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Weekly Signal
Live intelligence Updated 19 Aug 2026 · 13:41 UTC

Zyxel · Atp100 Firmware, Atp100w Firmware, Atp200 Firmware +17 more

CVE-2023-28771

Zyxel Multiple Firewalls OS Command Injection Vulnerability

Recommended action

Treat this as an immediate remediation priority. Apply updates per vendor instructions.

View response plan
CVSS9.8
EPSS99.3%
KEVYes
ExploitationConfirmed exploitation
PatchPatch or guidance available ↓

Assessment

Why it matters

CISA lists this vulnerability as known to be exploited; exploitation is confirmed; EPSS is 99.3%; technical severity is CVSS 9.8.

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.

Who should care

  • Teams operating Atp100 Firmware, Atp100w Firmware, Atp200 Firmware +17 more
  • Vulnerability and exposure management teams
  • Security operations teams monitoring exploitation activity

Response plan

What I would do

  1. Confirm whether Atp100 Firmware, Atp100w Firmware, Atp200 Firmware +17 more is present in the environment.
  2. Identify affected versions and establish whether vulnerable services are exposed or reachable.
  3. Apply updates per vendor instructions.
  4. Review relevant security telemetry for evidence of attempted or successful exploitation.
  5. Document the remediation decision and track it to verified completion.

Vendor remediation

Patch and remediation links

Use the vendor source below to confirm the correct fixed version, package or mitigation for your affected product.

Technical details

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-78
Affected versions
Zyxel Atp100 Firmware (Start Including: 4.60, End Excluding: 5.36); Zyxel Atp100w Firmware (Start Including: 4.60, End Excluding: 5.35); Zyxel Atp200 Firmware (Start Including: 4.60, End Excluding: 5.36); Zyxel Atp500 Firmware (Start Including: 4.60, End Excluding: 5.36); Zyxel Atp700 Firmware (Start Including: 4.60, End Excluding: 5.36); Zyxel Atp800 Firmware (Start Including: 4.60, End Excluding: 5.36); Zyxel Multiple Firewalls; Zyxel Usg Flex 100 Firmware (Start Including: 4.60, End Excluding: 5.36)
Published
25 April 2023
Attack vector
Network
Privileges required
None
User interaction
None

Signal timeline

  1. CVE published
  2. Added to CISA KEV
  3. Latest EPSS score: 99.3%
  4. Signal calculated at 85

External references

Live public intelligence This assessment combines public-source evidence. Validate the affected product, version and exposure against your own environment before making a risk decision.