Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2023-28771

ZyWALL/USG series firmware

Zyxel / ZyWALL/USG series firmware · 4.60 through 4.73

Watch CVE-2023-28771 Browse KEV feed
Severity
CVSS 9.8 · Critical
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
99.3%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2023-28771 is an unauthenticated vulnerability affecting Zyxel ZyWALL/USG series firmware and 3 other products. Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN...

Is it exploited?

Yes. Previdian tracks this CVE as a known exploited vulnerability. Confidence is confirmed. Listed in CISA KEV. Also confirmed by third-party sources.

Who is affected?

Zyxel / ZyWALL/USG series firmware 4.60 through 4.73.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

ZyWALL/USG series firmware

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.

Zyxel Affected
ZyWALL/USG series firmware
4.60 through 4.73
Zyxel Affected
VPN series firmware
4.60 through 5.35
Zyxel Affected
USG FLEX series firmware
4.60 through 5.35
Zyxel Affected
ATP series firmware
4.60 through 5.35
Published
25 Apr 2023
Exploitation Reported
31 May 2023
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

cisa edge metasploit

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 31 May 2023

A trusted third party reported exploitation.

Proof of concept available

GitHub

Recorded 23 May 2023

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

Learn about Pro API access
Source Added
CISA First 2023-05-31 00:00 UTC
The Shadowserver 2026-05-27 00:00 UTC
Daily CyberSecurity 2026-06-18 01:20 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Virtual patch status

No Previdian virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Metasploit https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/linux/misc/zyxel_ike_decoder_rce_cve_2023_28771.rb 28 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

9.8 Critical

Potential damage if exploited. Separate from whether attackers are using it.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS

99.3%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') CWE-78

Recent mention · Daily CyberSecurity

Zyxel Patches Stack-Based Buffer Overflow in GS1900 Switches (CVE-2026-7273)

Zyxel has rolled out firmware patches for a serious flaw in its popular GS1900 series switches. Tracked as The post Zyxel Patches Stack-Based Buffer Overflow in GS1900 Switches (CVE-2026-7273) appeared first on Daily CyberSecurity. Related posts: Zyxel Firewalls Under Attack...

Read full advisory

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

zyxel_ike_decoder_rce_cve_2023_28771

metasploit · Created Unknown

Metasploit module for CVE-2023-28771

Timeline

From disclosure to observed exploitation

  1. 01:20 UTC

    KEV confirmed by Daily CyberSecurity

    Exploitation attested by an external source

  2. 00:00 UTC

    KEV confirmed by The Shadowserver

    Exploitation attested by an external source

  3. 15:02 UTC

    Metasploit module available

    Exploit module available

  4. 15:02 UTC

    Public PoC available

    Public proof-of-concept code published

  5. 00:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  6. 00:00 UTC

    CVE published

    Vulnerability disclosed publicly

  7. 00:00 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

Start 14-day Pro trial Read API docs
  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2023-28771

Sample API response 
{
  "cve_id": "CVE-2023-28771",
  "confidence": "Confirmed",
  "cvss_score": 9.8,
  "cvss_estimated": false,
  "epss_score": 0.99284,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}