# CVE-2023-39240: ASUS RT-AX55、RT-AX56U_V2 - Format String - 3

> A format string vulnerability in the iperf client API allows remote administrators to execute arbitrary code or disrupt service on ASUS routers.

- **Severity:** High 7.2 (`CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 7 Sep 2023
- **Updated:** 26 Sep 2024
- **Also known as:** GHSA-pjc4-2x49-3j92

## What is CVE-2023-39240?

CVE-2023-39240 is a high-severity vulnerability in ASUS RT-AX55, published on 7 Sep 2023. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

It is identified a format string vulnerability in ASUS RT-AX56U V2’s iperf client function API. This vulnerability is caused by lacking validation for a specific value within its set_iperf3_cli.cgi module. A remote attacker with administrator privilege can exploit this vulnerability to perform remote arbitrary code execution, arbitrary system operation or disrupt service.

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

## Which versions are affected by CVE-2023-39240?

It affects 3 products.


Products: Asus Rt-Ac86u Firmware, Asus Rt-Ax55 Firmware, Asus Rt-Ax56u V2 Firmware.

## How do I fix CVE-2023-39240?

No fix has been published for CVE-2023-39240 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-39240 being exploited?

There is no known exploitation of CVE-2023-39240 in the wild and no public exploit code.

## Other vulnerabilities in ASUS RT-AX55

- [CVE-2023-35087](https://insights.sbomify.com/CVE-2023-35087/): ASUS RT-AX56U V2 & RT-AC86U - Format String - 2 (critical 9.8)
- [CVE-2023-38031](https://insights.sbomify.com/CVE-2023-38031/): ASUS RT-AC86U - Command injection vulnerability - 1 (high 8.8)
- [CVE-2023-38032](https://insights.sbomify.com/CVE-2023-38032/): ASUS RT-AC86U - Command injection vulnerability - 2 (high 8.8)
- [CVE-2023-38033](https://insights.sbomify.com/CVE-2023-38033/): ASUS RT-AC86U - Command injection vulnerability - 3 (high 8.8)
- [CVE-2023-39236](https://insights.sbomify.com/CVE-2023-39236/): ASUS RT-AC86U - Command injection vulnerability - 4 (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-39240 and fix it if it is affected.

What it is: CVE-2023-39240 is a high-severity vulnerability in ASUS RT-AX55, published on 7 Sep 2023. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2023-39240 in the wild and no public exploit code.

Affected product: ASUS RT-AX55. 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-2023-39240/ (Markdown: https://insights.sbomify.com/CVE-2023-39240/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-39240
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-39240
- OSV: https://osv.dev/vulnerability/CVE-2023-39240

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-39240/
Summaries are generated and may contain mistakes; the official description above is the record.