Cyber Resilience

CVE-2023-27992

RCE in Zyxel Nas326 Firmware ≤ 5.21\(aazf.14\)c0

CISA KEVActive ExploitationEUVD ExploitedRCECommand Injection
Published
19 June 2023
Modified
27 October 2025
KEV Added
23 June 2023
Patch / advisory
View advisory
CVSS Score v3.1 9.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.84 99.7th percentile
Risk Priority 97 floored blend · peak EPSS

Summary

CVE-2023-27992 is a critical-severity OS Command Injection (CWE-78) vulnerability in Zyxel Nas326 Firmware. Its CVSS base score is 9.8 (Critical).

Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked in the top 0.3% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2023-27992 is a pre-authentication command injection vulnerability (CWE-78) affecting Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0. The flaw resides in the handling of crafted HTTP requests that permit arbitrary operating system command execution without requiring authentication.

An unauthenticated remote attacker can exploit the issue over the network by sending a maliciously formatted HTTP request, achieving full control over the affected NAS device including the ability to read, modify, or delete data and execute arbitrary OS commands with high impact to confidentiality, integrity, and availability.

Zyxel’s security advisory directs customers to upgrade the listed NAS models to the specified patched firmware releases. The vulnerability is also catalogued in CISA’s Known Exploited Vulnerabilities list, confirming observed in-the-wild exploitation.

The associated EPSS score has reached a sustained high of 0.8653, indicating substantial exploitation interest following disclosure.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

The pre-authentication command injection vulnerability in the Zyxel NAS326 firmware versions prior to V5.21(AAZF.14)C0, NAS540 firmware versions prior to V5.21(AATB.11)C0, and NAS542 firmware versions prior to V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands remotely…

more

by sending a crafted HTTP request.

CWE(s)
CWE-78
KEV Date Added
23 June 2023

Related Threats

MITRE ATT&CK Enterprise Techniques

T1059 Command and Scripting Interpreter Execution
Adversaries may abuse command and script interpreters to execute commands, scripts, or binaries.
attack.mitre.org →
T1059.003 Windows Command Shell Execution
Adversaries may abuse the Windows command shell for execution.
attack.mitre.org →
T1059.004 Unix Shell Execution
Adversaries may abuse Unix shell commands and scripts for execution.
attack.mitre.org →
T1059.001 PowerShell Execution
Adversaries may abuse PowerShell commands and scripts for execution.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-27988Same product: Zyxel Nas326
CVE-2024-29972Same product: Zyxel Nas326
CVE-2024-6342Same product: Zyxel Nas326
CVE-2023-4473Same product: Zyxel Nas326
CVE-2023-37928Same product: Zyxel Nas326
CVE-2023-35138Same product: Zyxel Nas326
CVE-2024-29973Same product: Zyxel Nas326
CVE-2023-37927Same product: Zyxel Nas326
CVE-2023-5372Same product: Zyxel Nas326
CVE-2023-4474Same product: Zyxel Nas326

Affected Assets

zyxel
nas326 firmware
≤ 5.21\(aazf.14\)c0
zyxel
nas540 firmware
≤ 5.21\(aatb.11\)c0
zyxel
nas542 firmware
≤ 5.21\(abag.11\)c0

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V1.2.5
  • V1.2.8
  • V15.2.5

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

SC-27 Platform-independent Applications
addresses: CWE-78

Platform-independent apps typically execute inside a managed runtime or sandbox that restricts direct OS command execution, reducing the ability to exploit OS command injection.

SI-10 Information Input Validation
addresses: CWE-78

Validates inputs to block special elements that would alter OS command execution.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

PR.PS-06's SDLC practices directly require secure coding and input handling that blocks command-injection defects, yet the single broad outcome leaves many specific neutralization vectors and verification gaps unaddressed.

PR.PS-02 partial match
prevents

Routine patching/maintenance can remediate known command-injection CVEs in dependencies (partial forward) but does nothing to stop developers from introducing improper neutralization in custom code (none reverse).

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing and code review target insecure use of operating-system command interfaces, catching command-injection flaws introduced during development.

References