Contiki-NG: Out-of-bounds Read
CVE-2026-5856 is a high-severity out-of-bounds read vulnerability in Contiki-NG, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. The record lists version 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe as the first without the flaw, so updating Contiki-NG to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Contiki-NG to 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Contiki-NG | Contiki-NG | before 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe | 04a3f0a0067d2ee87d1f297b6d0f4392d8c98ffe |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- AdjacentThe attacker must be on the same local network segment.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- LowPerformance or availability is reduced.
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:L. Scored by CNA (vulncheck.com).
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.1 | High | CNA (vulncheck.com) |
| CVSS 3.1 | 7.1 | High | CNA (vulncheck.com) |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
How developers prevent this class of flaw
- Use a language that provides appropriate memory abstractions.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Other vulnerabilities in Contiki-NG
- 8.1 High severity
- 7.5 High severity
- 7.5 High severity
- 9.6 Critical severity
- 9.6 Critical severity
- 7.5 High severity
Recent Out-of-bounds Read vulnerabilities
- 7.1 High severity
- 8.1 High severity
- 7.8 High severity
- 7.8 High severity
- 9.8 Critical severity
- 7.8 High severity
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