CVE-2026-33774 (GCVE-0-2026-33774)

Vulnerability from cvelistv5 – Published: 2026-04-09 21:34 – Updated: 2026-04-10 14:14
VLAI
Title
Junos OS: MX Series: Firewall filters on lo0.<non-0> in the default routing instance are not in effect
Summary
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
6.5 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
6.9 (Medium)
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/AU:Y/R:U/RE:L
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-04-10 14:14 UTC
CWE
  • CWE-754 - Improper Check for Unusual or Exceptional Conditions
Assigner
juniper CNA under the mitre root
CNA scorecard B 84/100 over 193 records in the last 180 days details
References
URL Tags
https://kb.juniper.net/JSA107865 vendor-advisory
Impacted products
Vendor Product Version CPE status
Juniper Networks Junos OS Affected: 0 , < 23.2R2-S6 (semver)
Affected: 23.4 , < 23.4R2-S7 (semver)
Affected: 24.2 , < 24.2R2 (semver)
Affected: 24.4 , < 24.4R2 (semver)
guessed Create a notification for this product.
Date Public
2026-04-08 16:00
Show details on NVD website
To clipboard 

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            "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\u003e 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",
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      "source": "Red Hat CSAF VEX",
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      "title": "Junos OS: MX Series: Firewall filters on lo0.\u003cnon-0\u003e in the default routing instance are not in effect",
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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.\u003cbr\u003e\u003cbr\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003eOn MX platforms with \n\n\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003eMPC10, MPC11, LC4800 or LC9600\u003c/span\u003e\n\nline cards, and MX304, firewall filters applied on a loopback interface lo0.n (where n is a non-0 number) don\u0027t get executed when lo0.n is in the global VRF / default routing-instance.\u003cbr\u003e\u003cbr\u003e An affected configuration would be:\u003cbr\u003e\u003c/span\u003e\u003ctt\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003euser@host# show configuration interfaces lo0 | display set\u003cbr\u003eset interfaces lo0 unit 1 family inet filter input \u0026lt;filter-name\u0026gt;\u003c/span\u003e\u003c/tt\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003e\u003cbr\u003e\u003cbr\u003ewhere 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\u0027s used in the default RI.\u003cbr\u003e\u003cbr\u003eThe issue can be observed with the CLI command:\u003cbr\u003e\u003cbr\u003e\u003c/span\u003e\u003ctt\u003e\u003cspan style=\"background-color: rgb(255, 255, 255);\"\u003euser@device\u0026gt; show firewall counter filter \u0026lt;filter_name\u0026gt;\u003c/span\u003e\u003c/tt\u003e \u003cbr\u003e\u003cbr\u003enot showing any matches.\u003cbr\u003e\u003cbr\u003e\u003cp\u003eThis issue affects Junos OS on MX Series:\u003c/p\u003e\u003cul\u003e\u003cli\u003eall versions before 23.2R2-S6,\u003c/li\u003e\u003cli\u003e23.4 versions before 23.4R2-S7,\u003c/li\u003e\u003cli\u003e24.2 versions before 24.2R2,\u003c/li\u003e\u003cli\u003e24.4 versions before 24.4R2.\u003c/li\u003e\u003c/ul\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"
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}



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