Vulnerability · Published Oct 9, 2026 · Assigned by GitHub_M

CVE-2026-107838RIOT: nanocoap_fileserver ignores response initialization failure, leading to reachable assertion

High 7.5

In plain English

A high-severity security flaw in RIOT from RIOT-OS. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities).

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.3%top 72.5% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

RIOT is an open-source microcontroller operating system designed for Internet of Things devices and other embedded systems. From version 2023.07 through version 2026.07, nanocoap_fileserver callers in sys/net/application_layer/nanocoap/fileserver.c ignore a failure returned by _resp_init() when coap_build_reply() cannot fit a response header into the response buffer. A remote client can send a CoAP request with a sufficiently large extended token when nanocoap_token_ext is enabled, causing response initialization to fail while _get_file() or _get_directory() continues with stale response state. The path then reaches _calc_szx2() and its pdu->payload_len > reserve assertion, terminating the affected service or device task. No fixed release is available as of this review.

Affected products (as reported)

Vendor	Product	Versions
RIOT-OS	RIOT	>= 2023.07, <= 2026.07

Weakness: CWE-252, CWE-617 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2 x_refsource_CONFIRM
https://github.com/RIOT-OS/RIOT/pull/22745 x_refsource_MISC
https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743 x_refsource_MISC