# CVE-2026-1773: Denial of service in RTU500 series CMU firmware

> Attackers can cause denial of service in Hitachi RTU500 devices by sending invalid IEC 60870-5-104 frames when bi-directional functionality is enabled.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Feb 2026
- **Updated:** 27 May 2026
- **Also known as:** GHSA-q2vg-xgjr-32v3

## What is CVE-2026-1773?

CVE-2026-1773 is a high-severity denial of service vulnerability in Hitachi Energy RTU500 series CMU firmware, published on 24 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

IEC 60870-5-104 used in RTU500: Potential Denial of Service impact on reception of invalid U-format frame. Product is only affected if IEC 60870-5-104 bi-directional functionality is configured. Enabling secure communication following IEC 62351-3 does not remediate the vulnerability but mitigates the risk of exploitation.

Weakness: CWE-184 (Incomplete List of Disallowed Inputs)

## Which versions are affected by CVE-2026-1773?

It affects 4 products.


Products: Hitachienergy Rtu520 Firmware, Hitachienergy Rtu530 Firmware, Hitachienergy Rtu540 Firmware, Hitachienergy Rtu560 Firmware.

## How do I fix CVE-2026-1773?

No fix has been published for CVE-2026-1773 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-1773 being exploited?

There is no known exploitation of CVE-2026-1773 in the wild and no public exploit code.

## Other vulnerabilities in Hitachi Energy RTU500 series CMU firmware

- [CVE-2022-2081](https://insights.sbomify.com/CVE-2022-2081/): Denial of service in RTU500 series CMU firmware (high 7.5)
- [CVE-2023-5767](https://insights.sbomify.com/CVE-2023-5767/): Cross-site scripting in RTU500 (medium 6.0)
- [CVE-2023-5768](https://insights.sbomify.com/CVE-2023-5768/): Denial of service in RTU500 series (medium 5.9)
- [CVE-2023-5769](https://insights.sbomify.com/CVE-2023-5769/): Cross-site scripting in RTU500 (medium 5.4)
- [CVE-2026-1772](https://insights.sbomify.com/CVE-2026-1772/): Information disclosure in RTU500 series CMU firmware (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-1773 and fix it if it is affected.

What it is: CVE-2026-1773 is a high-severity denial of service vulnerability in Hitachi Energy RTU500 series CMU firmware, published on 24 Feb 2026. 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-2026-1773 in the wild and no public exploit code.

Affected product: Hitachi Energy RTU500 series CMU 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-2026-1773/ (Markdown: https://insights.sbomify.com/CVE-2026-1773/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-1773
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-1773
- OSV: https://osv.dev/vulnerability/CVE-2026-1773

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-1773/
Summaries are generated and may contain mistakes; the official description above is the record.