RIOT-OS RIOT up to 2026.07 Fileserver fileserver.c _resp_init payload_len initialization

Summaryinfo

A vulnerability categorized as critical has been discovered in RIOT-OS RIOT up to 2026.07. This vulnerability affects the function _resp_init of the file sys/net/application_layer/nanocoap/fileserver.c of the component Fileserver. Executing a manipulation of the argument payload_len can lead to initialization. This vulnerability is registered as CVE-2026-107838. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability classified as critical was found in RIOT-OS RIOT up to 2026.07. This vulnerability affects the function _resp_init of the file sys/net/application_layer/nanocoap/fileserver.c of the component Fileserver. The manipulation of the argument payload_len with an unknown input leads to a initialization vulnerability. The CWE definition for the vulnerability is CWE-665. The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used. As an impact it is known to affect availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability was named CVE-2026-107838 since 10/09/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Vendor

• RIOT-OS

Name

• RIOT

Version

• 2026.07

Website

• Product: https://github.com/RIOT-OS/RIOT/

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