# CVE-2021-20591: Denial of service in MELSEC iQ-R series CPU modules

> Remote unauthenticated attackers can cause denial of service on Mitsubishi MELSEC iQ-R CPU modules by exhausting connection resources.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-mhpv-hfp2-2648

## What is CVE-2021-20591?

CVE-2021-20591 is a high-severity denial of service vulnerability in MELSEC iQ-R series CPU modules, published on 11 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Uncontrolled Resource Consumption vulnerability in Mitsubishi Electric MELSEC iQ-R series CPU modules (R00/01/02CPU all versions, R04/08/16/32/120(EN)CPU all versions, R08/16/32/120SFCPU all versions, R08/16/32/120PCPU all versions, R08/16/32/120PSFCPU all versions) allows a remote unauthenticated attacker to prevent legitimate clients from connecting to the MELSOFT transmission port (TCP/IP) by not closing a connection properly, which may lead to a denial of service (DoS) condition.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-20591?

It affects 20 products.


Products: Mitsubishielectric R00cpu Firmware, Mitsubishielectric R01cpu Firmware, Mitsubishielectric R02cpu Firmware, Mitsubishielectric R04cpu Firmware, Mitsubishielectric R08cpu Firmware, Mitsubishielectric R08pcpu Firmware, Mitsubishielectric R08psfcpu Firmware, Mitsubishielectric R08sfcpu Firmware, Mitsubishielectric R120cpu Firmware, Mitsubishielectric R120pcpu Firmware, Mitsubishielectric R120psfcpu Firmware, Mitsubishielectric R120sfcpu Firmware, Mitsubishielectric R16cpu Firmware, Mitsubishielectric R16pcpu Firmware, Mitsubishielectric R16psfcpu Firmware, Mitsubishielectric R16sfcpu Firmware, Mitsubishielectric R32cpu Firmware, Mitsubishielectric R32pcpu Firmware, Mitsubishielectric R32psfcpu Firmware, Mitsubishielectric R32sfcpu Firmware.

## How do I fix CVE-2021-20591?

No fix has been published for CVE-2021-20591 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20591 being exploited?

There is no known exploitation of CVE-2021-20591 in the wild and no public exploit code.

## Other vulnerabilities in MELSEC iQ-R series CPU modules

- [CVE-2020-16850](https://insights.sbomify.com/CVE-2020-16850/): Denial of service in n/a (high 7.5)
- [CVE-2020-5668](https://insights.sbomify.com/CVE-2020-5668/): Denial of service in MELSEC iQ-R (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20591 and fix it if it is affected.

What it is: CVE-2021-20591 is a high-severity denial of service vulnerability in MELSEC iQ-R series CPU modules, published on 11 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-20591 in the wild and no public exploit code.

Affected product: MELSEC iQ-R series CPU modules. 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-2021-20591/ (Markdown: https://insights.sbomify.com/CVE-2021-20591/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20591
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20591
- OSV: https://osv.dev/vulnerability/CVE-2021-20591

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-20591/
Summaries are generated and may contain mistakes; the official description above is the record.