Contiki-NG DNS/mDNS Resolver Out-of-Bounds Read via Unchecked skip_name Traversal Before Transaction-ID Validation
Summary
| CVE | CVE-2026-5856 |
|---|---|
| State | PUBLISHED |
| Assigner | VulnCheck |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-08-06 22:18:10 UTC |
| Updated | 2026-08-07 18:17:19 UTC |
| Description | 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. |
Risk And Classification
Primary CVSS: v4.0 7.1 HIGH from [email protected]
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS: 0.002530000 probability, percentile 0.167400000 (date 2026-08-07)
Problem Types: CWE-125 | CWE-125 CWE-125 Out-of-bounds read
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | [email protected] | Secondary | 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/E:X/C... |
| 4.0 | CNA | CVSS | 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 |
| 3.1 | [email protected] | Secondary | 7.1 | HIGH | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L |
| 3.1 | CNA | CVSS | 7.1 | HIGH | CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L |
CVSS v4.0 Breakdown
Attack Vector
AdjacentAttack Complexity
LowAttack Requirements
NonePrivileges Required
NoneUser Interaction
NoneConfidentiality
HighIntegrity
NoneAvailability
LowSub Conf.
NoneSub Integrity
NoneSub Availability
NoneCVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:L/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/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CVSS v3.1 Breakdown
Attack Vector
AdjacentAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
HighIntegrity
NoneAvailability
LowCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Contiki-NG | Contiki-NG | affected 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe custom | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/contiki-ng/contiki-ng | [email protected] | github.com | |
| github.com/contiki-ng/contiki-ng/pull/3169 | [email protected] | github.com | |
| github.com/contiki-ng/contiki-ng/commit/04a3f0a0067d2ee87d1f297b6d0f4392... | [email protected] | github.com | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Kazuma Matsumoto, a security researcher at GMO Cybersecurity by IERAE, Inc. (en)
There are currently no legacy QID mappings associated with this CVE.