# CVE-2023-4397: Memory corruption in USG FLEX 50(W) series firmware

> An authenticated administrator can cause a denial-of-service condition on Zyxel firewalls by executing CLI commands with crafted strings.

- **Severity:** Medium 4.4 (`CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 28 Nov 2023
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-rx6q-hj2g-x8wp

## What is CVE-2023-4397?

CVE-2023-4397 is a medium-severity memory corruption vulnerability in Zyxel  USG FLEX 50(W) series firmware, published on 28 Nov 2023. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A buffer overflow vulnerability in the Zyxel ATP series firmware version 5.37, USG FLEX series firmware version 5.37, USG FLEX 50(W) series firmware version 5.37, and USG20(W)-VPN series firmware version 5.37, could allow an authenticated local attacker with administrator privileges to cause denial-of-service (DoS) conditions by executing the CLI command with crafted strings on an affected device.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2023-4397?

It affects 1 product.


Products: Zyxel Zld.

## How do I fix CVE-2023-4397?

No fix has been published for CVE-2023-4397 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-4397 being exploited?

There is no known exploitation of CVE-2023-4397 in the wild and no public exploit code.

## Other vulnerabilities in Zyxel  USG FLEX 50(W) series firmware

- [CVE-2024-11667](https://insights.sbomify.com/CVE-2024-11667/): Zyxel Multiple Firewalls Path Traversal (high 7.5, exploited in the wild)
- [CVE-2025-9133](https://insights.sbomify.com/CVE-2025-9133/): Missing authorization in ATP series firmware (high 8.1)
- [CVE-2024-42057](https://insights.sbomify.com/CVE-2024-42057/): Command injection in ATP series firmware (high 8.1)
- [CVE-2024-42058](https://insights.sbomify.com/CVE-2024-42058/): Null dereference in ATP series firmware (high 7.5)
- [CVE-2023-4398](https://insights.sbomify.com/CVE-2023-4398/): Integer overflow in ATP series firmware (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-4397 and fix it if it is affected.

What it is: CVE-2023-4397 is a medium-severity memory corruption vulnerability in Zyxel  USG FLEX 50(W) series firmware, published on 28 Nov 2023. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-4397 in the wild and no public exploit code.

Affected product: Zyxel  USG FLEX 50(W) series firmware. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2023-4397/ (Markdown: https://insights.sbomify.com/CVE-2023-4397/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-4397
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-4397
- OSV: https://osv.dev/vulnerability/CVE-2023-4397

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From sbomify Insights: https://insights.sbomify.com/CVE-2023-4397/
Summaries are generated and may contain mistakes; the official description above is the record.