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CVE-2026-33774

Full vulnerability record from the local CVENow database.

Description

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. On MX platforms with MPC10, MPC11, LC4800 or LC9600 line 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. An affected configuration would be: user@host# show configuration interfaces lo0 | display set set interfaces lo0 unit 1 family inet filter input <filter-name> where 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. The issue can be observed with the CLI command: user@device> show firewall counter filter <filter_name> not showing any matches. This issue affects Junos OS on MX Series: * all versions before 23.2R2-S6, * 23.4 versions before 23.4R2-S7, * 24.2 versions before 24.2R2, * 24.4 versions before 24.4R2.

Severity
MEDIUM
CVSS score
6.9 (v4.0)
Vulnerability status
Analyzed
Source identifier
[email protected]
Published
2026-04-09 22:16:25.803000
Last modified
2026-10-26 21:10:00.170000
View original CVE JSON 
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  "id": "CVE-2026-33774",
  "sourceIdentifier": "[email protected]",
  "published": "2026-04-09T22:16:25.803",
  "lastModified": "2026-10-26T21:10:00.170",
  "vulnStatus": "Analyzed",
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      "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."
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      "value": "Una vulnerabilidad de ’Comprobación Incorrecta de Condiciones Inusuales o Excepcionales’ en el motor de reenvío 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 línea MPC10, MPC11, LC4800 o LC9600, y MX304, los filtros de cortafuegos aplicados en una interfaz de bucle invertido lo0.n (donde n es un número distinto de 0) no se ejecutan cuando lo0.n está en la VRF global / instancia de enrutamiento predeterminada.\n\nUna configuración afectada sería:\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 configuración 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."
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