# CVE-2026-17539: Null dereference in RTU500 series CMU firmware

> High-load IEC 104 requests trigger a NULL pointer dereference in Hitachi RTU500 firmware, causing connection restarts and denial of service.

- **Severity:** Medium 5.9 (`CVSS:3.1/AV:N/AC:H/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:** 3 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** GHSA-9w2f-4f52-qcj4

## What is CVE-2026-17539?

CVE-2026-17539 is a medium-severity vulnerability in Hitachi Energy RTU500 series CMU firmware, published on 3 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

RTU500 has a vulnerability, where high-load scenarios, such as sending GI requests at short intervals, may cause a NULL pointer dereference in the last entry of the enhanced message queue. This can cause a BCI_IEC104 fatal write error, resulting in connection interruption and restart, and ultimately a denial of service for bidirectional IEC 60870-5-104 communication.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-17539?


## How do I fix CVE-2026-17539?

No fix has been published for CVE-2026-17539 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-17539 being exploited?

There is no known exploitation of CVE-2026-17539 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-17539 and fix it if it is affected.

What it is: CVE-2026-17539 is a medium-severity vulnerability in Hitachi Energy RTU500 series CMU firmware, published on 3 Sep 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-2026-17539 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-2026-17539/ (Markdown: https://insights.sbomify.com/CVE-2026-17539/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-17539
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-17539
- OSV: https://osv.dev/vulnerability/CVE-2026-17539

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-17539/
Summaries are generated and may contain mistakes; the official description above is the record.