CVE-2026-5856

Disclosure or crash via unchecked DNS name traversal

Published Aug 6, 2026 · Updated Aug 6, 2026

Out-of-bounds read in the Contiki-NG DNS/mDNS resolver allows attackers to disclose memory or crash the resolver. In newdata(), the attacker-controlled nquestions count repeatedly passes DNS names to skip_name(), which traverses label lengths without checking the UDP packet boundary and returns an out-of-range pointer that is read as a dns_answer structure. Unauthenticated local-segment peers can reach mDNS builds on UDP 5353 without an outstanding query; standard DNS builds require injection from UDP port 53 during an outstanding query.

CVSS severity7.1
High
EPSS probability0.25%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in the Contiki-NG DNS/mDNS resolver allows attackers to disclose memory or crash the resolver. In newdata(), the attacker-controlled nquestions count repeatedly passes DNS names to skip_name(), which traverses label lengths without checking the UDP packet boundary and returns an out-of-range pointer that is read as a dns_answer structure. Unauthenticated local-segment peers can reach mDNS builds on UDP 5353 without an outstanding query; standard DNS builds require injection from UDP port 53 during an outstanding query.

The record

CVE
CVE-2026-5856
Published
Aug 6, 2026
Updated
Aug 6, 2026
Vendor
Contiki-NG
Product
Contiki-NG
Classifications
CWE-125, T1499.004
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 6, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 6, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

Contiki-NG · Contiki-NGversion=0 <04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe

Published CVSS scores

7.1VulnCheckCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L
7.1VulnCheckCVSS:4.0/AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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