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CVE-2025-30193: Denial of Service Vulnerability in DNSdist

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Overview

This report provides a detailed analysis of a critical vulnerability, CVE-2025-30193, in DNSdist. DNSdist is a highly DNS, DoS and abuse aware load balancer. This vulnerability affects all systems running unpatched versions of DNSdist and has significant implications, including the potential for system compromise or data leakage. It is vital for all users to understand the risks associated with this vulnerability and apply the necessary mitigation strategies.

Vulnerability Summary

CVE ID: CVE-2025-30193
Severity: High (CVSS: 7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage

Affected Products

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Product | Affected Versions

DNSdist | All versions before 1.9.10

How the Exploit Works

The vulnerability arises when DNSdist is configured to allow an unlimited number of queries on a single, incoming TCP connection from a client. In such scenarios, an attacker can craft a TCP exchange that triggers an exhaustion of the stack and a subsequent crash of DNSdist. This crash results in a denial of service, which can potentially lead to system compromise or data leakage.

Conceptual Example Code

A conceptual example of exploiting the vulnerability involves sending a large number of queries on a single TCP connection. This could hypothetically look like this:

for i in {1..1000000}
do
echo "query $i" | nc target.example.com 53
done

This bash script sends a million queries to the DNSdist server, which, if configured to allow an unlimited number of queries, could lead to stack exhaustion and a crash.

Remediation Steps

Users are advised to upgrade to the patched 1.9.10 version of DNSdist. In the event where an upgrade is not immediately possible, a workaround is to restrict the maximum number of queries on incoming TCP connections to a safe value, like 50, via the setMaxTCPQueriesPerConnection setting.
Additionally, deploying a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can serve as temporary mitigation.
We would like to thank Renaud Allard for bringing this issue to our attention.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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