# CVE-2026-27703: RIOT has an Out-of-Bounds Write in nanoCoAP Handler

> An out-of-bounds write in RIOT OS nanoCoAP handler allows attackers to corrupt memory, potentially leading to arbitrary code execution or denial of service.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 11 Mar 2026
- **Updated:** 12 Mar 2026
- **Also known as:** GHSA-qgj4-9jff-93cj

## What is CVE-2026-27703?

CVE-2026-27703 is a high-severity memory corruption vulnerability in RIOT-OS RIOT, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

RIOT is an open-source microcontroller operating system, designed to match the requirements of Internet of Things (IoT) devices and other embedded devices. In 2026.01 and earlier, the default handler for the well_known_core resource coap_well_known_core_default_handler writes user-provided option data and other data into a fixed size buffer without validating the buffer is large enough to contain the response. This vulnerability allows an attacker to corrupt neighboring stack location, including security-sensitive addresses like the return address, leading to denial of service or arbitrary code execution.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-27703?

It affects 1 product.


Products: Riot-Os Riot.

## How do I fix CVE-2026-27703?

No fix has been published for CVE-2026-27703 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-27703 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27703 exists.

## Other vulnerabilities in RIOT-OS RIOT

- [CVE-2024-32017](https://insights.sbomify.com/CVE-2024-32017/): Buffer overflows in RIOT (critical 9.8)
- [CVE-2023-33975](https://insights.sbomify.com/CVE-2023-33975/): RIOT-OS vulnerable to Out of Bounds Write in _rbuf_add (critical 9.8)
- [CVE-2023-24819](https://insights.sbomify.com/CVE-2023-24819/): RIOT-OS vulnerable to Buffer Overflow during IPHC receive (critical 9.8)
- [CVE-2023-24823](https://insights.sbomify.com/CVE-2023-24823/): RIOT-OS vulnerable to Packet Type Confusion during IPHC send (critical 9.8)
- [CVE-2021-27357](https://insights.sbomify.com/CVE-2021-27357/): Memory corruption in n/a (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27703 and fix it if it is affected.

What it is: CVE-2026-27703 is a high-severity memory corruption vulnerability in RIOT-OS RIOT, published on 11 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27703 exists.

Affected product: RIOT-OS RIOT. 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-2026-27703/ (Markdown: https://insights.sbomify.com/CVE-2026-27703/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27703
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27703
- OSV: https://osv.dev/vulnerability/CVE-2026-27703

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27703/
Summaries are generated and may contain mistakes; the official description above is the record.