{"id":"CVE-2020-13364","aliases":["EUVD-2020-5623","GHSA-cwv4-27xg-6829"],"status":"published","title":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects...","description":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects NAS520 V5.21(AASZ.4)C0, V5.21(AASZ.0)C0, V5.11(AASZ.3)C0, and V5.11(AASZ.0)C0; NAS542 V5.11(ABAG.0)C0, V5.20(ABAG.1)C0, and V5.21(ABAG.3)C0; NSA325 v2_V4.81(AALS.0)C0 and V4.81(AAAJ.1)C0; NSA310 4.22(AFK.0)C0 and 4.22(AFK.1)C0; NAS326 V5.21(AAZF.8)C0, V5.11(AAZF.4)C0, V5.11(AAZF.2)C0, and V5.11(AAZF.3)C0; NSA310S V4.75(AALH.2)C0; NSA320S V4.75(AANV.2)C0 and V4.75(AANV.1)C0; NSA221 V4.41(AFM.1)C0; and NAS540 V5.21(AATB.5)C0 and V5.21(AATB.3)C0.","severity":{"version":"3.0","score":6.5,"vector":"CVSS:3.0/AC:L/AV:N/A:N/C:L/I:L/PR:N/S:U/UI:N","level":"medium","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-11","score":0.01151,"percentile":0.67351,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":false},"cwes":["CWE-269"],"published":"2020-08-06T16:54:43Z","modified":"2026-06-17T02:53:01Z","products":[{"vendor":"zyxel","product":"nas326_firmware"},{"vendor":"zyxel","product":"nas520_firmware"},{"vendor":"zyxel","product":"nas540_firmware"},{"vendor":"zyxel","product":"nas542_firmware"}],"references":[{"url":"https://www.zyxel.com/us/en/support/security_advisories.shtml","tags":["x_refsource_MISC","x_transferred","Vendor Advisory"]},{"url":"https://www.zyxel.com/support/Zyxel-security-advisory-for-NAS-remote-access-vulnerability.shtml","tags":["x_refsource_MISC","x_transferred","Vendor Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2020-13364"},{"url":"https://github.com/advisories/GHSA-cwv4-27xg-6829"}],"sources":{"cve":[{"id":"CVE-2020-13364","description":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects NAS520 V5.21(AASZ.4)C0, V5.21(AASZ.0)C0, V5.11(AASZ.3)C0, and V5.11(AASZ.0)C0; NAS542 V5.11(ABAG.0)C0, V5.20(ABAG.1)C0, and V5.21(ABAG.3)C0; NSA325 v2_V4.81(AALS.0)C0 and V4.81(AAAJ.1)C0; NSA310 4.22(AFK.0)C0 and 4.22(AFK.1)C0; NAS326 V5.21(AAZF.8)C0, V5.11(AAZF.4)C0, V5.11(AAZF.2)C0, and V5.11(AAZF.3)C0; NSA310S V4.75(AALH.2)C0; NSA320S V4.75(AANV.2)C0 and V4.75(AANV.1)C0; NSA221 V4.41(AFM.1)C0; and NAS540 V5.21(AATB.5)C0 and V5.21(AATB.3)C0.","status":"published","published":"2020-08-06T16:54:43Z","modified":"2024-08-04T12:18:18.253Z","cvss":[{"version":"3.0","score":6.5,"vector":"CVSS:3.0/AC:L/AV:N/A:N/C:L/I:L/PR:N/S:U/UI:N","level":"medium","assessor":"cna"}],"updated_at":"2026-11-02T14:35:53.868619Z"}],"euvd":[{"id":"EUVD-2020-5623","description":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects NAS520 V5.21(AASZ.4)C0, V5.21(AASZ.0)C0, V5.11(AASZ.3)C0, and V5.11(AASZ.0)C0; NAS542 V5.11(ABAG.0)C0, V5.20(ABAG.1)C0, and V5.21(ABAG.3)C0; NSA325 v2_V4.81(AALS.0)C0 and V4.81(AAAJ.1)C0; NSA310 4.22(AFK.0)C0 and 4.22(AFK.1)C0; NAS326 V5.21(AAZF.8)C0, V5.11(AAZF.4)C0, V5.11(AAZF.2)C0, and V5.11(AAZF.3)C0; NSA310S V4.75(AALH.2)C0; NSA320S V4.75(AANV.2)C0 and V4.75(AANV.1)C0; NSA221 V4.41(AFM.1)C0; and NAS540 V5.21(AATB.5)C0 and V5.21(AATB.3)C0.","status":"published","published":"2020-08-06T16:54:43Z","modified":"2024-08-04T12:18:18Z","cvss":[{"version":"3.0","score":6.5,"vector":"CVSS:3.0/AC:L/AV:N/A:N/C:L/I:L/PR:N/S:U/UI:N","level":"medium"}],"updated_at":"2026-11-03T03:07:37.76906Z"}],"ghsa":[{"id":"GHSA-cwv4-27xg-6829","title":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects...","description":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects NAS520 V5.21(AASZ.4)C0, V5.21(AASZ.0)C0, V5.11(AASZ.3)C0, and V5.11(AASZ.0)C0; NAS542 V5.11(ABAG.0)C0, V5.20(ABAG.1)C0, and V5.21(ABAG.3)C0; NSA325 v2_V4.81(AALS.0)C0 and V4.81(AAAJ.1)C0; NSA310 4.22(AFK.0)C0 and 4.22(AFK.1)C0; NAS326 V5.21(AAZF.8)C0, V5.11(AAZF.4)C0, V5.11(AAZF.2)C0, and V5.11(AAZF.3)C0; NSA310S V4.75(AALH.2)C0; NSA320S V4.75(AANV.2)C0 and V4.75(AANV.1)C0; NSA221 V4.41(AFM.1)C0; and NAS540 V5.21(AATB.5)C0 and V5.21(AATB.3)C0.","status":"published","published":"2022-05-24T17:25:00Z","modified":"2023-01-29T05:04:03Z","cwes":["CWE-269"],"updated_at":"2026-11-02T14:45:27.507739Z"}],"nvd":[{"id":"CVE-2020-13364","description":"A backdoor in certain Zyxel products allows remote TELNET access via a CGI script. This affects NAS520 V5.21(AASZ.4)C0, V5.21(AASZ.0)C0, V5.11(AASZ.3)C0, and V5.11(AASZ.0)C0; NAS542 V5.11(ABAG.0)C0, V5.20(ABAG.1)C0, and V5.21(ABAG.3)C0; NSA325 v2_V4.81(AALS.0)C0 and V4.81(AAAJ.1)C0; NSA310 4.22(AFK.0)C0 and 4.22(AFK.1)C0; NAS326 V5.21(AAZF.8)C0, V5.11(AAZF.4)C0, V5.11(AAZF.2)C0, and V5.11(AAZF.3)C0; NSA310S V4.75(AALH.2)C0; NSA320S V4.75(AANV.2)C0 and V4.75(AANV.1)C0; NSA221 V4.41(AFM.1)C0; and NAS540 V5.21(AATB.5)C0 and V5.21(AATB.3)C0.","status":"published","published":"2020-08-06T17:15:10.83Z","modified":"2026-06-17T02:53:01.923Z","cvss":[{"version":"3.1","score":8.8,"vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","level":"high","assessor":"primary"},{"version":"3.0","score":6.5,"vector":"CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N","level":"medium","assessor":"secondary"},{"version":"2.0","score":9,"vector":"AV:N/AC:L/Au:S/C:C/I:C/A:C","level":"high","assessor":"primary"}],"updated_at":"2026-11-02T14:06:10.994748Z"}]}}