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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 14 Jul 2023.
Nas326 FirmwareOperating system · Zyxel

CVE-2023-27992

CRITICAL · 9.8 CVSS v3.1 Published 2023-06-19
Fix available
A fix is available. Upgrade to 5.21 or later.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Zyxel NAS326, NAS540, and NAS542 devices contain a pre-authentication command injection vulnerability in their web interface. Attackers can send crafted HTTP requests to execute arbitrary OS commands without any authentication, gaining full control of the device.

MitigationApply vendor-supplied firmware updates (NAS326: V5.21(AAZF.14)C0, NAS540: V5.21(AATB.11)C0, NAS542: V5.21(ABAG.11)C0 or later) to all affected devices. If patching is not immediately possible, restrict network access to the management interface via firewall rules or disable remote access.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Nas326 FirmwareOperating system
Affected:< 5.21\(aazf.14\)c0
Nas540 FirmwareOperating system
Affected:< 5.21\(aatb.11\)c0
Nas542 FirmwareOperating system
Affected:< 5.21\(abag.11\)c0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the NAS device model
    Access the device web management interface or check the device label to confirm the model is NAS326, NAS540, or NAS542
    Affected if The device is one of these three models
  2. Check the installed firmware version
    Log into the web management interface and navigate to System > Firmware or check the version displayed on the dashboard. Compare the version number against the affected ranges: NAS326 < 5.21(aazf.14)c0, NAS540 < 5.21(aatb.11)c0, NAS542 < 5.21(abag.11)c0
    Affected if The firmware version is lower than the patched version for your model
  3. Verify HTTP management interface accessibility
    Attempt to access the device web interface over HTTP/HTTPS from the network
    Affected if The management interface is reachable from an untrusted network (this is the attack vector)
  4. Review web server logs for suspicious requests
    Check the device system logs or web server access logs for unusual or malformed HTTP requests, especially those containing shell metacharacters or unexpected parameter values
    Affected if Logs show crafted HTTP requests with command injection patterns

A device is affected if it is a NAS326, NAS540, or NAS542 running firmware versions below 5.21(aazf.14)c0, 5.21(aatb.11)c0, or 5.21(abag.11)c0 respectively, and its HTTP management interface is accessible to attackers.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 5.21 or later
Fixed in 5.21
Vendor patch www.zyxel.com →
Interim mitigation

Apply vendor-supplied firmware updates (NAS326: V5.21(AAZF.14)C0, NAS540: V5.21(AATB.11)C0, NAS542: V5.21(ABAG.11)C0 or later) to all affected devices. If patching is not immediately possible, restrict network access to the management interface via firewall rules or disable remote access.

Recommended fix High confidence

Nas326: V5.21(AAZF.14)C0 | Nas540: V5.21(AATB.11)C0 | Nas542: V5.21(ABAG.11)C0

  1. Identify your specific NAS model (Nas326, Nas540, or Nas542)
  2. Access the Zyxel device web management interface
  3. Navigate to Administration > Firmware upgrade section
  4. Download the appropriate firmware version: Nas326 to V5.21(AAZF.14)C0, Nas540 to V5.21(AATB.11)C0, or Nas542 to V5.21(ABAG.11)C0 from the official Zyxel support website
  5. Upload the firmware file and initiate the upgrade process
  6. Wait for the device to reboot and verify the firmware version has been updated

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Nas326 Firmware Exploited in the wild — priority engagement
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,088.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-27992 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data