How severe is CVE-2023-28771?

CVE-2023-28771 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2023-28771 being actively exploited?

Yes. CVE-2023-28771 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2023-05-31, which means active exploitation has been confirmed. It should be prioritised for remediation.

What products are affected by CVE-2023-28771?

CVE-2023-28771 primarily affects Zyxel Atp100 Firmware. In total, 21 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2023-28771?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.

Does CVE-2023-28771 have an EU (EUVD) identifier?

Yes. CVE-2023-28771 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2023-32406. It is also flagged as exploited in the EUVD (since 2023-05-31).

When was CVE-2023-28771 published?

CVE-2023-28771 was published on 2023-04-25 and last updated on 2026-06-17.

CVE-2023-28771

CVE-2023-28771 is a critical-severity vulnerability in Zyxel Atp100 Firmware with a CVSS 3.x base score of 9.8. It is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming it has been exploited in the wild (added 2023-05-31). The underlying weakness is classified as CWE-78.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
EPSS exploit prediction: 99% (100th percentile)
Actively exploited: Yes — listed in CISA KEV (added 2023-05-31)
EU (EUVD) id: EUVD-2023-32406
EU exploitation: Flagged exploited in the ENISA EU Vulnerability Database (since 2023-05-31)
Weakness: CWE-78
Affected product: Zyxel Atp100 Firmware
Published: 2023-04-25
Last modified: 2026-06-17

Description

Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.

Frequently asked questions

What is CVE-2023-28771?: Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to an affected device.
How severe is CVE-2023-28771?: CVE-2023-28771 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2023-28771 being actively exploited?: Yes. CVE-2023-28771 is on CISA's Known Exploited Vulnerabilities (KEV) catalog, added on 2023-05-31, which means active exploitation has been confirmed. It should be prioritised for remediation.
What products are affected by CVE-2023-28771?: CVE-2023-28771 primarily affects Zyxel Atp100 Firmware. In total, 21 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2023-28771?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Because this CVE is known to be actively exploited, treat remediation as urgent — CISA KEV typically sets a short remediation deadline.
Does CVE-2023-28771 have an EU (EUVD) identifier?: Yes. CVE-2023-28771 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2023-32406. It is also flagged as exploited in the EUVD (since 2023-05-31).
When was CVE-2023-28771 published?: CVE-2023-28771 was published on 2023-04-25 and last updated on 2026-06-17.

References

Affected products (21)

cpe:2.3:o:zyxel:atp100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp100w_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp200_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp500_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp700_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:atp800_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:vpn100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn1000_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn300_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:vpn50_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_usg_310_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_usg_310_firmware:4.73:-:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_usg_100_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:zyxel:zywall_usg_100_firmware:4.73:-:*:*:*:*:*:*

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-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…
CVE-2020-9054 — Critical (CVSS 9.8): Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication…

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