CVE-2023-34140

What it is

A buffer overflow vulnerability in the Zyxel ATP series firmware versions 4.32 through 5.36 Patch 2, USG FLEX series firmware versions 4.50 through 5.36 Patch 2, USG FLEX 50(W) series firmware versions 4.16 through 5.36 Patch 2, USG20(W)-VPN series firmware versions 4.16 through 5.36 Patch 2, VPN series firmware versions 4.30 through 5.36 Patch 2, NXC2500 firmware versions 6.10(AAIG.0) through 6.10(AAIG.3), and NXC5500 firmware versions 6.10(AAOS.0) through 6.10(AAOS.4), could allow an unauthenticated, LAN-based attacker to cause denial of service (DoS) conditions by sending a crafted request to the CAPWAP daemon.

At a glance

Exploitability

Can be exploited from the same network segment without logging in. High risk of service disruption.

Exploit odds

0.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2023-07-17 18:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 06:02 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.3% in the next 30 days (EPSS).
• Severity: 6.5 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2023-07-17 18:15 UTC

Last modified

2026-06-17 06:02 UTC

Exploit probability

0.3% · EPSS, next 30 days

Weakness

CWE-120 · Classic buffer overflow

Record status

Modified

Affected

• Zyxel Usg 20w-vpn Firmware < 5.37
• Zyxel Usg 2200-vpn Firmware < 5.37
• Zyxel Usg Flex 100 Firmware < 5.37
• Zyxel Usg Flex 100w Firmware < 5.37
• Zyxel Usg Flex 200 Firmware < 5.37
• Zyxel Usg Flex 50 Firmware < 5.37
• Zyxel Usg Flex 500 Firmware < 5.37
• Zyxel Usg Flex 50w Firmware < 5.37

Attack profile CVSS 3.1 · 6.5

Attack vector

Adjacent network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

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Read https://cve-list.com/agent/cve/CVE-2023-34140.md and follow it. Check whether this project is affected by CVE-2023-34140. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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