{"id":"CVE-2025-21594","aliases":["EUVD-2025-10531","GHSA-393v-j9q3-p63r"],"status":"published","title":"Junos OS: MX Series: In DS-lite and NAT scenario receipt of crafted IPv6 traffic causes port block","description":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS).\n\nIn a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover.\nFollowing is the command to identify the issue: \n\n\n    user@host\u003e show services nat source port-block \n    Host_IP                       External_IP                    Port_Block      Ports_Used/        Block_State/\n                                                               Range             Ports_Total        Left_Time(s)\n    2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-        \u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003eport still usedThis issue affects Junos OS on MX Series: \n\n  *  from 21.2 before 21.2R3-S8, \n  *  from 21.4 before 21.4R3-S7, \n  *  from 22.1 before 22.1R3-S6, \n  *  from 22.2 before 22.2R3-S4, \n  *  from 22.3 before 22.3R3-S3, \n  *  from 22.4 before 22.4R3-S2, \n  *  from 23.2 before 23.2R2-S1, \n  *  from 23.4 before 23.4R1-S2, 23.4R2.\n\n\nThis issue does not affect versions before 20.2R1.","severity":{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/R:U","level":"high","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-10","score":0.00433,"percentile":0.37871,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-754"],"published":"2025-04-09T19:49:41Z","modified":"2026-06-17T08:43:48Z","products":[{"vendor":"juniper","product":"junos"},{"vendor":"juniper networks","product":"junos os"}],"references":[{"url":"https://supportportal.juniper.net/JSA96449","tags":["vendor-advisory","Vendor Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2025-21594"},{"url":"https://github.com/advisories/GHSA-393v-j9q3-p63r"}],"sources":{"cve":[{"id":"CVE-2025-21594","title":"Junos OS: MX Series: In DS-lite and NAT scenario receipt of crafted IPv6 traffic causes port block","description":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS).\n\nIn a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover.\nFollowing is the command to identify the issue: \n\n\n    user@host\u003e show services nat source port-block \n    Host_IP                       External_IP                    Port_Block      Ports_Used/        Block_State/\n                                                               Range             Ports_Total        Left_Time(s)\n    2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-        \u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003eport still usedThis issue affects Junos OS on MX Series: \n\n  *  from 21.2 before 21.2R3-S8, \n  *  from 21.4 before 21.4R3-S7, \n  *  from 22.1 before 22.1R3-S6, \n  *  from 22.2 before 22.2R3-S4, \n  *  from 22.3 before 22.3R3-S3, \n  *  from 22.4 before 22.4R3-S2, \n  *  from 23.2 before 23.2R2-S1, \n  *  from 23.4 before 23.4R1-S2, 23.4R2.\n\n\nThis issue does not affect versions before 20.2R1.","status":"published","published":"2025-04-09T19:49:41.391Z","modified":"2025-04-10T13:14:00.65Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/R:U","level":"high","assessor":"cna"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"cna"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T14:32:32.30152Z"}],"euvd":[{"id":"EUVD-2025-10531","description":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS).\n\nIn a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover.\nFollowing is the command to identify the issue: \n\n\n    user@host\u003e show services nat source port-block \n    Host_IP                       External_IP                    Port_Block      Ports_Used/        Block_State/\n                                                               Range             Ports_Total        Left_Time(s)\n    2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-        \u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003eport still usedThis issue affects Junos OS on MX Series: \n\n  *  from 21.2 before 21.2R3-S8, \n  *  from 21.4 before 21.4R3-S7, \n  *  from 22.1 before 22.1R3-S6, \n  *  from 22.2 before 22.2R3-S4, \n  *  from 22.3 before 22.3R3-S3, \n  *  from 22.4 before 22.4R3-S2, \n  *  from 23.2 before 23.2R2-S1, \n  *  from 23.4 before 23.4R1-S2, 23.4R2.\n\n\nThis issue does not affect versions before 20.2R1.","status":"published","published":"2025-04-09T19:49:41Z","modified":"2025-04-10T13:14:00Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/R:U","level":"high"}],"updated_at":"2026-11-02T20:52:37.204811Z"}],"ghsa":[{"id":"GHSA-393v-j9q3-p63r","title":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet...","description":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS).\n\nIn a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover.\nFollowing is the command to identify the issue: \n\n\n    user@host\u003e show services nat source port-block \n    Host_IP                       External_IP                    Port_Block      Ports_Used/        Block_State/\n                                                               Range             Ports_Total        Left_Time(s)\n    2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-        \u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003eport still usedThis issue affects Junos OS on MX Series: \n\n  *  from 21.2 before 21.2R3-S8, \n  *  from 21.4 before 21.4R3-S7, \n  *  from 22.1 before 22.1R3-S6, \n  *  from 22.2 before 22.2R3-S4, \n  *  from 22.3 before 22.3R3-S3, \n  *  from 22.4 before 22.4R3-S2, \n  *  from 23.2 before 23.2R2-S1, \n  *  from 23.4 before 23.4R1-S2, 23.4R2.\n\n\nThis issue does not affect versions before 20.2R1.","status":"published","published":"2025-04-09T21:31:43Z","modified":"2025-04-09T21:31:50Z","cvss":[{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high"},{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/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:X/R:U/V:X/RE:X/U:X","level":"high"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T15:01:03.275422Z"}],"nvd":[{"id":"CVE-2025-21594","description":"An Improper Check for Unusual or Exceptional Conditions vulnerability in the pfe (packet forwarding engine) of Juniper Networks Junos OS on MX Series causes a port within a pool to be blocked leading to Denial of Service (DoS).\n\nIn a DS-Lite (Dual-Stack Lite) and NAT (Network Address Translation) scenario, when crafted IPv6 traffic is received and prefix-length is set to 56, the ports assigned to the user will not be freed.  Eventually, users cannot establish new connections. Affected FPC/PIC need to be manually restarted to recover.\nFollowing is the command to identify the issue: \n\n\n    user@host\u003e show services nat source port-block \n    Host_IP                       External_IP                    Port_Block      Ports_Used/        Block_State/\n                                                               Range             Ports_Total        Left_Time(s)\n    2001::                        x.x.x.x                     58880-59391     256/256*1         Active/-        \u003e\u003e\u003e\u003e\u003e\u003e\u003e\u003eport still usedThis issue affects Junos OS on MX Series: \n\n  *  from 21.2 before 21.2R3-S8, \n  *  from 21.4 before 21.4R3-S7, \n  *  from 22.1 before 22.1R3-S6, \n  *  from 22.2 before 22.2R3-S4, \n  *  from 22.3 before 22.3R3-S3, \n  *  from 22.4 before 22.4R3-S2, \n  *  from 23.2 before 23.2R2-S1, \n  *  from 23.4 before 23.4R1-S2, 23.4R2.\n\n\nThis issue does not affect versions before 20.2R1.","status":"published","published":"2025-04-09T20:15:25.62Z","modified":"2026-06-17T08:43:48.513Z","cvss":[{"version":"4.0","score":8.7,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L/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:X/R:U/V:X/RE:X/U:X","level":"high","assessor":"secondary"},{"version":"3.1","score":7.5,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","level":"high","assessor":"secondary"}],"cwes":["CWE-754"],"updated_at":"2026-11-02T14:11:00.087098Z"}]}}