CVE-2023-4473NAS326 firmware OS Command Injection
A command injection vulnerability in the web server of the Zyxel NAS326 firmware version V5.21(AAZF.14)C0 and NAS542 firmware version V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands by sending a crafted URL to a vulnerable…
Published Dec 1, 2023 · Updated Dec 16, 2025
Key Facts
Patch immediately- CVE-2023-4473 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting NAS326 firmware (Zyxel), NAS542 firmware (Zyxel).
- It is exploited in the wild, listed in CIRCL KEV, Industry KEV feed since Apr 28, 2024. A public exploit is reported by tracking sources, but no code link is listed yet.
- EPSS estimates a 41% probability of exploitation in the next 30 days.
- Fixed versions are available, including NAS326 firmware <=5.21\(aazf.14\)c0, NAS542 firmware <=5.21\(abag.11\)c0, NAS326 firmware 5.21\(aazf.14\)c0.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Scores
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
41%
Higher than 98.6% of all scored CVEs
Exploit maturity
None known
ATLAS score
41/100
Publication score, see How it works
Exploitation Verdict
KEV listed
Apr 28, 2024
Federal due date
None
No federal due date
Ransomware use
Not reported
Attributed actors
None named
Exploit & Defence Guidance
Exploit maturity
None known
Public exploit code
0
Proof-of-concept links
In-the-wild evidence
5
Reports of active use
Advisories And Exploit References
- advisoryhttps://www.bleepingcomputer.com/news/security/zyxel-warns-of-multiple-critical-vulnerabilities-in-nas-devices/
- advisoryUSOM advisory
- advisoryhttps://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-authentication-bypass-and-command-injection-vulnerabilities-in-nas-products
Description
A command injection vulnerability in the web server of the Zyxel NAS326 firmware version V5.21(AAZF.14)C0 and NAS542 firmware version V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands by sending a crafted URL to a vulnerable device.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CIRCL KEV | Apr 28, 2024 | n/a | Not reported |
| Industry KEV feed | Apr 28, 2024 | n/a | Not reported |
Affected Products
4 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| NAS326 firmwareZyxel | >= V5.21(AAZF.14)C0 | 5.21\(aazf.14\)c0 |
| NAS542 firmwareZyxel | >= V5.21(ABAG.11)C0 | 5.21\(abag.11\)c0 |
Patched Releases
NAS326 firmware
<=5.21\(aazf.14\)c0
NAS542 firmware
<=5.21\(abag.11\)c0
Timeline
Publicly disclosed
Dec 1, 2023
Added to CIRCL KEV
Apr 28, 2024
Added to Industry KEV feed
Apr 28, 2024
Last updated
Dec 16, 2025
Weakness Type
- CWE-78 Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
References
- advisorybleepingcomputer.com · zyxel-warns-of-multiple-critical-vulnerabilitie…
- advisoryUSOM advisory
- advisoryzyxel.com · zyxel-security-advisory-for-authentication-bypa…
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
FAQ
Common Questions.
A command injection vulnerability in the web server of the Zyxel NAS326 firmware version V5.21(AAZF.14)C0 and NAS542 firmware version V5.21(ABAG.11)C0 could allow an unauthenticated attacker to execute some operating system (OS) commands by sending a crafted URL to a vulnerable device.
Affected: NAS326 firmware (Zyxel) versions >= V5.21(AAZF.14)C0; NAS542 firmware (Zyxel) versions >= V5.21(ABAG.11)C0. The full list is in the CVE brief.
It is exploited in the wild, listed in CIRCL KEV, Industry KEV feed since Apr 28, 2024.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
A public exploit is reported by tracking sources, but no code link is listed yet.
Fixed versions are available, including NAS326 firmware <=5.21\(aazf.14\)c0, NAS542 firmware <=5.21\(abag.11\)c0, NAS326 firmware 5.21\(aazf.14\)c0.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Is CVE-2023-4473 On Your Attack Surface?
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