{"api_version":"1","generated_at":"2026-04-22T19:50:47+00:00","cve":"CVE-2026-33774","urls":{"html":"https://cve.report/CVE-2026-33774","api":"https://cve.report/api/cve/CVE-2026-33774.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-33774","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-33774"},"summary":{"title":"Junos OS: MX Series: Firewall filters on lo0.<non-0> in the default routing instance are not in effect","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.\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.","state":"PUBLISHED","assigner":"juniper","published_at":"2026-04-09 22:16:25","updated_at":"2026-04-13 15:02:27"},"problem_types":["CWE-754","CWE-754 CWE-754 Improper Check for Unusual or Exceptional 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MX Series allows an unauthenticated, network-based attacker to bypass the configured firewall filter and access the control-plane of the device.<br><br><span style=\"background-color: rgb(255, 255, 255);\">On MX platforms with \n\n<span style=\"background-color: rgb(255, 255, 255);\">MPC10, MPC11, LC4800 or LC9600</span>\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.<br><br> An affected configuration would be:<br></span><tt><span style=\"background-color: rgb(255, 255, 255);\"><br>user@host# show configuration interfaces lo0 | display set<br>set interfaces lo0 unit 1 family inet filter input &lt;filter-name&gt;</span></tt><span style=\"background-color: rgb(255, 255, 255);\"><br><br>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.<br><br>The issue can be observed with the CLI command:<br><br></span><tt><span style=\"background-color: rgb(255, 255, 255);\">user@device&gt; show firewall counter filter &lt;filter_name&gt;</span></tt> <br><br>not showing any matches.<br><br><p>This issue affects Junos OS on MX Series:</p><ul><li>all versions before 23.2R2-S6,</li><li>23.4 versions before 23.4R2-S7,</li><li>24.2 versions before 24.2R2,</li><li>24.4 versions before 24.4R2.</li></ul><p><br></p>"}],"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."}],"exploits":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"Juniper SIRT is not aware of any malicious exploitation of this vulnerability."}],"value":"Juniper SIRT is not aware of any malicious exploitation 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style=\"background-color: rgb(255, 255, 255);\">Renaming the lo0 logical unit used in the default routing instance from non-0 to 0 resolves this issue.</span><br>"}],"value":"Renaming the lo0 logical unit used in the default routing instance from non-0 to 0 resolves this issue."}],"x_generator":{"engine":"Vulnogram 0.1.0-dev"}}},"cveMetadata":{"assignerOrgId":"8cbe9d5a-a066-4c94-8978-4b15efeae968","assignerShortName":"juniper","cveId":"CVE-2026-33774","datePublished":"2026-04-09T21:34:21.126Z","dateReserved":"2026-03-23T19:46:13.668Z","dateUpdated":"2026-04-10T14:14:24.774Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-04-09 22:16:25","lastModifiedDate":"2026-04-13 15:02:27","problem_types":["CWE-754","CWE-754 CWE-754 Improper Check for Unusual or Exceptional 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OS: MX Series: Firewall filters on lo0.<non-0> in the defa","CVE":"CVE-2026-33774","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"33774","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Junos OS: MX Series: Firewall filters on lo0.<non-0> in the defa"}]}}}