{"schema":"threatline.record/2","record":{"id":"CVE-2026-107836","aliases":["GHSA-x924-p5fq-26pc"],"summary":"RIOT: nanoCoAP Block2 client slice handling underflows on inconsistent server-controlled block size","details":"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.","categories":["Unclassified"],"product":"RIOT","vendor":"RIOT-OS","ecosystem":null,"affected_ranges":[{"source":"CVE List","source_url":"https://www.cve.org/CVERecord?id=CVE-2026-107836","source_modified_at":"2026-10-09T18:00:37.637Z","fetched_at":"2026-10-23T18:48:36.087640Z","product":"RIOT","vendor":"RIOT-OS","versions":[{"status":"affected","version":"<= 2026.07"}],"defaultStatus":null},{"source":"GitHub Advisory Database","source_url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","source_modified_at":"2026-10-09T17:47:50Z","fetched_at":"2026-10-23T18:52:38.922436Z","package":{"ecosystem":"riot","name":"RIOT"},"range":"<= master (verified on current master logic after PR #22498)"}],"fixed_versions":[],"cvss":7.1,"severity":"High","kev":{"listed":false},"epss":{"probability":0.00294,"percentile":0.20865,"score_date":"2026-10-23"},"published_at":"2026-10-09T17:49:41.120Z","modified_at":"2026-10-09T18:00:37.637Z","provenance":[{"source":"CVE List","url":"https://www.cve.org/CVERecord?id=CVE-2026-107836","fetched_at":"2026-10-23T18:48:36.087640Z","source_modified_at":"2026-10-09T18:00:37.637Z"},{"source":"GitHub Advisory Database","url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","fetched_at":"2026-10-23T18:52:38.922436Z","source_modified_at":"2026-10-09T17:47:50Z"},{"source":"EPSS","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-107836","fetched_at":"2026-10-23T18:42:43.628194Z","source_modified_at":"2026-10-23"}],"sources":["CVE List","GitHub Advisory Database","EPSS"],"references":[{"source":"CVE List","url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","tags":["x_refsource_CONFIRM"]},{"source":"CVE List","url":"https://github.com/RIOT-OS/RIOT/pull/22518","tags":["x_refsource_MISC"]},{"source":"CVE List","url":"https://github.com/RIOT-OS/RIOT/commit/49b894cbe091510093273b98d92c4a17167d6839","tags":["x_refsource_MISC"]}],"locations":[],"motoko_assessment":{"status":"requires_architecture_review","automatic_remediation":false},"cve_state":"PUBLISHED","cvss_source":"CVE List","ssvc":{"exploitation":"none","automatable":"no","technical_impact":"partial","assessed_at":"2026-10-09T17:59:40.461358Z"},"classification":{"method":"product-first software-layer rules","rules_version":"2.1","matched_on":null,"confidence":"unknown","reviewed":false},"change_timestamp":"2026-10-09T18:00:37.637Z","content_hash":"1b1670ff73703cc2c7509829dbb76345d0c37f481ae3c6900145350a4bd519c4"}}