# Zyxel Multiple Firewalls: OS Command Injection (CVE-2023-28771) · pwn.watch

> Zyxel ATP, USG FLEX, VPN, and ZyWALL/USG firewalls allow for improper error message handling which could allow an unauthenticated attacker to execute OS commands remotely by sending crafted packets to an affected device. Added to CISA KEV on 2023-05-31.

Page: https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771 · generated 2026-10-22T19:29:07.289Z

## Status
- Severity: critical · status: closed · patch: patched
- Product: Zyxel Multiple Firewalls
- Started: 2023-05-31 · closed: 2023-05-31
- CVEs: CVE-2023-28771
- Affected: See vendor advisory / CISA notes (versions not always listed in KEV feed)
- Fixed in: See vendor advisory linked in sources

## Follow this incident
- RSS (one item per update): https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771/feed.xml
- JSON Feed: https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771/feed.json
- Full data (timeline, sources, posts, agentBrief): https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771.json
- This file: https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771/llms.txt

## Updates (newest first)
- 2023-05-31: CISA added CVE-2023-28771 to the KEV catalog (due 2023-06-21).

## Fix brief
# Security brief: Zyxel Multiple Firewalls: OS Command Injection (CVE-2023-28771)

Source: https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771 · status: closed (closed May 31, 2023) · severity: critical · updated May 31, 2023

## Patch status
**PATCHED: fixed releases exist. Upgrade to a fixed version.**

## What it is
Zyxel ATP, USG FLEX, VPN, and ZyWALL/USG firewalls allow for improper error message handling which could allow an unauthenticated attacker to execute OS commands remotely by sending crafted packets to an affected device. Added to CISA KEV on 2023-05-31.

Severity detail: CVSS 9.8 (NVD), actively exploited (CISA KEV)

- Product: Zyxel Multiple Firewalls
- CVE / advisory ids: CVE-2023-28771

## Affected versions
- See vendor advisory / CISA notes (versions not always listed in KEV feed)

## Check whether you're affected
No generic command applies (the product is a hosted service, appliance or desktop app). Check the installed version in its admin UI / About screen and compare with the versions above.

## Fix
Upgrade to one of these fixed versions (or later on the same branch):
- See vendor advisory linked in sources

After upgrading, re-run the checks above and redeploy/restart the affected services.

## Latest updates
- May 31, 2023: CISA added CVE-2023-28771 to the KEV catalog (due 2023-06-21).

## Advisories
- [Vendor advisory: Zyxel Multiple Firewalls](https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-remote-command-injection-vulnerability-of-firewalls) (Zyxel)
- [NVD: CVE-2023-28771](https://nvd.nist.gov/vuln/detail/CVE-2023-28771) (NVD)
- [CISA Known Exploited Vulnerabilities Catalog](https://www.cisa.gov/known-exploited-vulnerabilities-catalog) (CISA)

## Caveats
Derived from CISA KEV JSON feed catalogVersion 2026.10.21. Exact affected/fixed version strings are not always in the KEV record — verify against the vendor advisory URL. startedAt uses dateAdded (exploitation may have begun earlier).

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Machine-readable: https://pwn.watch/i/zyxel-multiple-firewalls-cve-2023-28771.json · all incidents: https://pwn.watch/incidents.json. Verify against the vendor advisory before changing production systems.