© 2026 vulntracker.io

CVE-2023-27991

HIGH

8.8

CVSS Score

Published: April 24, 2023 at 12:00 AM UTC

Updated: June 17, 2026 at 05:46 AM UTC

42 products affected across 1 vendorUsg Flex 100W FirmwareUSG FLEX 200 firmwareUSG FLEX 700 firmware

Using ATP series firmware by Zyxel?

Get instant alerts when new vulnerabilities affect ATP series firmware - before attackers find them.

Real-time alertsTrack your software stackFree plan available

Start Free Sign In

Severity

HIGH8.8

Exploit prediction

EPSS 1%

SSVC

No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

ATP100 Firmware · Zyxel

95%

4.32 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

ATP100W Firmware · Zyxel

95%

4.32 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-atp100w (same device)

ATP200 Firmware · Zyxel

95%

4.32 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-atp200 (same device)

ATP500 Firmware · Zyxel

95%

4.32 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-atp500 (same device)

ATP700 Firmware · Zyxel

95%

4.32 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-atp700 (same device)

ATP800 Firmware · Zyxel

95%

4.32 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-atp800 (same device)

Usg 20W VPN Firmware · Zyxel

95%

4.16 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

Usg Flex 100 Firmware · Zyxel

95%

4.50 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-usg-flex-100 (same device)

Usg Flex 100W Firmware · Zyxel

95%

4.50 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-usg-flex-100w (same device)

USG FLEX 200 firmware · Zyxel

95%

4.50 ≤ v < 5.36

Affected range stops below 5.36, so it looks safe — our inference, not a vendor statement

zyxel-usg-flex-200 (same device)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-xss-vulnerability-and-post-authentication-command-injection-vulnerability-in-firewalls

References (1)

Vendor Advisory

Source: [email protected]

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-xss-vulnerability-and-post-authentication-command-injection-vulnerability-in-firewalls

SSVC — Action Prioritization

SSVCNo known exploitNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

8.8HIGHZyxel

Attack Vector: NETWORK
Complexity: LOW
Privileges: LOW
User Interaction: NONE
Scope: UNCHANGED
Confidentiality: HIGH
Integrity: HIGH
Availability: HIGH

Vector?

Quick Info

StatusMODIFIED

CWE

CWE-78

Get alerted

Stop reading CVE feeds looking for your own stack

Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.

Create account Sign in

Free plan, no card