# CVE-2021-20598: Denial of service in MELSEC iQ-R series CPU modules R08/16/32/120SFCPU; R08/16/32/120PSFCPU

> Remote attackers can lock out legitimate users by repeatedly attempting incorrect logins, causing denial of service on Mitsubishi MELSEC iQ-R CPU modules.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Aug 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-f5j9-pg8j-928p

## What is CVE-2021-20598?

CVE-2021-20598 is a medium-severity denial of service vulnerability in MELSEC iQ-R series CPU modules R08/16/32/120SFCPU; R08/16/32/120PSFCPU, published on 6 Aug 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Overly Restrictive Account Lockout Mechanism vulnerability in Mitsubishi Electric MELSEC iQ-R series CPU modules (R08/16/32/120SFCPU all versions, R08/16/32/120PSFCPU all versions) allows a remote unauthenticated attacker to lockout a legitimate user by continuously trying login with incorrect password.

Weakness: CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2021-20598?

It affects 8 products.


Products: Mitsubishielectric R08psfcpu Firmware, Mitsubishielectric R08sfcpu Firmware, Mitsubishielectric R120psfcpu Firmware, Mitsubishielectric R120sfcpu Firmware, Mitsubishielectric R16psfcpu Firmware, Mitsubishielectric R16sfcpu Firmware, Mitsubishielectric R32psfcpu Firmware, Mitsubishielectric R32sfcpu Firmware.

## How do I fix CVE-2021-20598?

No fix has been published for CVE-2021-20598 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-20598 being exploited?

There is no known exploitation of CVE-2021-20598 in the wild and no public exploit code.

## Other vulnerabilities in MELSEC iQ-R series CPU modules R08/16/32/120SFCPU; R08/16/32/120PSFCPU

- [CVE-2021-20599](https://insights.sbomify.com/CVE-2021-20599/): Information disclosure in MELSEC iQ-R Series SIL2 Process CPU R08PSFCPU (critical 9.1)
- [CVE-2021-20597](https://insights.sbomify.com/CVE-2021-20597/): Information disclosure in Mitsubishi Electric MELSEC iQ-R series Safety CPU modules R08/16/32/120SFCPU; Mitsubishi Electric MELSEC iQ-R series SIL2 Process CPU modules R08/16/32/120PSFCPU (critical 9.1)
- [CVE-2021-20594](https://insights.sbomify.com/CVE-2021-20594/): Information disclosure in Mitsubishi Electric MELSEC iQ-R series Safety CPU modules R08/16/32/120SFCPU; Mitsubishi Electric MELSEC iQ-R series SIL2 Process CPU modules R08/16/32/120PSFCPU (high 7.5)
- [CVE-2023-6815](https://insights.sbomify.com/CVE-2023-6815/): Information disclosure in MELSEC iQ-R Series SIL2 Process CPU R08PSFCPU (medium 6.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20598 and fix it if it is affected.

What it is: CVE-2021-20598 is a medium-severity denial of service vulnerability in MELSEC iQ-R series CPU modules R08/16/32/120SFCPU; R08/16/32/120PSFCPU, published on 6 Aug 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-2021-20598 in the wild and no public exploit code.

Affected product: MELSEC iQ-R series CPU modules R08/16/32/120SFCPU; R08/16/32/120PSFCPU. 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-2021-20598/ (Markdown: https://insights.sbomify.com/CVE-2021-20598/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20598
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20598
- OSV: https://osv.dev/vulnerability/CVE-2021-20598

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-20598/
Summaries are generated and may contain mistakes; the official description above is the record.