CVE-2026-3871

Temporary UPnP interruption via DeletePortMapping buffer overflow

Published Jun 2, 2026 · Updated Jun 2, 2026

Buffer overflow in Zyxel VMG4005-B50B firmware 5.13(ABRL.5.4)C0 and earlier allows adjacent attackers to interrupt UPnP. The DeletePortMapping command mishandles an unspecified field in a crafted UPnP request; Zyxel has not disclosed the affected buffer or copy operation. Exploitation requires LAN/WLAN access and interrupts only the UPnP function temporarily, while ordinary network traffic continues.

CVSS severity6.5
Medium
EPSS probability0.17%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer overflow in Zyxel VMG4005-B50B firmware 5.13(ABRL.5.4)C0 and earlier allows adjacent attackers to interrupt UPnP. The DeletePortMapping command mishandles an unspecified field in a crafted UPnP request; Zyxel has not disclosed the affected buffer or copy operation. Exploitation requires LAN/WLAN access and interrupts only the UPnP function temporarily, while ordinary network traffic continues.

The record

CVE
CVE-2026-3871
Published
Jun 2, 2026
Updated
Jun 2, 2026
Vendor
Zyxel Networks
Product
VMG4005-B50B Firmware
Classifications
CWE-120, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 2, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 2, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 5.13(ABRL.5.4)C0

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Zyxel Networks · VMG4005-B50B Firmwareversion=<= 5.13(ABRL.5.4)C0

Published CVSS scores

6.5Zyxel CorporationCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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