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Vulnerabilities/CVE-2023-27992Public Intelligence Dossier
Source: zyxel · Limited verification•Last verified: •Collection Degraded
CVE-2023-27992ListedCRITICAL (raw)CVSS 9.8CWE-78

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.

Published: 19 Jun 2023•Last updated: 17 Jun 2026, 11:16 AM IST•Source identifier: security@zyxel.com.tw
Dossier completeness: source-provided sections 3 / 3 · rule guidance available. Missing source facts count as incomplete.
Official source
CISA KEV catalog
Listed
Added23 Jun 2023
Due14 Jul 2023
RansomwareUnknown
CVSS score
9.8CRITICAL (raw)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Metric sourcesecurity@zyxel.com.tw
EPSS probability
82.3%0.823
Percentile100th
Weakness type
CWE-78
No further CWE recorded
Remediation
Patch status unknown
No fixed version or KB recorded

Why It Matters

Analysis dossier

Why It Matters

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.

SOC priority

Immediate Attention

Actively exploited (source statement)

Yes

Publicly disclosed

Unknown

Risk basis: CISA KEV exploitation signal; CRITICAL severity; Source-confirmed exploitation or CISA KEV/ransomware metadata

Affected Products & Remediation

3 source-backed products
Affected products and versions (source)
  • zyxel nas326 firmware · < 5.21\(aazf.14\)c0 · NVD CPE · Source
  • zyxel nas540 firmware · < 5.21\(aatb.11\)c0 · NVD CPE · Source
  • zyxel nas542 firmware · < 5.21\(abag.11\)c0 · NVD CPE · Source
NVD applicability prerequisites: cpe:2.3:h:zyxel:nas326:-:*:*:*:*:*:*:*, cpe:2.3:h:zyxel:nas540:-:*:*:*:*:*:*:*, cpe:2.3:h:zyxel:nas542:-:*:*:*:*:*:*:*. These are conditions, not proof that an environment is exposed or unaffected.
Recorded patch / KBNot provided by source

Vendor or catalog guidance (source)

  • CISA KEV: Apply updates per vendor instructions.

Known exploitation (source facts)

Only what a source states. Unknown means no source has said either way; it is not "not exploited".

CISA KEV
Listed
Exploited (source statement)
Yes
Publicly disclosed (source)
Unknown

CISA required action: Apply updates per vendor instructions.

Suggested hunting (rule-based inference)

SecOps Signal recommendation (rule-based inference). These steps are hunting hypotheses from the vulnerability class; they do not state or imply that exploitation occurred here or anywhere.

Matched kev-network-exposure (CVSS AV:N, CISA KEV Listed); command-injection (CWE-78)

Exposure

  1. Identify assets with the exact CVE and confirm the affected product/version against the advisory.Telemetry: DeviceTvmSoftwareVulnerabilities · KEV listing raises urgency, but inventory is needed to establish local exposure. · Rule kev-network-exposure
  2. Identify installations of the affected product and compare versions with the advisory.Telemetry: DeviceTvmSoftwareVulnerabilities · A weakness class does not establish local exposure. · Rule command-injection

Exploitation evidence

  1. Review relevant edge or application access logs for unusual requests around the advisory window.Telemetry: CommonSecurityLog · Log review is a hunting hypothesis; KEV listing alone does not show local exploitation. · Rule kev-network-exposure
Show more (2)

Exploitation evidence

  1. Review command interpreters spawned by the affected service or application.Telemetry: DeviceProcessEvents · Unexpected process lineage can support command-injection hunting. · Rule command-injection

Response

  1. Recheck the affected assets after the source-stated mitigation or update is applied.Telemetry: DeviceTvmSoftwareVulnerabilities · A follow-up inventory check verifies local remediation. · Rule kev-network-exposure

CISA KEV Record

Catalog entry
23 Jun 2023
Required action due
14 Jul 2023
Known ransomware use
Unknown

Apply updates per vendor instructions.

Change History & Source Data

— No recorded material change

CNA / source
security@zyxel.com.tw
Record status · verification
UPDATED · CISA KEV confirmed
CPE
cpe:2.3:o:zyxel:nas326_firmware:*:*:*:*:*:*:*:*, cpe:2.3:h:zyxel:nas326:-:*:*:*:*:*:*:*, cpe:2.3:o:zyxel:nas540_firmware:*:*:*:*:*:*:*:*, cpe:2.3:h:zyxel:nas540:-:*:*:*:*:*:*:*, cpe:2.3:o:zyxel:nas542_firmware:*:*:*:*:*:*:*:*, cpe:2.3:h:zyxel:nas542:-:*:*:*:*:*:*:*

Evidence & Provenance

4 public sources
CISA KEV CatalogAdded 2023-06-23zyxel.comSource recordnvd.nist.govSource recordcisa.govSource record

Linked by the query's stored exact CVE association. Review required tables and validation status before use.

Detection Hunting Query
Target: DeviceTvmSoftwareVulnerabilities•Defender XDR
Detect endpoints exposed to CVE-2023-27992
Purpose: Exposure assessment (Category: Exposure Check)Why linked: Query metadata names CVE-2023-27992
DeviceTvmSoftwareVulnerabilities| where CveId == "CVE-2023-27992"| project DeviceId, DeviceName, OSPlatform, OSVersion, SoftwareVendor, SoftwareName, SoftwareVersion, CveId, VulnerabilitySeverityLevel, RecommendedSecurityUpdate, RecommendedSecurityUpdateId| sort by VulnerabilitySeverityLevel desc
Schema Checked · Not runtime validatedSource: SecOps Signal deterministic template · Limited verificationStatic screening: Passed structure and schema checks; tenant execution is not verified.
Open KQL Library

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Correlated briefings

SecOps Signal surfaces public advisory facts only. A missing value means the source has not published it, not that your environment is unaffected. No tenant inventory is connected.