Is CVE-2026-36603 in the CISA KEV catalog?

No. CVE-2026-36603 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2026-36603?

CVE-2026-36603 has a CVSS v3 base score of 8.1 (HIGH).

What is the EPSS score for CVE-2026-36603?

CVE-2026-36603 has an EPSS score of 0.21% (11th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix or mitigate CVE-2026-36603?

No published fix for CVE-2026-36603 has been found yet. Check the linked vendor advisories for guidance as it becomes available.

CVE & CISA-KEV Catalog

CVE-2026-36603

HIGH

8.1

CVSS v3

NVD

Description

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.

CWE-306Missing Authentication for Critical Function

How to fix

No published remediation has been found for this vulnerability's affected products yet.

Mitigation guidance may be in the linked vendor advisories in the References section below.

CVSS v3 Vector

Exploitability

Attack VectorAdjacent

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

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

Exploit Intelligence

0.21%probability of exploitation in 30 days

11thpercentile

Low risk: more likely to be exploited than 11% of all known CVEs.

References

Other references1

github.com

Related Vulnerabilities

Other CWE-306 (Missing Authentication for Critical Function) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2017-10271	High	7.5	100%	KEV + Ransom	-
CVE-2023-42793	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2025-3248	Critical	9.8	100%	KEV	Fix
CVE-2022-1388	Critical	9.8	100%	KEV + Ransom	Fix
CVE-2021-37415	Critical	9.8	100%	KEV	-
CVE-2023-21839	High	7.5	100%	KEV	-

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-05.