{"id":"CVE-2026-107836","revision":"a4099cdff1c2442b91505521179e295c","records":[{"revision":"a4099cdff1c2442b91505521179e295c","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-107836","aliases":[],"title":"RIOT: nanoCoAP Block2 client slice handling underflows on inconsistent server-controlled block size","description":"RIOT is an open-source microcontroller operating system designed for Internet of Things devices and other embedded systems. In 2026.07 and earlier, the nanoCoAP client function nanocoap_sock_get_slice() in sys/net/application_layer/nanocoap/sock.c accepts a Block2 response when _block_cb() sees the expected block number without also verifying that the server-controlled szx and derived offset match the requested block geometry. A malicious CoAP server can return the expected block number with a larger block size, causing the derived offset to exceed the client slice offset and making ctx->offset - offset underflow in _2buf_slice(). The resulting buffer-relative calculation can read before the payload buffer and crash the client, causing denial of service and potentially exposing adjacent memory. No fixed release is available as of this review.","state":0,"publishedAt":"2026-10-09T17:49:41.12+00:00","modifiedAt":"2026-10-09T18:00:37.637+00:00","affected":[{"ecosystem":"Vendor product","name":"RIOT","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"RIOT-OS\",\n                    \"product\": \"RIOT\",\n                    \"versions\": [\n                        {\n                            \"version\": \"<= 2026.07\",\n                            \"status\": \"affected\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:N/VA:H/SC:N/SI:N/SA:N","score":7.1,"severity":"HIGH"}],"references":["https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","https://github.com/RIOT-OS/RIOT/pull/22518","https://github.com/RIOT-OS/RIOT/commit/49b894cbe091510093273b98d92c4a17167d6839"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-107836","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-107836","identifiers":["CVE-2026-107836"]},"retained":false,"historicalAffected":[]}],"coverage":[]}