# CVE-2023-6399: Denial of service in USG FLEX 50(W) series firmware

> An authenticated IPSec VPN user can cause a denial of service against the deviceid daemon by sending a crafted hostname if Device Insight is enabled.

- **Severity:** Medium 5.7 (`CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 20 Feb 2024
- **Updated:** 2 Aug 2024
- **Also known as:** GHSA-6mfv-h538-gwvr

## What is CVE-2023-6399?

CVE-2023-6399 is a medium-severity denial of service vulnerability in Zyxel  USG FLEX 50(W) series firmware, published on 20 Feb 2024. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A format string vulnerability in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4.50 through 5.37 Patch 1, USG FLEX 50(W) series firmware versions from 4.16 through 5.37 Patch 1, USG20(W)-VPN series firmware versions from 4.16 through 5.37 Patch 1, and USG FLEX H series firmware versions from 1.10 through 1.10 Patch 1 could allow an authenticated IPSec VPN user to cause DoS conditions against the “deviceid” daemon by sending a crafted hostname to an affected device if it has the “Device Insight” feature enabled.

Weakness: CWE-134 (Use of Externally-Controlled Format String)

## Which versions are affected by CVE-2023-6399?

It affects 22 products.


Products: Zyxel Atp100 Firmware, Zyxel Atp100w Firmware, Zyxel Atp200 Firmware, Zyxel Atp500 Firmware, Zyxel Atp700 Firmware, Zyxel Atp800 Firmware, Zyxel Uos, Zyxel Usg20-Vpn Firmware, Zyxel Usg20w-Vpn Firmware, Zyxel Usg Flex 100 Firmware, Zyxel Usg Flex 100ax Firmware, Zyxel Usg Flex 100h Firmware, Zyxel Usg Flex 100w Firmware, Zyxel Usg Flex 200 Firmware, Zyxel Usg Flex 200h Firmware, Zyxel Usg Flex 200hp Firmware, Zyxel Usg Flex 500 Firmware, Zyxel Usg Flex 500h Firmware, Zyxel Usg Flex 50 Firmware, Zyxel Usg Flex 50w Firmware and 2 more.

## How do I fix CVE-2023-6399?

No fix has been published for CVE-2023-6399 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-6399 being exploited?

There is no known exploitation of CVE-2023-6399 in the wild and no public exploit code.

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

- [CVE-2023-33009](https://insights.sbomify.com/CVE-2023-33009/): Zyxel Multiple Firewalls Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2023-33010](https://insights.sbomify.com/CVE-2023-33010/): Zyxel Multiple Firewalls Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2023-28771](https://insights.sbomify.com/CVE-2023-28771/): Zyxel Multiple Firewalls OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2022-30525](https://insights.sbomify.com/CVE-2022-30525/): Zyxel Multiple Firewalls OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2020-29583](https://insights.sbomify.com/CVE-2020-29583/): Zyxel Multiple Products Use of Hard-Coded Credentials (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-6399 and fix it if it is affected.

What it is: CVE-2023-6399 is a medium-severity denial of service vulnerability in Zyxel  USG FLEX 50(W) series firmware, published on 20 Feb 2024. 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-2023-6399 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-2023-6399/ (Markdown: https://insights.sbomify.com/CVE-2023-6399/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-6399
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-6399
- OSV: https://osv.dev/vulnerability/CVE-2023-6399

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From sbomify Insights: https://insights.sbomify.com/CVE-2023-6399/
Summaries are generated and may contain mistakes; the official description above is the record.