# CVE-2026-11826: OpenPLC_v3 Heap-Based Buffer Overflow in Modbus Master getData()

> An authenticated attacker can cause a heap buffer overflow in OpenPLC_v3 via the web interface, leading to denial of service and configuration corruption.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 18 Jul 2026
- **Updated:** 28 Jul 2026
- **Also known as:** GHSA-3x22-r5w3-j249

## What is CVE-2026-11826?

CVE-2026-11826 is a high-severity memory corruption vulnerability in openplcproject OpenPLC_v3, published on 18 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

OpenPLC_v3 contains a heap-based buffer overflow in the getData() function in webserver/core/modbus_master.cpp. getData() reads characters between two delimiters into a caller-supplied buffer with no size parameter and no bounds check. In parseConfig() the function is invoked with the 100-byte heap-allocated MB_device.dev_name field. An authenticated attacker with access to the OpenPLC web interface can send a crafted HTTP POST to the /modbus endpoint with an oversized device_name value; the value is persisted to mbconfig.cfg and parsed on load, overflowing dev_name and overwriting adjacent struct fields (protocol at offset 108, dev_address at offset 109, ip_port at offset 210). A 200-byte payload writes 100 bytes past the allocation. The result is heap corruption leading to runtime crash and denial of service of the PLC process control loop, with attacker-controlled overwrite of adjacent configuration fields. The upstream repository was archived on 2026-04-04 and no fix is expected; the vendor has confirmed the issue does not affect OpenPLC Runtime v4.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-11826?


## How do I fix CVE-2026-11826?

No fix has been published for CVE-2026-11826 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-11826 being exploited?

There is no known exploitation of CVE-2026-11826 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-11826 and fix it if it is affected.

What it is: CVE-2026-11826 is a high-severity memory corruption vulnerability in openplcproject OpenPLC_v3, published on 18 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-11826 in the wild and no public exploit code.

Affected product: openplcproject OpenPLC_v3. 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-2026-11826/ (Markdown: https://insights.sbomify.com/CVE-2026-11826/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-11826
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-11826
- OSV: https://osv.dev/vulnerability/CVE-2026-11826

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-11826/
Summaries are generated and may contain mistakes; the official description above is the record.