Critical 9.8Known exploited (CISA KEV)Published Jun 19, 2023

CVE-2023-27992The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware version…

Updated under an hour ago (2026-10-19 11:00 UTC)

Does this affect you?

It affects Zyxel NAS326 firmware and 2 other products. Add what you run to find out whether that includes you.

CISA lists it as known exploited since Jun 23, 2023; federal agencies had to remediate by Jul 14, 2023. Treat that date as your deadline.

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Every CVE for Zyxel NAS326 firmware

Exploited in the last 30 days

The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely by sending a crafted HTTP request.

CVSS: 9.8 CRITICAL (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): CWE-78
Known exploited: Added to CISA KEV Jun 23, 2023; federal remediation due Jul 14, 2023Apply updates per vendor instructions.
EPSS (exploitation in the next 30 days): 82.83% (percentile 100)
Assigned by: Zyxel
NVD analysis: Analyzed
Record last updated: Oct 21, 2025
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Zyxel NAS326 firmware zyxel:nas326_firmware (from the name)	before V5.21(AAZF.14)C0	CNA record
Zyxel NAS540 firmware zyxel:nas540_firmware (from the name)	before V5.21(AATB.11)C0	CNA record
Zyxel NAS542 firmware zyxel:nas542_firmware (from the name)	before V5.21(ABAG.11)C0	CNA record
zyxel nas326_firmware zyxel:nas326_firmware	before 5.21\(aazf.14\)c0	NVD
zyxel nas540_firmware zyxel:nas540_firmware	before 5.21\(aatb.11\)c0	NVD
zyxel nas542_firmware zyxel:nas542_firmware	before 5.21\(abag.11\)c0	NVD

References

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-pre-authentication-command-injection-vulnerability-in-nas-productspatch, vendor-advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-27992us-government-resource

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.