A backdoor in certain Zyxel products allows remote TELNET access via a CGI script.
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- No fix listed
Attack profile from CVSS 3.1 · NVD. Fix status from CNA.
Summary
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.
Why it matters now
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
CPE configurations NVD · 8
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:o:zyxel:nas326_firmware:*:*:*:*:*:*:*:* | before v5.21\(aazf.9\)c0 | Vulnerable | Zyxel |
| cpe:2.3:h:zyxel:nas326:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Zyxel |
| cpe:2.3:o:zyxel:nas520_firmware:*:*:*:*:*:*:*:* | before v5.21\(aasz.5\)c0 | Vulnerable | Zyxel |
| cpe:2.3:h:zyxel:nas520:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Zyxel |
| cpe:2.3:o:zyxel:nas540_firmware:*:*:*:*:*:*:*:* | before v5.21\(aatb.6\)c0 | Vulnerable | Zyxel |
| cpe:2.3:h:zyxel:nas540:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Zyxel |
| cpe:2.3:o:zyxel:nas542_firmware:*:*:*:*:*:*:*:* | before v5.21\(abag.6\)c0 | Vulnerable | Zyxel |
| cpe:2.3:h:zyxel:nas542:-:*:*:*:*:*:*:* | not specified by NVD | Running on | Zyxel |
- cpe:2.3:o:zyxel:nas326_firmware:*:*:*:*:*:*:*:* Versions before v5.21\(aazf.9\)c0 Vulnerable ·Zyxel
- cpe:2.3:h:zyxel:nas326:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Zyxel
- cpe:2.3:o:zyxel:nas520_firmware:*:*:*:*:*:*:*:* Versions before v5.21\(aasz.5\)c0 Vulnerable ·Zyxel
- cpe:2.3:h:zyxel:nas520:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Zyxel
- cpe:2.3:o:zyxel:nas540_firmware:*:*:*:*:*:*:*:* Versions before v5.21\(aatb.6\)c0 Vulnerable ·Zyxel
- cpe:2.3:h:zyxel:nas540:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Zyxel
- cpe:2.3:o:zyxel:nas542_firmware:*:*:*:*:*:*:*:* Versions before v5.21\(abag.6\)c0 Vulnerable ·Zyxel
- cpe:2.3:h:zyxel:nas542:-:*:*:*:*:*:*:* Versions not specified by NVD Running on ·Zyxel
Remediation
No fixed version listed by the sources yet.
Timeline
- 2026-10-02 Threatist record created from CVE-2020-13364
- 2026-10-03 Alias added: GHSA-cwv4-27xg-6829
References
More Zyxel Nas326 Firmware vulnerabilities
- TI-2023-12582 OS command injection in Zyxel NAS326 firmware KEVCVSS 3.1CRITICAL 9.8
- TI-2020-07267 OS command injection in Zyxel NAS326 KEVCVSS 3.1CRITICAL 9.8
- TI-2024-19735 OS command injection in Zyxel NAS326 firmware CVSS 3.1CRITICAL 9.8
- TI-2024-19736 OS command injection in Zyxel NAS326 firmware CVSS 3.1CRITICAL 9.8
- TI-2023-04130 OS command injection in Zyxel NAS326 firmware CVSS 3.1CRITICAL 9.8
- TI-2023-04129 OS command injection in Zyxel NAS326 firmware CVSS 3.1CRITICAL 9.8
Sources
- CVE-2020-13364 · CVE Program
- CVE-2020-13364 · NVD
- FIRST EPSS
- GHSA-cwv4-27xg-6829 · GitHub Advisory Database · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences