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Weekly Signal
Live intelligence Updated 19 Aug 2026 · 20:27 UTC

Zyxel · Multiple Network-Attached Storage (NAS) Devices, Nas326 Firmware, Nas540 Firmware +1 more

CVE-2023-27992

Zyxel Multiple NAS Devices Command Injection Vulnerability

Recommended action

Validate affected assets and exposure now, then remediate on an accelerated schedule. Apply updates per vendor instructions.

View response plan
CVSS9.8
EPSS84.2%
KEVYes
ExploitationConfirmed exploitation
RemediationExplicit patch identified ↓

Assessment

Why it matters

CISA lists this vulnerability as known to be exploited; exploitation is confirmed; EPSS is 84.2%; technical severity is CVSS 9.8.

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.

Who should care

  • Teams operating Multiple Network-Attached Storage (NAS) Devices, Nas326 Firmware, Nas540 Firmware +1 more
  • Vulnerability and exposure management teams
  • Security operations teams monitoring exploitation activity

Response plan

What I would do

  1. Confirm whether Multiple Network-Attached Storage (NAS) Devices, Nas326 Firmware, Nas540 Firmware +1 more is present in the environment.
  2. Identify affected versions and establish whether vulnerable services are exposed or reachable.
  3. Apply updates per vendor instructions.
  4. Review relevant security telemetry for evidence of attempted or successful exploitation.
  5. Document the remediation decision and track it to verified completion.

Treatment intelligence

Remediation intelligence

Not yet verified

Vendor sources are listed before government and third-party guidance. Confirm product applicability and change prerequisites before deployment.

Verification noteAutomated link verification has not completed for this guidance yet.

Patch

Required Action

Technical details

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-78
Affected versions
Zyxel Multiple Network-Attached Storage (NAS) Devices; Zyxel Nas326 Firmware (End Excluding 5.21\(aazf.14\)c0); Zyxel Nas540 Firmware (End Excluding 5.21\(aatb.11\)c0); Zyxel Nas542 Firmware (End Excluding 5.21\(abag.11\)c0)
Fixed versions
Zyxel Nas326 Firmware (Fixed from 5.21\(aazf.14\)c0); Zyxel Nas540 Firmware (Fixed from 5.21\(aatb.11\)c0); Zyxel Nas542 Firmware (Fixed from 5.21\(abag.11\)c0)
Published
19 June 2023
Attack vector
Network
Privileges required
None
User interaction
None

Signal timeline

  1. CVE published
  2. Added to CISA KEV
  3. Latest EPSS score: 84.2%
  4. Signal calculated at 83

External references

Live public intelligence This assessment combines public-source evidence. Validate the affected product, version and exposure against your own environment before making a risk decision.