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

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

Which versions are affected by CVE-2026-27703?

It affects 1 product.

Products include 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.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

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 Buffer overflows in RIOT Critical 9.8
• CVE-2023-33975 RIOT-OS vulnerable to Out of Bounds Write in _rbuf_add Critical 9.8
• CVE-2023-24819 RIOT-OS vulnerable to Buffer Overflow during IPHC receive Critical 9.8
• CVE-2023-24823 RIOT-OS vulnerable to Packet Type Confusion during IPHC send Critical 9.8
• CVE-2021-27357 Memory corruption in n/a Critical 9.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-qgj4-9jff-93cj.