{"id":"CVE-2026-107836","state":"PUBLISHED","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.","publishedAt":"2026-10-09T17:49:41.120Z","updatedAt":"2026-10-09T18:00:37.637Z","severity":{"score":7.1,"label":"High","version":"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","source":"GitHub_M"},"assigner":"GitHub_M","products":["RIOT-OS RIOT"],"affected":[{"vendor":"RIOT-OS","product":"RIOT","versions":[{"version":"<= 2026.07","status":"affected"}]}],"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"],"weaknesses":["CWE-125","CWE-191"],"ingestedAt":"2026-10-29T20:10:23.711Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/107xxx/CVE-2026-107836.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-107836","state":"PUBLISHED","datePublished":"2026-10-09T17:49:41.120Z","dateUpdated":"2026-10-09T18:00:37.637Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-10-08T22:34:49.289Z"},"containers":{"cna":{"title":"RIOT: nanoCoAP Block2 client slice handling underflows on inconsistent server-controlled block size","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"RIOT-OS","product":"RIOT","versions":[{"version":"<= 2026.07","status":"affected"}]}],"references":[{"url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","name":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/RIOT-OS/RIOT/pull/22518","name":"https://github.com/RIOT-OS/RIOT/pull/22518","tags":["x_refsource_MISC"]},{"url":"https://github.com/RIOT-OS/RIOT/commit/49b894cbe091510093273b98d92c4a17167d6839","name":"https://github.com/RIOT-OS/RIOT/commit/49b894cbe091510093273b98d92c4a17167d6839","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"PASSIVE","vulnConfidentialityImpact":"LOW","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":7.1,"baseSeverity":"HIGH","vectorString":"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","version":"4.0"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-125","lang":"en","description":"CWE-125: Out-of-bounds Read","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-191","lang":"en","description":"CWE-191: Integer Underflow (Wrap or Wraparound)","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-10-09T17:49:41.120Z"},"source":{"advisory":"GHSA-x924-p5fq-26pc","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-09T17:59:40.461358Z","id":"CVE-2026-107836","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-09T18:00:37.637Z"}}]}}}