CVE-2026-5856 Contiki-NG CVE debrief

Who should care

Organizations using Contiki-NG's DNS/mDNS resolver should be aware of this vulnerability and take immediate action to mitigate the risk. This includes verifying and applying patches or updates, implementing network segmentation and isolation, monitoring DNS traffic, and conducting regular vulnerability assessments and penetration testing.

Technical summary

The Contiki-NG DNS/mDNS resolver skip_name() function in os/services/resolv/resolv.c is vulnerable to an out-of-bounds read attack. The function 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. This vulnerability allows an attacker to trigger an out-of-bounds read of uip_buf and adjacent memory, disclosing memory contents or crashing the resolver. Organizations should verify and apply patches or updates, implement network segmentation and isolation, monitor DNS traffic, and conduct regular vulnerability assessments and penetration testing to mitigate the risk. The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected products. However, the source detail is limited, and further verification is required to determine the full scope of the vulnerability. To address this vulnerability, it is essential to understand the impact of the out-of-bounds read attack and take immediate action to prevent exploitation. This includes reviewing the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance, planning vendor-supported updates or mitigations through normal change control where exposure is confirmed, and reviewing compensating controls for exposed systems while remediation is scheduled and verified. Additionally, checking relevant monitoring, detection, and logs for exposed assets that need extra review and tracking exceptions, retesting remediated assets, and closing the item only after evidence is documented are crucial steps in addressing this vulnerability. The vulnerability affects Contiki-NG's DNS/mDNS resolver, and its exploitation can lead to memory disclosure or crashes. Therefore, it is crucial for organizations to prioritize patching and mitigation efforts to prevent potential attacks. By understanding the vulnerability and taking proactive measures, organizations can reduce the risk of exploitation and protect their systems from potential attacks. The Contiki-NG DNS/mDNS resolver skip_name

Defensive priority

High-priority defensive actions are required to address the out-of-bounds read vulnerability in Contiki-NG's DNS/mDNS resolver.

Recommended defensive actions

• Verify and apply the available patches or updates to the Contiki-NG DNS/mDNS resolver
• Implement network segmentation and isolation to limit the attack surface
• Monitor DNS traffic and implement rate limiting to prevent exploitation
• Conduct regular vulnerability assessments and penetration testing to identify potential weaknesses
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, including its description, CVSS score, and affected products. However, the source detail is limited, and further verification is required to determine the full scope of the vulnerability.

Official resources