How severe is CVE-2026-3871?

CVE-2026-3871 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2026-3871 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-3871?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-3871 have an EU (EUVD) identifier?

Yes. CVE-2026-3871 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-33876.

When was CVE-2026-3871 published?

CVE-2026-3871 was published on 2026-06-02 and last updated on 2026-06-17.

CVE-2026-3871

CVE-2026-3871 is a medium-severity vulnerability with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-120.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (6th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-33876
Weakness: CWE-120
Published: 2026-06-02
Last modified: 2026-06-17

Description

A buffer overflow vulnerability in the UPnP DeletePortMapping() 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.

Frequently asked questions

What is CVE-2026-3871?: A buffer overflow vulnerability in the UPnP DeletePortMapping() 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.
How severe is CVE-2026-3871?: CVE-2026-3871 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2026-3871 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (6th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-3871?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-3871 have an EU (EUVD) identifier?: Yes. CVE-2026-3871 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-33876.
When was CVE-2026-3871 published?: CVE-2026-3871 was published on 2026-06-02 and last updated on 2026-06-17.

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

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