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Emg3525 T50b FirmwareOperating system · Zyxel

CVE-2025-7673

CRITICAL · 9.8 CVSS v3.1 Published 2025-07-16
Fix available
A fix is available. Upgrade to 5.13 / 5.15 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges 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 buffer overflow vulnerability in the URL parser of the zhttpd web server in Zyxel VMG8825-T50K firmware versions prior to V5.50(ABOM.5)C0 could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and potentially execute arbitrary code by sending a specially 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

A buffer overflow vulnerability exists in the URL parser of the zhttpd web server in Zyxel VMG8825-T50K routers. An unauthenticated remote attacker can send a specially crafted HTTP request with an excessively long or malformed URL to overflow a buffer, potentially leading to denial of service or arbitrary code execution with elevated privileges.

MitigationUpgrade the Zyxel VMG8825-T50K firmware to version V5.50(ABOM.5)C0 or later to patch the vulnerability. If upgrades are not immediately possible, consider restricting external access to the web interface via firewall rules.

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
Emg3525 T50b FirmwareOperating system
Affected:< 5.50\(abpm.4\)c0< 5.50\(absl.0\)b8
Emg5523 T50b FirmwareOperating system
Affected:< 5.50\(abpm.4\)c0< 5.50\(absl.0\)b8
Emg5723 T50k FirmwareOperating system
Affected:< 5.50\(abom.5\)c0
Emg6726 B10a FirmwareOperating system
Affected:< 5.13\(abnp.6\).c
Ex3510 B0 FirmwareOperating system
Affected:< 5.17\(abup.3\)c0
Ex5510 B0 FirmwareOperating system
Affected:< 5.15\(abqx.3\)c0
Vmg1312 T20b FirmwareOperating system
Affected:< 5.50\(absb.3\)c0
Vmg3625 T50b FirmwareOperating system
Affected:< 5.50\(abpm.4\)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 Zyxel device model
    Check the device label or access the web admin interface (usually at 192.168.1.1) and look for the model number in the status or system information page
    Affected if The device model is NOT one of: EMG3525-T50b, EMG5523-T50b, EMG5723-T50k, EMG6726-B10a, Ex3510-B0, Ex5510-B0, VMG1312-T20b, or VMG3625-T50b (these are not affected)
  2. Check the installed firmware version
    In the web admin interface, go to Maintenance > Firmware Upgrade or System > Status to view the firmware version. Alternatively, access via CLI and run 'cat /etc/zyfw_version' or similar command
    Affected if The firmware version is below the fixed version for your specific model (see version ranges: EMG3525/5523-T50b < 5.50(abpm.4)c0 or < 5.50(absl.0)b8; EMG5723-T50k < 5.50(abom.5)c0; EMG6726-B10a < 5.13(abnp.6).c; Ex3510-B0 < 5.17(abup.3)c0; Ex5510-B0 < 5.15(abqx.3)c0; VMG1312-T20b < 5.50(absb.3)c0; VM
  3. Verify the zhttpd web server is enabled
    Check if the web interface is accessible by navigating to the device IP in a browser, or check via CLI for process: 'ps | grep zhttpd' or 'netstat -tlnp | grep http'
    Affected if The web interface is accessible and responds to HTTP/HTTPS requests (ports 80/443)
  4. Determine if external access to the web interface is permitted
    Check router firewall rules via CLI: 'iptables -L -n' or through the web interface under Security > Firewall. Look for rules allowing inbound traffic on ports 80/443 from external IPs
    Affected if Firewall rules allow inbound HTTP/HTTPS traffic from WAN/outside interfaces, meaning the web interface is exposed to the internet

You are affected if you have one of the listed Zyxel models, your firmware version is below the specified fixed versions, the zhttpd web server is running, and the web interface is accessible (especially from external networks).

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 5.13 / 5.15 / 5.17 or later
Fixed in 5.135.155.17
Interim mitigation

Upgrade the Zyxel VMG8825-T50K firmware to version V5.50(ABOM.5)C0 or later to patch the vulnerability. If upgrades are not immediately possible, consider restricting external access to the web interface via firewall rules.

Recommended fix Moderate confidence

V5.50(ABOM.5)C0 for VMG8825-T50K; latest available firmware for other affected models

  1. 1. Identify the exact model number of your Zyxel device from the affected product list.
  2. 2. Visit the official Zyxel support website (www.zyxel.com) and navigate to the firmware download section for your specific device model.
  3. 3. Download the latest firmware version available for your device. For VMG8825-T50K, ensure you obtain version V5.50(ABOM.5)C0 or later.
  4. 4. Access the device's web management interface via a browser.
  5. 5. Navigate to the Administration or Maintenance section, then locate the Firmware Upgrade or Update option.
  6. 6. Upload the downloaded firmware file and initiate the upgrade process.
  7. 7. Wait for the firmware upload and installation to complete - do not power off the device during this process.
  8. 8. After the device reboots, verify the firmware version has been updated successfully.
Caveat Firmware upgrades on embedded devices may reset some custom configurations; backup current settings before upgrading if possible

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

Fix this in Emg3525 T50b Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA6.0 h
30.0 hours of engineering $5,120
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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-2025-7673 in production — separate from our analysis above.

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