Is CVE-2026-5856 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-5856 being exploited in the wild.

How severe is CVE-2026-5856?

High severity, with a CVSS score of 7.1, published 6 August 2026.

Which products and versions are affected?

Contiki-NG prior to commit 04a3f0a (2026-07-08).

Is there a fix for CVE-2026-5856?

A patch was published on 2026-07-08: Merge of bounds-checking fix in commit 04a3f0a Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-5856 attacked?

It is attacked over the network or from the adjacent network, in an operating system.

Am I affected by CVE-2026-5856?

Check whether you run Contiki-NG at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-5856: Contiki-NG DNS resolver out-of-bounds read in skip_name()

CVE-2026-5856 · Severity: high · CVSS 7.1 · Published 2026-08-06

Contiki-NG is an operating system for IoT devices that includes a DNS and multicast DNS resolver. A bug in the DNS name parsing logic fails to validate packet boundaries before reading DNS wire-format labels, allowing an attacker to read memory beyond the packet buffer. On multicast DNS configurations, any local network peer can trigger this without authentication; on standard DNS, an attacker injecting forged DNS responses can exploit it. This can disclose sensitive memory contents or crash the resolver, disrupting network connectivity.

Technologies: Contiki-NG. Vendors: Contiki-NG.

Quick answers

Is CVE-2026-5856 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-5856 being exploited in the wild.
How severe is CVE-2026-5856?: High severity, with a CVSS score of 7.1, published 6 August 2026.
Which products and versions are affected?: Contiki-NG prior to commit 04a3f0a (2026-07-08).
Is there a fix for CVE-2026-5856?: A patch was published on 2026-07-08: Merge of bounds-checking fix in commit 04a3f0a Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-5856 attacked?: It is attacked over the network or from the adjacent network, in an operating system.
Am I affected by CVE-2026-5856?: Check whether you run Contiki-NG at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is a missing bounds check in the skip_name() function in os/services/resolv/resolv.c. The DNS name parsing code walks DNS wire-format name labels without validating that the pointer remains within the packet buffer, and the caller newdata() invokes skip_name() in a loop nquestions times based on an attacker-controlled DNS header field before validating the transaction ID. When nquestions exceeds the number of complete questions present, skip_name() reads past the UDP packet buffer (uip_buf), and the out-of-bounds pointer is cast to struct dns_answer * for further reads. On MDNS-enabled builds, any peer on the local network segment can trigger this via multicast UDP 5353 without an outstanding query; standard DNS builds require an attacker who can inject UDP responses from port 53 during an outstanding query. Impact includes out-of-bounds memory reads disclosing uip_buf and adjacent memory, or denial of service via resolver crash. A fix adding proper bounds checking was committed on 2026-07-08.

Affected products

Contiki-NG Contiki-NG prior to commit 04a3f0a (2026-07-08)

Timeline

2026-08-06: disclosed
2026-07-08: patched: Merge of bounds-checking fix in commit 04a3f0a

References

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