{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-5857","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","state":"PUBLISHED","assignerShortName":"VulnCheck","dateReserved":"2026-04-08T19:29:27.852Z","datePublished":"2026-08-06T18:52:40.005Z","dateUpdated":"2026-08-14T16:50:27.644Z"},"containers":{"cna":{"providerMetadata":{"orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","shortName":"VulnCheck","dateUpdated":"2026-08-14T16:50:27.644Z"},"title":"Contiki-NG MQTT Client Out-of-Bounds Write in PUBLISH Topic Parser via Persistent State Between TCP Segments","descriptions":[{"lang":"en","value":"Contiki-NG's MQTT client parse_publish_vhdr() in os/net/app-layer/mqtt/mqtt.c sets topic_len_received=1 before checking topic_len against the 64-byte limit, so an over-length topic returns early but leaves the flag set. On the next TCP segment, tcp_input() re-invokes the parser with topic_received==0, and the persisted topic_len_received==1 skips the length-reading block containing the guard, falling through directly to a memcpy() that uses the unvalidated 16-bit topic_len as the copy length. The 65-byte topic[] destination overruns into adjacent struct fields including the payload_chunk pointer, which subsequent MQTT code dereferences, giving a compromised or attacker-controlled broker an arbitrary-pointer-write primitive. Contiki-NG's MQTT implementation has no TLS support so the connection is plaintext. Impact ranges from information disclosure and denial of service to remote code execution on embedded targets without memory protection."}],"datePublic":"2026-08-06T00:00:00.000Z","problemTypes":[{"descriptions":[{"lang":"en","cweId":"CWE-787","description":"Out-of-bounds Write","type":"CWE"}]}],"affected":[{"vendor":"Contiki-NG","product":"Contiki-NG","versions":[{"status":"affected","version":"0","lessThan":"a34a2dbdc8bea784bd2ae5079aa4be520cd74f2d","versionType":"custom"}],"defaultStatus":"affected"}],"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:contiki-ng:contiki-ng:*:*:*:*:*:*:*:*"}]}]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV3_1":{"attackVector":"NETWORK","attackComplexity":"HIGH","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"HIGH","availabilityImpact":"HIGH","version":"3.1","baseSeverity":"HIGH","baseScore":8.1,"vectorString":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"}},{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"HIGH","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","subConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","subIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED","version":"4.0","baseSeverity":"CRITICAL","baseScore":9.2,"vectorString":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"}}],"references":[{"url":"https://github.com/contiki-ng/contiki-ng","tags":["product"]},{"url":"https://github.com/contiki-ng/contiki-ng/pull/3163","tags":["issue-tracking"]},{"url":"https://github.com/contiki-ng/contiki-ng/commit/a34a2dbdc8bea784bd2ae5079aa4be520cd74f2d","tags":["patch"]},{"url":"https://y637f9qq2x.com/posts/cve-2026-5857/","name":"Blog Post","tags":["technical-description"]}],"credits":[{"lang":"en","value":"Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc.","type":"reporter"}],"source":{"discovery":"UNKNOWN"},"x_generator":{"engine":"vulncheck"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-08T02:27:49.447800Z","id":"CVE-2026-5857","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-08-08T02:28:04.156Z"}}]}}