CVE-2020-13364

Name: CVE-2020-13364
Creator: NVD / NIST
Published: 2020-08-06T17:15:10.83+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.8/10EPSS 1.15%

Last modified Jun 17, 2026

CVE-2020-13364 is a high-severity vulnerability rated 8.8/10 on the CVSS scale. 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.. EPSS estimates a 1.15% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

8.8/10

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

1.15%

62.9th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Vendor	Product	Versions
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

References

https://www.zyxel.com/support/Zyxel-security-advisory-for-NAS-remote-access-vulnerability.shtmlVendor Advisory
https://www.zyxel.com/us/en/support/security_advisories.shtmlVendor Advisory
https://www.zyxel.com/support/Zyxel-security-advisory-for-NAS-remote-access-vulnerability.shtmlVendor Advisory
https://www.zyxel.com/us/en/support/security_advisories.shtmlVendor Advisory

Timeline

Published: Aug 6, 2020
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2020-13364?

How severe is CVE-2020-13364?

CVE-2020-13364 has a CVSS score of 8.8/10 (HIGH severity). The EPSS model estimates a 1.15% probability of exploitation in the next 30 days.

How do I fix CVE-2020-13364?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2020-13364?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST