Vulnerability · Published Jun 2, 2026 · Assigned by Zyxel

CVE-2026-3870

Medium 6.5

In plain English

A medium-severity buffer overflow in VMG4005-B50B firmware from Zyxel. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 6% of all known vulnerabilities).

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.2%top 93.8% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

A buffer overflow vulnerability in the UPnP AddPortMapping() command in Zyxel VMG4005-B50B firmware versions through 5.13(ABRL.5.4)C0 could allow an adjacent attacker to trigger a temporary denial-of-service (DoS) condition affecting the UPnP function of the affected device.

Affected products (as reported)

Vendor	Product	Versions
Zyxel	VMG4005-B50B firmware	<= 5.13(ABRL.5.4)C0

Weakness: CWE-120 · Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-buffer-overflow-vulnerabilities-in-the-upnp-function-of-certain-4g-lte-5g-nr-cpe-and-dsl-ethernet-cpe-06-02-2026 vendor-advisory