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Ax7501 B0 FirmwareOperating system · Zyxel

CVE-2021-35036

MEDIUM · 6.5 CVSS v3.1 Published 2022-03-01
Fix available
A fix is available. Upgrade to 5.17 / 5.40 or later.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

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
A cleartext storage of information vulnerability in the Zyxel VMG3625-T50B firmware version V5.50(ABTL.0)b2k could allow an authenticated attacker to obtain sensitive information from the configuration file.

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

The Zyxel VMG3625-T50B router firmware stores sensitive information in cleartext within its configuration file. An authenticated attacker with access to the device or its configuration backup can read the stored credentials or other sensitive data directly from the unencrypted configuration file.

MitigationApply vendor firmware update when available. Until then, restrict administrative access to the device to trusted personnel only and protect configuration file backups from unauthorized 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
Ax7501 B0 FirmwareOperating system
Affected:< 5.17\(abpc.2\)c0
Dx3301 T0 FirmwareOperating system
Affected:< 5.50\(abvy.3\)c0
Dx5401 B0 FirmwareOperating system
Affected:< 5.17\(abyo.2\)c0
Emg3525 T50b FirmwareOperating system
Affected:< 5.50\(abpm.7\)c0
Emg5523 T50b FirmwareOperating system
Affected:< 5.50\(abpm.7\)c0
Emg5723 T50k FirmwareOperating system
Affected:< 5.50\(abom.8\)c0
Ep240p FirmwareOperating system
Affected:< 5.40\(abvh.0\)c0a03
Ex5401 B0 FirmwareOperating system
Affected:< 5.17\(abyo.2\)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
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

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 your device model
    Check the device label or web interface to confirm the exact model number (e.g., VMG3625-T50B, EMG5523-T50b, etc.)
    Affected if Device model matches one of: Ax7501 B0, Dx3301 T0, Dx5401 B0, Emg3525 T50b, Emg5523 T50b, Emg5723 T50k, Ep240p, Ex5401 B0
  2. Check the installed firmware version
    Access the router web administration interface or use the device CLI to locate the firmware version information; compare it against the affected version thresholds
    Affected if Firmware version is below the fixed release for your model: Ax7501 B0 < 5.17(abpc.2)c0, Dx3301 T0 < 5.50(abvy.3)c0, Dx5401 B0 < 5.17(abyo.2)c0, Emg3525 T50b < 5.50(abpm.7)c0, Emg5523 T50b < 5.50(abpm.7)c0, Emg5723 T50k < 5.50(abom.8)c0, Ep240p < 5.40(abvh.0)c0a03, Ex5401 B0 < 5.17(abyo.2)c0
  3. Examine the configuration backup file
    If available, obtain a configuration backup or access the configuration file directly on the device; search for stored credentials or sensitive data that appears in plain text rather than obfuscated or encrypted
    Affected if Configuration file contains username/password pairs or other sensitive information in readable plaintext format

You are affected if your device is one of the listed models and running a firmware version lower than the fixed release, AND your configuration file contains unencrypted sensitive data.

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 5.17 / 5.40 / 5.50 or later
Fixed in 5.175.405.50
Interim mitigation

Apply vendor firmware update when available. Until then, restrict administrative access to the device to trusted personnel only and protect configuration file backups from unauthorized access.

Recommended fix High confidence

Upgrade to firmware version 5.17(abpc.2)c0 or later for Ax7501 B0; 5.50(abvy.3)c0 or later for Dx3301 T0; 5.17(abyo.2)c0 or later for Dx5401 B0/Ex5401 B0; 5.50(abpm.7)c0 or later for Emg3525 T50b/Emg5523 T50b; 5.50(abom.8)c0 or later for Emg5723 T50k; 5.40(abvh.0)c0a03 or later for Ep240p

  1. 1. Identify the specific Zyxel device model from the affected product list (Ax7501 B0, Dx3301 T0, Dx5401 B0, Emg3525 T50b, Emg5523 T50b, Emg5723 T50k, Ep240p, or Ex5401 B0)
  2. 2. Determine the current firmware version by accessing the device's web interface or administrative console
  3. 3. Navigate to the firmware update or administration section of the device
  4. 4. Download the appropriate fixed firmware version from Zyxel's official support website (www.zyxel.com) for your specific device model
  5. 5. Upload and apply the firmware update following Zyxel's standard firmware upgrade procedure
  6. 6. After the firmware update completes, verify the new version matches or exceeds the fixed version for your device
  7. 7. Confirm the vulnerability is resolved by checking that sensitive configuration data is no longer stored in cleartext
Caveat Firmware upgrades may temporarily disrupt network connectivity; ensure appropriate maintenance window and backup configuration before upgrading

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

Fix this in Ax7501 B0 Firmware Scoped from the published advisory
  • Consultation8.0 h
  • Implementation4.0 h
  • Testing4.0 h
  • Review / QA4.0 h
20.0 hours of engineering $3,640
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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-2021-35036 in production — separate from our analysis above.

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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
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  • No spam, self-promotion, credentials, or personal data