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Nas326 FirmwareOperating system · Zyxel

CVE-2023-35137

HIGH · 7.5 CVSS v3.1 Published 2023-11-30
Fix available
A fix is available. Upgrade to after 5.21 or later.
See remediation →
84/100
Remediation priority · High
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
An improper authentication vulnerability in the authentication module of the Zyxel NAS326 firmware version V5.21(AAZF.14)C0 and NAS542 firmware version V5.21(ABAG.11)C0 could allow an unauthenticated attacker to obtain system information by sending a crafted URL to a vulnerable device.

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
How this class of weakness works · CWE-287

The mechanism that verifies who a user is can be side-stepped or fooled, letting an attacker act as someone they're not. Everything built on top of that identity then becomes untrustworthy. Fixing it means hardening the full authentication flow, including edge cases, tokens, and secondary paths.

General guidance for the improper authentication class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

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
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
None
Availability
None

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

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 a release after 5.21
Vendor patch www.zyxel.com →
Recommended fix Moderate confidence

Firmware version > V5.21(AAZF.14)C0 for NAS326 or > V5.21(ABAG.11)C0 for NAS542 (obtain exact latest version from Zyxel advisory)

  1. 1. Visit the Zyxel support portal at https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-authentication-bypass-and-command-injection-vulnerabilities-in-nas-products to obtain the latest firmware version for your device.
  2. 2. Identify your exact NAS model (NAS326 or NAS542).
  3. 3. Download the firmware version newer than V5.21(AAZF.14)C0 for NAS326 or newer than V5.21(ABAG.11)C0 for NAS542 from the official Zyxel support page.
  4. 4. Access the device web administration interface.
  5. 5. Navigate to the firmware upgrade section (typically under Administration > Firmware Upgrade).
  6. 6. Upload and apply the downloaded firmware file.
  7. 7. After the upgrade completes, verify the device is operational and confirm the new firmware version is installed.
  8. 8. Consider performing a factory reset after upgrade if the device remains unstable, though this may require reconfiguration.
Caveat Review Zyxel release notes for any configuration or feature changes between versions before upgrading

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

We can identify the exact fixed release, upgrade, and verify it in staging — typical engagement from $1,950. Get the upgrade done

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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-2023-35137 in production — separate from our analysis above.

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