Status: NEW | Advisory ID: CVE-2026-5856
| CVE | CVE-2026-5856 |
| CVSS Score / Version | 7.1 (High) / CVSS v3.1 |
| Updated | 2026-09-16 |
| CVSS Vector | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L |
| CVSS Prose | attack vector is adjacent; attack complexity is low; privileges required is none; user interaction is none; scope is unchanged; confidentiality impact is high; integrity impact is none; availability impact is low. |
| Classified as | CWE-125 (Out-of-bounds Read) |
Contiki-NG's DNS/mDNS resolver skip_name() in os/services/resolv/resolv.c walks DNS wire-format name labels with no packet-boundary check, and the caller in newdata() invokes it in a loop iterating nquestions times from the attacker-controlled DNS header before validating the transaction ID. An attacker who sets nquestions higher than the number of complete questions present causes skip_name() to walk past the UDP packet buffer, and the returned pointer is cast to struct dns_answer * for further memory reads. On builds with RESOLV_CONF_SUPPORTS_MDNS enabled, any peer on the local segment can trigger the read unauthenticated via a multicast UDP 5353 packet with no outstanding query required; on standard DNS builds an attacker who can inject a UDP response from port 53 during an outstanding query can trigger the same read. Impact is out-of-bounds read of uip_buf and adjacent memory, disclosing memory contents or crashing the resolver. (NVD)
| Source | Reference |
|---|---|
| NVD | https://nvd.nist.gov/vuln/detail/CVE-2026-5856 |
| CVE | https://www.cve.org/CVERecord?id=CVE-2026-5856 |