{"id":"CVE-2026-107836","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-107836","generatedAt":"2026-10-28T02:14:24.307Z","title":"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().","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.","published":"2026-10-09T18:17:05.000Z","lastModified":"2026-10-16T17:17:04.000Z","status":"Deferred","sourceIdentifier":"security-advisories@github.com","cvss":{"version":"4.0","score":7.1,"severity":"HIGH","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-125","CWE-191"],"affected":[],"epss":{"score":0.00294,"percentile":0.21793,"date":"2026-10-26","history":[{"date":"2026-10-10","score":0.00294,"percentile":0.20207}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.29%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-10-09T18:17:05.000Z","detail":{"score":"7.1","severity":"HIGH","publishedAt":"2026-10-09T18:17:05.310Z"},"summary":"New CVE, high severity (CVSS 7.1)."}],"references":[{"url":"https://github.com/RIOT-OS/RIOT/commit/49b894cbe091510093273b98d92c4a17167d6839","source":"security-advisories@github.com"},{"url":"https://github.com/RIOT-OS/RIOT/pull/22518","source":"security-advisories@github.com"},{"url":"https://github.com/RIOT-OS/RIOT/security/advisories/GHSA-x924-p5fq-26pc","source":"security-advisories@github.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-107836","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}