{"id":"CVE-2026-33774","aliases":["EUVD-2026-21195","GHSA-3p5v-chx4-4483"],"status":"published","title":"Junos OS: MX Series: Firewall filters on lo0.\u003cnon-0\u003e 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 \u003cfilter-name\u003e\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\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.","severity":{"version":"4.0","score":6.9,"vector":"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","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-12","score":0.0018,"percentile":0.07682,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-754"],"published":"2026-04-09T21:34:21Z","modified":"2026-10-26T21:10:00Z","products":[{"vendor":"juniper","product":"junos"},{"vendor":"juniper networks","product":"junos os"}],"references":[{"url":"https://kb.juniper.net/JSA107865","tags":["vendor-advisory","Vendor Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33774"},{"url":"https://github.com/advisories/GHSA-3p5v-chx4-4483"}],"sources":{"cve":[{"id":"CVE-2026-33774","title":"Junos OS: MX Series: Firewall filters on lo0.\u003cnon-0\u003e 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 \u003cfilter-name\u003e\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\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.","status":"published","published":"2026-04-09T21:34:21.126Z","modified":"2026-04-10T14:14:24.774Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium","assessor":"cna"},{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","level":"medium","assessor":"cna"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T14:20:08.009733Z"}],"euvd":[{"id":"EUVD-2026-21195","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 \u003cfilter-name\u003e\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\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.","status":"published","published":"2026-04-09T21:34:21Z","modified":"2026-04-10T14:14:24Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium"}],"updated_at":"2026-11-02T19:24:29.850635Z"}],"ghsa":[{"id":"GHSA-3p5v-chx4-4483","title":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the packet forwarding...","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 \u003cfilter-name\u003e\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\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.","status":"published","published":"2026-04-10T00:30:29Z","modified":"2026-04-10T00:30:37Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium"},{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","level":"medium"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T15:07:24.354029Z"}],"nvd":[{"id":"CVE-2026-33774","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 \u003cfilter-name\u003e\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\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.","status":"published","published":"2026-04-09T22:16:25.803Z","modified":"2026-10-26T21:10:00.17Z","cvss":[{"version":"4.0","score":6.9,"vector":"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","level":"medium","assessor":"secondary"},{"version":"3.1","score":6.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","level":"medium","assessor":"secondary"},{"version":"3.1","score":5.3,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N","level":"medium","assessor":"primary"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T14:12:13.902911Z"}]}}