CVE-2026-5856 (GCVE-0-2026-5856)

Vulnerability from cvelistv5 – Published: 2026-08-06 18:47 – Updated: 2026-08-14 16:50
VLAI
Title
Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation
Summary
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.
Severity
7.1 (High)
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L
7.1 (High)
CVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-08-07 17:40 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Contiki-NG Contiki-NG Affected: 0 , < 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe (custom)
    cpe:2.3:o:contiki-ng:contiki-ng:*:*:*:*:*:*:*:*
Create a notification for this product.
Date Public
2026-08-06 19:00
Credits
Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc.
Show details on NVD website
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