What is CVE-2026-3870?

CVE-2026-3870 is a medium-severity vulnerability in Zyxel Vmg4005-b50b Firmware, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 6.5/10. Published 2026-06-02.

How severe is CVE-2026-3870?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Buffer overflow in Zyxel Vmg4005-b50b Firmware

CVE-2026-3870

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 U…

Vulnerability class: Buffer Overflow

EPSS: 0.000 (3.6th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

Affected products

Zyxel Vmg4005-b50b Firmware — versions <= 5.13(ABRL.5.4)C0

Weakness classification (CWE)

CWE-120 — Buffer Copy without Checking Size of Input (Classic Buffer Overflow)

References

security@zyxel.com.tw (vendor-advisory)

Frequently asked questions

What is CVE-2026-3870?: CVE-2026-3870 is a medium-severity vulnerability in Zyxel Vmg4005-b50b Firmware, classified under Buffer Copy without Checking Size of Input (Classic Buffer Overflow). CVSS score: 6.5/10. Published 2026-06-02.
How severe is CVE-2026-3870?: Medium severity. CVSS v3 base score is 6.5 out of 10.