0 number) don't get executed when lo0.n is in the global VRF / default routing-instance.\n\n An affected configuration would be:\n\nuser@host# show configuration interfaces lo0 | display set\nset interfaces lo0 unit 1 family inet filter input <filter-name>\n\nwhere a firewall filter is applied to a non-0 loopback interface, but that loopback interface is not referred to in any routing-instance (RI) configuration, which implies that it's used in the default RI.\n\nThe issue can be observed with the CLI command:\n\nuser@device> show firewall counter filter <filter_name> \n\nnot showing any matches.\n\nThis issue affects Junos OS on MX Series:\n\n * all versions before 23.2R2-S6,\n * 23.4 versions before 23.4R2-S7,\n * 24.2 versions before 24.2R2,\n * 24.4 versions before 24.4R2."}, {"lang": "es", "value": "Una vulnerabilidad de \u2019Comprobaci\u00f3n Incorrecta de Condiciones Inusuales o Excepcionales\u2019 en el motor de reenv\u00edo de paquetes (pfe) de Juniper Networks Junos OS en la serie MX permite a un atacante no autenticado, basado en red, eludir el filtro de cortafuegos configurado y acceder al plano de control del dispositivo.\n\nEn plataformas MX con\n\ntarjetas de l\u00ednea MPC10, MPC11, LC4800 o LC9600, y MX304, los filtros de cortafuegos aplicados en una interfaz de bucle invertido lo0.n (donde n es un n\u00famero distinto de 0) no se ejecutan cuando lo0.n est\u00e1 en la VRF global / instancia de enrutamiento predeterminada.\n\nUna configuraci\u00f3n afectada ser\u00eda:\n\nuser@host# show configuration interfaces lo0 | display set\nset interfaces lo0 unit 1 family inet filter input [filter-name]\n\ndonde un filtro de cortafuegos se aplica a una interfaz de bucle invertido distinta de 0, pero esa interfaz de bucle invertido no se menciona en ninguna configuraci\u00f3n de instancia de enrutamiento (RI), lo que implica que se utiliza en la RI predeterminada.\n\nEl problema se puede observar con el comando CLI:\n\nuser@device> show firewall counter filter [filter_name]\n\nsin mostrar ninguna coincidencia.\n\nEste problema afecta a Junos OS en la serie MX:\n\n * todas las versiones anteriores a 23.2R2-S6,\n * versiones 23.4 anteriores a 23.4R2-S7,\n * versiones 24.2 anteriores a 24.2R2,\n * versiones 24.4 anteriores a 24.4R2."}], "id": "CVE-2026-33774", "lastModified": "2026-10-26T21:10:00.170", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 2.5, "source": "sirt@juniper.net", "type": "Secondary"}, {"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "LOW", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 1.4, "source": "nvd@nist.gov", "type": "Primary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "YES", "Recovery": "USER", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 6.9, "baseSeverity": "MEDIUM", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:Y/R:U/V:X/RE:L/U:X", "version": "4.0", "vulnAvailabilityImpact": "NONE", "vulnConfidentialityImpact": "LOW", "vulnIntegrityImpact": "LOW", "vulnerabilityResponseEffort": "LOW"}, "source": "sirt@juniper.net", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-33774", "options": [{"exploitation": "none"}, {"automatable": "no"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-04-10T14:14:09.835711Z", "version": "2.0.3"}}]}, "published": "2026-04-09T22:16:25.803", "references": [{"source": "sirt@juniper.net", "tags": ["Vendor Advisory"], "url": "https://kb.juniper.net/JSA107865"}], "sourceIdentifier": "sirt@juniper.net", "vulnStatus": "Analyzed", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-754"}], "source": "sirt@juniper.net", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": ["mx_series"], "status": "affected", "versions": {"scheme": "generic", "value": "[0,23.2R2-S6)"}}, {"platform": ["mx_series"], "status": "affected", "versions": {"scheme": "generic", "value": "[23.4,23.4R2-S7)"}}, {"platform": ["mx_series"], "status": "affected", "versions": {"scheme": "generic", "value": "[24.2,24.2R2)"}}, {"platform": ["mx_series"], "status": "affected", "versions": {"scheme": "generic", "value": "[24.4,24.4R2)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Junos OS", "source": "cna", "vendor": "Juniper Networks"}, "product": "junos_os", "vendor": "juniper_networks"}], "analysis": {"en": {"generated_at": "2026-04-09T23:52:36.437533+00:00", "value": {"mitigation_remediation": ["Upgrade Junos OS to at least 23.2R2\u2011S6, 23.4R2\u2011S7, 24.2R2, 24.4R2, 25.2R1, or any later release", "Rename any lo0.<n> (n\u22600) loopback interface used in the default routing instance to lo0.0 to trigger firewall filter enforcement", "Verify that firewall filter counters reflect activity on the lo0 interface to confirm the filter is now applied"], "summary": {"action": "Apply Patch", "impact": "Control\u2011plane bypass via firewall filter omission"}, "threat_synthesis": {"affected_systems": "The vulnerability affects Junipers\u2019 MX Series routers with MPC10, MPC11, LC4800, LC9600 line\u2011cards, and MX304. All Junos OS releases before 23.2R2\u2011S6, before 23.4R2\u2011S7, before 24.2R2, and before 24.4R2 are susceptible. It occurs when a firewall filter is attached to a lo0 unit that is not referenced in any routing\u2011instance configuration, meaning it is placed in the default routing instance.", "description_and_impact": "An improper check in the packet forwarding engine of Juniper Networks Junos OS on MX Series routers allows an unauthenticated, network\u2011based attacker to bypass firewall filters applied to non\u2011zero loopback interfaces (lo0.n, n\u22600) that reside in the default routing instance. The filter is never executed, enabling traffic destined for the control\u2011plane to reach the device without restriction. This flaw, classified as CWE\u2011754, effectively removes a critical access\u2011control barrier.", "risk_and_exploitability": "With a CVSS score of 6.9 and no EPSS data, the flaw is considered medium severity. Attackers need only network access to send traffic to the misconfigured lo0.n interface and do not require authentication, making exploitation straightforward for a nearby adversary. Since the control\u2011plane is exposed, an attacker could potentially access management interfaces or extract sensitive configuration if the device hosts critical network functions. The vulnerability is not listed in the CISA KEV catalog, but its impact warrants prompt remediation."}}}}, "created": "2026-04-10T08:36:58.309566+00:00", "updated": "2026-04-10T09:27:55.962629+00:00", "vendors": ["juniper_networks", "juniper_networks$PRODUCT$junos_os"]}