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Missing AuthenticationWeakness · CWE-306

CVE-2026-36603

HIGH · 8.1 CVSS v3.1 Published 2026-06-03
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
86/100
Remediation priority · High
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
Mercusys AC12G (EU) V1 router with firmware AC12G(EU)_V1_200909 exposes 15 of 18 UPnP IGD actions without authentication on port 1900, including AddPortMapping and GetExternalIPAddress. UPnP is enabled by default through the admin interface, allowing any unauthenticated LAN device to create arbitrary port forwarding rules and access WAN traffic statistics.

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 Mercusys AC12G router firmware has an improper access control vulnerability in its UPnP IGD service running on port 1900. The UPnP implementation exposes 15 of 18 available actions—including AddPortMapping and GetExternalIPAddress—without any authentication, allowing any LAN device to manipulate port forwarding rules and access WAN traffic statistics.

MitigationDisable UPnP through the router's admin interface; if UPnP functionality is required, check for firmware updates or evaluate replacing the device with a model that properly authenticates UPnP requests.

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

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
Adjacent
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 the router model
    Access the router's admin interface (typically at 192.168.0.1 or 192.168.1.1) and check the device information page to confirm the model is Mercusys AC12G. Alternatively, check the device label on the router hardware itself.
    Affected if The device is a Mercusys AC12G router.
  2. Verify UPnP is enabled on the router
    Log into the router's administrative interface, navigate to the Advanced or Forwarding settings, and locate the UPnP setting. Check whether it is turned ON or OFF.
    Affected if UPnP is enabled (ON) on the router - this is required for the vulnerability to be exploitable.
  3. Confirm port 1900 is accessible from the local network
    From a device on the same local network, run a port scan or simple connectivity check: nc -zv <router-ip> 1900 or telnet <router-ip> 1900. A response indicates the port is open.
    Affected if Port 1900 on the router responds to requests from the LAN, meaning the UPnP service is network-accessible.
  4. Test UPnP IGD authentication requirement
    Send a SOAP request to the router's UPnP endpoint (typically http://<router-ip>:1900/igdctlg/ctl/IA_WANIPConn1 or /ctl/IGD_ctl) with an action like GetExternalIPAddress. Use a tool like curl: curl -X POST -H 'SOAPACTION: "urn:schemas-upnp-org:service:WANIPConnection:1#GetExternalIPAddress"' -d '<?xml version="1.0"?><s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/" s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/"><s:Body><u:GetExternalIPAddress xmlns:u="urn:schemas-upnp-org:service:WANIPConnection:1"></u:GetExternalIPAddress></s:Body></s:Envelope>' http://<router-ip>:19
    Affected if The router responds with WAN IP information or accepts the request without requiring any authentication credentials - the device is vulnerable.
  5. Confirm AddPortMapping action is available
    Send a SOAP AddPortMapping request to the same UPnP endpoint with arbitrary mapping parameters. If the router accepts and creates the mapping without authentication, the vulnerability is confirmed.
    Affected if The AddPortMapping action executes successfully without authentication, allowing attackers to create arbitrary port forwarding rules.

If you have a Mercusys AC12G router with UPnP enabled and port 1900 responds to unauthenticated SOAP requests from the LAN, your router is affected by this vulnerability.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Disable UPnP through the router's admin interface; if UPnP functionality is required, check for firmware updates or evaluate replacing the device with a model that properly authenticates UPnP requests.

Have this fixed Scoped from the published advisory
  • Consultation1.0 h
  • Implementation0.5 h
  • Testing1.0 h
  • Review / QA0.5 h
3.0 hours of engineering $750
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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-2026-36603 in production — separate from our analysis above.

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What belongs here
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