{"id":"CVE-2026-107838","state":"PUBLISHED","title":"RIOT: nanocoap_fileserver ignores response initialization failure, leading to reachable assertion","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.","publishedAt":"2026-10-09T17:55:34.670Z","updatedAt":"2026-10-13T17:07:38.700Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["RIOT-OS RIOT"],"affected":[{"vendor":"RIOT-OS","product":"RIOT","versions":[{"version":">= 2023.07, <= 2026.07","status":"affected"}]}],"references":["https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2","https://github.com/RIOT-OS/RIOT/pull/22745","https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743"],"weaknesses":["CWE-252","CWE-617"],"ingestedAt":"2026-10-29T20:10:23.711Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/107xxx/CVE-2026-107838.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-107838","state":"PUBLISHED","datePublished":"2026-10-09T17:55:34.670Z","dateUpdated":"2026-10-13T17:07:38.700Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-10-08T22:34:49.290Z"},"containers":{"cna":{"title":"RIOT: nanocoap_fileserver ignores response initialization failure, leading to reachable assertion","descriptions":[{"lang":"en","value":"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":[{"vendor":"RIOT-OS","product":"RIOT","versions":[{"version":">= 2023.07, <= 2026.07","status":"affected"}]}],"references":[{"url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2","name":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-39j3-3v73-5mj2","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/RIOT-OS/RIOT/pull/22745","name":"https://github.com/RIOT-OS/RIOT/pull/22745","tags":["x_refsource_MISC"]},{"url":"https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743","name":"https://github.com/RIOT-OS/RIOT/commit/d3a47289c58d108575a19e623e4d3f647659e743","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-252","lang":"en","description":"CWE-252: Unchecked Return Value","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-617","lang":"en","description":"CWE-617: Reachable Assertion","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-10-09T17:55:34.670Z"},"source":{"advisory":"GHSA-39j3-3v73-5mj2","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-13T17:07:15.908632Z","id":"CVE-2026-107838","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-13T17:07:38.700Z"}}]}}}