CVE-2026-36603

Unauthenticated port forwarding via exposed UPnP actions

Published Jun 3, 2026 · Updated Jun 3, 2026

Missing authentication in Mercusys AC12G (EU) V1 firmware allows remote attackers on the LAN to invoke UPnP IGD actions. The IGD SOAP handler on port 1900 in firmware AC12G(EU)_V1_200909 and AC12G(EU)_V1_210128 exposes 15 of 18 actions without authentication or per-action approval. LAN access is sufficient to create or delete NAT forwarding rules, disconnect the WAN, and read the WAN address and traffic statistics.

CVSS severity8.1
High
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Missing authentication in Mercusys AC12G (EU) V1 firmware allows remote attackers on the LAN to invoke UPnP IGD actions. The IGD SOAP handler on port 1900 in firmware AC12G(EU)_V1_200909 and AC12G(EU)_V1_210128 exposes 15 of 18 actions without authentication or per-action approval. LAN access is sufficient to create or delete NAT forwarding rules, disconnect the WAN, and read the WAN address and traffic statistics.

The record

CVE
CVE-2026-36603
Published
Jun 3, 2026
Updated
Jun 3, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-306, T1562.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

8.1CISA-ADPCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-306Missing Authentication for Critical Function
T1562.004Disable or Modify System Firewall

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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