CVE-2026-27831 identifies a heap-based out-of-bounds read vulnerability in rldns, an open source DNS server developed by bluedragonsecurity. The affected version is 1.3, where improper bounds checking allows the server to read memory beyond allocated buffers. This flaw can be triggered remotely without any authentication or user interaction, making it easily exploitable over the network. The consequence of this vulnerability is a denial of service (DoS) condition, as the out-of-bounds read can cause the DNS server process to crash or behave unpredictably, disrupting DNS resolution services. The vulnerability is categorized under CWE-125, which involves reading memory outside the intended buffer boundaries. The vendor addressed this issue in version 1.4 by applying a patch that corrects the bounds checking logic. The CVSS v3.1 base score is 7.5, reflecting high severity due to network attack vector, no required privileges or user interaction, and a significant impact on availability. No known exploits have been reported in the wild as of the publication date. The vulnerability does not affect confidentiality or integrity, but the availability impact on DNS services can have cascading effects on dependent systems and networks.

The primary impact of CVE-2026-27831 is denial of service against DNS infrastructure running rldns version 1.3. Organizations relying on this DNS server may experience service outages, leading to disruption of domain name resolution critical for internal and external communications. This can affect web services, email delivery, and other network-dependent applications. The ease of remote exploitation without authentication increases the risk of widespread attacks, potentially leveraged by attackers to cause network instability or as part of larger distributed denial of service (DDoS) campaigns. While confidentiality and integrity are not directly compromised, the unavailability of DNS services can indirectly impact business operations, customer trust, and compliance with service level agreements. Critical infrastructure providers, cloud service operators, and enterprises using rldns in their DNS stack are particularly vulnerable to operational disruptions.

Organizations should immediately upgrade rldns from version 1.3 to version 1.4 or later, where the vulnerability is patched. If upgrading is not immediately feasible, network-level mitigations such as restricting access to the DNS server from untrusted sources using firewalls or access control lists can reduce exposure. Implementing DNS redundancy with alternative DNS servers can minimize service disruption during an attack. Monitoring DNS server logs and network traffic for unusual patterns or crashes can help detect exploitation attempts early. Additionally, applying runtime protections such as memory safety tools or sandboxing the DNS server process may reduce the impact of out-of-bounds reads. Regularly auditing and updating DNS software and dependencies is critical to maintaining security posture.