What’s Vulnerable › Vulnerabilities
CVE-2020-13364
- Severity: high (CVSS 8.8 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 1.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2020-08-06 · updated 2026-06-17
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.
Affected products
- Zyxel NAS326 firmware: before v5.21\(aazf.9\)c0 — fixed in v5.21\(aazf.9\)c0
- Zyxel Nas520 Firmware: before v5.21\(aasz.5\)c0 — fixed in v5.21\(aasz.5\)c0
- Zyxel NAS540 firmware: before v5.21\(aatb.6\)c0 — fixed in v5.21\(aatb.6\)c0
- Zyxel NAS542 firmware: before v5.21\(abag.6\)c0 — fixed in v5.21\(abag.6\)c0
How to fix
Upgrade to a fixed version: Zyxel NAS326 firmware v5.21\(aazf.9\)c0; Zyxel Nas520 Firmware v5.21\(aasz.5\)c0; Zyxel NAS540 firmware v5.21\(aatb.6\)c0; Zyxel NAS542 firmware v5.21\(abag.6\)c0. Check the vendor advisory for mitigations.
References
- https://www.zyxel.com/support/Zyxel-security-advisory-for-NAS-remote-access-vulnerability.shtml
- https://www.zyxel.com/us/en/support/security_advisories.shtml
- https://www.zyxel.com/support/Zyxel-security-advisory-for-NAS-remote-access-vulnerability.shtml
- https://www.zyxel.com/us/en/support/security_advisories.shtml
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