{"id":"CVE-2026-107838","published":"2026-10-09T18:17:05.640","lastModified":"2026-10-13T18:17:15.987","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.","cvssScore":7.5,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","cwes":["CWE-252","CWE-617"],"vendors":[],"products":[],"references":[{"url":"https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743","tags":[]},{"url":"https://github.com/RIOT-OS/RIOT/pull/22745","tags":[]},{"url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2","tags":[]}],"exploitRefs":[{"url":"https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743","tags":[]},{"url":"https://github.com/RIOT-OS/RIOT/pull/22745","tags":[]},{"url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2","tags":[]}],"hasPoc":true,"ai":{"summary":"A flaw in RIOT OS's nanocoap_fileserver allows remote attackers to cause a service crash or device task termination by sending a specially crafted CoAP request with an extended token. This occurs when response initialization fails but the system continues processing with stale state, leading to assertion failures and system instability.","exploitability":"Exploitation is moderately difficult as it requires sending a specific CoAP request with a large extended token to a device running nanocoap_token_ext, but the attack can be automated and doesn't require special privileges.","blast_radius":"The impact could affect many IoT devices running RIOT OS versions 2023.07 through 2026.07, potentially causing widespread service disruption or device unavailability across connected systems.","remediation":"Disable nanocoap_token_ext functionality until a fixed version is available, as no specific release with a fix is mentioned in the description.","detection":"No reliable host or network indicator is derivable from the published description.","tags":["iot","coap","embedded","dos"],"model":"garnet-coder","analyzedAt":"2026-10-17T09:00:31.594Z"}}