How severe is CVE-2023-6399?

CVE-2023-6399 has a CVSS 3.x base score of 5.7, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2023-6399 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2023-6399?

CVE-2023-6399 primarily affects Zyxel Atp100 Firmware. In total, 65 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-6399?

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

Does CVE-2023-6399 have an EU (EUVD) identifier?

Yes. CVE-2023-6399 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2023-58636.

When was CVE-2023-6399 published?

CVE-2023-6399 was published on 2024-02-20 and last updated on 2026-06-17.

CVE-2023-6399

CVE-2023-6399 is a medium-severity vulnerability in Zyxel Atp100 Firmware with a CVSS 3.x base score of 5.7. 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-134.

Key facts

Severity: Medium (CVSS 3.x base score 5.7)
EPSS exploit prediction: 1% (47th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2023-58636
Weakness: CWE-134
Affected product: Zyxel Atp100 Firmware
Published: 2024-02-20
Last modified: 2026-06-17

Description

A format string vulnerability in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4.50 through 5.37 Patch 1, USG FLEX 50(W) series firmware versions from 4.16 through 5.37 Patch 1, USG20(W)-VPN series firmware versions from 4.16 through 5.37 Patch 1, and USG FLEX H series firmware versions from 1.10 through 1.10 Patch 1 could allow an authenticated IPSec VPN user to cause DoS conditions against the “deviceid” daemon by sending a crafted hostname to an affected device if it has the “Device Insight” feature enabled.

Frequently asked questions

What is CVE-2023-6399?: A format string vulnerability in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4.50 through 5.37 Patch 1, USG FLEX 50(W) series firmware versions from 4.16 through 5.37 Patch 1, USG20(W)-VPN series firmware versions from 4.16 through 5.37 Patch 1, and USG FLEX H series firmware versions from 1.10 through 1.10 Patch 1 could allow an authenticated IPSec VPN user to cause DoS conditions against the “deviceid” daemon by sending a crafted hostname to an affected device if it has the “Device Insight” feature enabled.
How severe is CVE-2023-6399?: CVE-2023-6399 has a CVSS 3.x base score of 5.7, rated medium severity. It is exploitable over an adjacent network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2023-6399 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (47th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2023-6399?: CVE-2023-6399 primarily affects Zyxel Atp100 Firmware. In total, 65 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2023-6399?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2023-6399 have an EU (EUVD) identifier?: Yes. CVE-2023-6399 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2023-58636.
When was CVE-2023-6399 published?: CVE-2023-6399 was published on 2024-02-20 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-aps-02-20-2024

Affected products (65)

cpe:2.3:o:zyxel:atp100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100ax_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100ax_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100ax_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100h_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100h_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100h_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100w_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_100w_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200h_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200h_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200h_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200hp_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200hp_firmware:5.37:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_200hp_firmware:5.37:patch1:*:*:*:*:*:*
cpe:2.3:o:zyxel:usg_flex_500_firmware:*:*:*:*:*:*:*:*

More vulnerabilities in Zyxel Atp100 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-2023-28771 — Critical (CVSS 9.8): Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware…
CVE-2022-30525 — Critical (CVSS 9.8): A OS command injection vulnerability in the CGI program of Zyxel USG FLEX 100(W) firmware versions 5.00 through 5.21…
CVE-2022-0342 — Critical (CVSS 9.8): An authentication bypass vulnerability in the CGI program of Zyxel USG/ZyWALL series firmware versions 4.20 through…
CVE-2020-29583 — Critical (CVSS 9.8): Firmware version 4.60 of Zyxel USG devices contains an undocumented account (zyfwp) with an unchangeable password. The…

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Other CWE-134 vulnerabilities

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CVE-2011-2475 — Critical (CVSS 10.0): Format string vulnerability in ECTrace.dll in the iMailGateway service in the Internet Mail Gateway in OneBridge Server…
CVE-2011-1568 — Critical (CVSS 10.0): Format string vulnerability in the logText function in shmemmgr9.dll in IGSSdataServer.exe 9.00.00.11074, and…
CVE-2010-4235 — Critical (CVSS 10.0): Format string vulnerability in RealNetworks Helix Server 12.x, 13.x, and 14.x before 14.2, and Helix Mobile Server…
CVE-2011-0270 — Critical (CVSS 10.0): Format string vulnerability in nnmRptConfig.exe in HP OpenView Network Node Manager (OV NNM) 7.51 and 7.53 allows…

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