CVE-2025-30193 is a high-severity vulnerability affecting PowerDNS DNSdist, a DNS load balancer and proxy widely used to manage and secure DNS traffic. The vulnerability arises from uncontrolled recursion in the handling of TCP connections when DNSdist is configured to allow an unlimited number of queries on a single incoming TCP connection. An attacker can exploit this by crafting a malicious TCP exchange that triggers excessive recursive calls, leading to stack exhaustion and ultimately causing the DNSdist process to crash. This results in a denial of service (DoS) condition, disrupting DNS resolution services dependent on DNSdist. The vulnerability is classified under CWE-674 (Uncontrolled Recursion), indicating that the recursive logic lacks proper bounds checking or termination conditions. The CVSS v3.1 base score is 7.5, reflecting a high impact primarily on availability, with no impact on confidentiality or integrity. The attack vector is network-based (AV:N), requires no privileges (PR:N), no user interaction (UI:N), and affects the system scope (S:U). The vulnerability does not require authentication and can be triggered remotely by any attacker capable of establishing a TCP connection to the vulnerable DNSdist instance. The recommended remediation is to upgrade to DNSdist version 1.9.10 or later, where the issue is patched. As a workaround, administrators can limit the maximum number of queries per TCP connection using the setMaxTCPQueriesPerConnection setting to a safe threshold (e.g., 50), thereby preventing excessive recursion and stack exhaustion. No known exploits are reported in the wild as of the publication date.

For European organizations, the impact of this vulnerability can be significant, especially for those relying on PowerDNS DNSdist for DNS traffic management and load balancing. A successful exploitation leads to denial of service, causing DNS resolution failures that can disrupt internal and external network communications, impacting business operations, customer-facing services, and critical infrastructure. This can affect availability of web services, email, and other DNS-dependent applications. Given the central role of DNS in network operations, the DoS could cascade into broader operational disruptions. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure are particularly at risk due to their reliance on stable DNS services. The lack of confidentiality or integrity impact limits data breach concerns, but the availability impact alone can cause significant operational and reputational damage. Additionally, the ease of exploitation without authentication or user interaction increases the risk of opportunistic attacks or targeted disruption campaigns.

To mitigate this vulnerability effectively, European organizations should: 1) Immediately upgrade all DNSdist instances to version 1.9.10 or later, ensuring the patch is applied promptly. 2) If immediate upgrade is not feasible, configure the setMaxTCPQueriesPerConnection setting to a conservative limit such as 50 queries per TCP connection to prevent uncontrolled recursion and stack exhaustion. 3) Monitor DNSdist logs and network traffic for unusual patterns of TCP connections with excessive queries, which may indicate attempted exploitation. 4) Implement network-level protections such as rate limiting and connection throttling on DNSdist TCP ports to reduce the risk of abuse. 5) Conduct regular vulnerability assessments and penetration testing focused on DNS infrastructure to detect similar issues proactively. 6) Maintain an incident response plan that includes DNS service continuity measures, such as failover DNS servers or alternative DNS providers, to minimize downtime in case of an attack. 7) Educate network and security teams about this vulnerability and ensure timely communication of patches and configuration changes.