How severe is CVE-2023-34140?

CVE-2023-34140 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-2023-34140 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (18th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-34140?

CVE-2023-34140 primarily affects Zyxel Usg 20w-vpn Firmware. In total, 24 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-34140?

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

When was CVE-2023-34140 published?

CVE-2023-34140 was published on 2023-07-17 and last updated on 2026-06-17.

CVE-2023-34140

CVE-2023-34140 is a medium-severity vulnerability in Zyxel Usg 20w-vpn Firmware 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% (18th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-120
Affected product: Zyxel Usg 20w-vpn Firmware
Published: 2023-07-17
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2023-34140?: 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.
How severe is CVE-2023-34140?: CVE-2023-34140 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-2023-34140 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (18th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-34140?: CVE-2023-34140 primarily affects Zyxel Usg 20w-vpn Firmware. In total, 24 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2023-34140?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2023-34140 published?: CVE-2023-34140 was published on 2023-07-17 and last updated on 2026-06-17.

References

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-wlan-controllers

Affected products (24)

cpe:2.3:o:zyxel:usg_20w-vpn_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_2200-vpn_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_50w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_atp100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_atp100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_atp200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_atp500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_atp700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_atp800_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn2s_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn_300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_vpn_50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:nxc2500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:nxc5500_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Zyxel Usg 20w-vpn Firmware

CVE-2023-33010 — Critical (CVSS 9.8): A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36…
CVE-2023-33009 — Critical (CVSS 9.8): A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36…
CVE-2023-33012 — High (CVSS 8.8): A command injection vulnerability in the configuration parser of the Zyxel ATP series firmware versions 5.10 through…
CVE-2023-33011 — High (CVSS 8.8): A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series…
CVE-2023-28767 — High (CVSS 8.8): The configuration parser fails to sanitize user-controlled input in the Zyxel ATP series firmware versions 5.10 through…
CVE-2023-27991 — High (CVSS 8.8): The post-authentication command injection vulnerability in the CLI command of Zyxel ATP series firmware versions 4.32…

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