No exploitation reportedFix available

CVE-2023-27991

Q: Is CVE-2023-27991 actively exploited?

Active exploitation of CVE-2023-27991 has not been confirmed. Its EPSS score was 1.5% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2023-27991?

CVE-2023-27991 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

No exploitation reported by the sources we read.

Published2023-04-24
Fixed in5.36
WeaknessCWE-78

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

The post-authentication command injection vulnerability in the CLI command of Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.16 through 5.35, USG20(W)-VPN firmware versions 4.16 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow an authenticated attacker to execute some OS commands remotely.

Timeline

dates in UTC

2023-04-2418:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2023-27991?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2023-27991?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Zyxel atp100 firmwareversion to verify

Branch	Affected	Fixed in	Source
5.36	≥ 4.32, < 5.36	5.36	NVD

Zyxel atp100w firmwareversion to verify

Branch	Affected	Fixed in	Source
5.36	≥ 4.32, < 5.36	5.36	NVD

Zyxel atp200 firmwareversion to verify

Branch	Affected	Fixed in	Source
5.36	≥ 4.32, < 5.36	5.36	NVD

16 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Zyxel atp100 firmware to 5.36

Advisories and patches

www.zyxel.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionnone2025-02-04
OpenCVESSVC decisionnone—
CNACVSS 3.18.8read 2026-10-23
NVDCVSS 3.18.8read 2026-10-23
CNAweakness (CWE)CWE-78read 2026-10-23
NVDweakness (CWE)CWE-78read 2026-10-23
FIRST EPSSEPSS score1.5 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Published: 2023-04-24
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2023-27991?

Is CVE-2023-27991 actively exploited?

Active exploitation of CVE-2023-27991 has not been confirmed. Its EPSS score was 1.5% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2023-27991?

CVE-2023-27991 has a CVSS v3 base score of 8.8 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

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