---
title: "CVE-2026-107838: RIOT - Denial of Service"
description: "RIOT 2023.07 through 2026.07 contains a denial of service caused by ignoring failure from _resp_init() when coap_build_reply() cannot fit a response header, letting remote clients with large extended tokens terminate service, exploit requires nanocoap_token_ext enabled."
url: https://panop.io/threat-heartbeat/CVE-2026-107838/
---

# CVE-2026-107838 RIOT - Denial of Service

RIOT 2023.07 through 2026.07 contains a denial of service caused by ignoring failure from \_resp\_init() when coap\_build\_reply() cannot fit a response header, letting remote clients with large extended tokens terminate service, exploit requires nanocoap\_token\_ext enabled.

CVSS base score 7.5 /10

High

CISA KEV

Not listed

Public exploit

None known

EPSS

0.34% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2026-107838)

## Details

Type

Denial of Service

Impact

Denial Of Service

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published

9 October 2026

Updated

15 October 2026

Weakness

[CWE-252](https://cwe.mitre.org/data/definitions/252.html)

## Vendor fix

Update to the latest version once a fix is released.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2026-107838](https://nvd.nist.gov/vuln/detail/CVE-2026-107838)
- [https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743](https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743)
- [https://github.com/RIOT-OS/RIOT/pull/22745](https://github.com/RIOT-OS/RIOT/pull/22745)
- [https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2](https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2)

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## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

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