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
CWE
  • CWE-754 - Improper Check for Unusual or Exceptional Conditions
Assigner
References
Impacted products
Vendor Product Version
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)
Create a notification for this product.
Date Public ?
2026-04-08 16:00
Show details on NVD website
To clipboard 

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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.\\n\\nThe issue can be observed with the CLI command:\\n\\nuser@device\u003e show firewall counter filter \u003cfilter_name\u003e \\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\": [{\"type\": \"text/html\", \"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\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-754\", \"description\": \"CWE-754 Improper Check for Unusual or Exceptional Conditions\"}]}], \"providerMetadata\": {\"orgId\": \"8cbe9d5a-a066-4c94-8978-4b15efeae968\", \"shortName\": \"juniper\", \"dateUpdated\": \"2026-04-09T21:34:21.126Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-33774\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-04-10T14:14:24.774Z\", \"dateReserved\": \"2026-03-23T19:46:13.668Z\", \"assignerOrgId\": \"8cbe9d5a-a066-4c94-8978-4b15efeae968\", \"datePublished\": \"2026-04-09T21:34:21.126Z\", \"assignerShortName\": \"juniper\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Detection rules are retrieved from Rulezet.