# CVE-2019-18261: Auth bypass in Omron PLC CJ, CS and NJ Series

> Attackers can bypass authentication via brute force attacks on Omron PLCs due to missing rate limiting, potentially gaining unauthorized access.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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:** 16 Dec 2019
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-pgg2-jx97-c5m4

## What is CVE-2019-18261?

CVE-2019-18261 is a critical authentication bypass vulnerability in Omron PLC CJ, CS and NJ Series, published on 16 Dec 2019. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In Omron PLC CS series, all versions, Omron PLC CJ series, all versions, and Omron PLC NJ series, all versions, the software does not implement sufficient measures to prevent multiple failed authentication attempts within in a short time frame, making it more susceptible to brute force attacks.

Weakness: CWE-307 (Improper Restriction of Excessive Authentication Attempts)

## Which versions are affected by CVE-2019-18261?

It affects 3 products.


Products: Omron Plc Cj Firmware, Omron Plc Cs Firmware, Omron Plc Nj Firmware.

## How do I fix CVE-2019-18261?

No fix has been published for CVE-2019-18261 yet. Limit exposure of the affected software until one is available.

## Is CVE-2019-18261 being exploited?

There is no known exploitation of CVE-2019-18261 in the wild and no public exploit code.

## Other vulnerabilities in Omron PLC CJ, CS and NJ Series

- [CVE-2019-18259](https://insights.sbomify.com/CVE-2019-18259/): Other in Omron PLC CJ and CS Series (critical 9.8)
- [CVE-2019-18269](https://insights.sbomify.com/CVE-2019-18269/): Missing authorization in Omron PLC CJ Series (high 8.6)
- [CVE-2019-13533](https://insights.sbomify.com/CVE-2019-13533/): Other in Omron PLC CJ and CS Series (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2019-18261 and fix it if it is affected.

What it is: CVE-2019-18261 is a critical authentication bypass vulnerability in Omron PLC CJ, CS and NJ Series, published on 16 Dec 2019. 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-2019-18261 in the wild and no public exploit code.

Affected product: Omron PLC CJ, CS and NJ Series. 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-2019-18261/ (Markdown: https://insights.sbomify.com/CVE-2019-18261/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2019-18261
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2019-18261
- OSV: https://osv.dev/vulnerability/CVE-2019-18261

---
From sbomify Insights: https://insights.sbomify.com/CVE-2019-18261/
Summaries are generated and may contain mistakes; the official description above is the record.