CVE-2017-15107 in Dnsmasq
Summary
by MITRE
A vulnerability was found in the implementation of DNSSEC in Dnsmasq up to and including 2.78. Wildcard synthesized NSEC records could be improperly interpreted to prove the non-existence of hostnames that actually exist.
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Analysis
by VulDB Data Team • 02/02/2023
The vulnerability identified as CVE-2017-15107 represents a critical flaw in the DNSSEC implementation within Dnsmasq versions 2.78 and earlier. This issue specifically targets the handling of wildcard synthesized NSEC records, which are fundamental components in DNS Security Extensions designed to provide authenticated denial of existence for DNS names. The flaw occurs when the DNS server processes wildcard records and incorrectly interprets the synthesized NSEC records, leading to a situation where the server fails to properly validate the existence of certain hostnames. This misinterpretation creates a security gap that could be exploited by malicious actors to bypass DNSSEC validation mechanisms. The vulnerability directly impacts the integrity of DNSSEC validation processes, potentially allowing attackers to craft DNS responses that appear legitimate while actually containing false information about hostname existence. This flaw falls under the category of DNS security misconfiguration and represents a failure in proper DNSSEC protocol implementation.
The technical nature of this vulnerability stems from how Dnsmasq handles wildcard expansion in DNSSEC environments. When a DNS query is made for a hostname that does not exist but falls under a wildcard domain, the server should generate synthesized NSEC records that properly demonstrate the non-existence of the queried name. However, in affected versions of Dnsmasq, the synthesized records are not correctly constructed or interpreted, creating opportunities for attackers to exploit the inconsistency. The flaw allows for a condition where the server might incorrectly prove that a hostname does not exist when it actually does, or conversely, fail to properly validate that a hostname exists when it should. This misinterpretation occurs at the DNSSEC validation layer where the server's internal logic for processing wildcard records conflicts with the expected DNSSEC behavior. The vulnerability is particularly dangerous because it operates at the core of DNS security validation mechanisms, potentially allowing for cache poisoning attacks or other DNS-based security breaches.
The operational impact of CVE-2017-15107 extends beyond simple DNS resolution issues, as it fundamentally undermines the security guarantees that DNSSEC is designed to provide. Organizations relying on Dnsmasq for DNS services with DNSSEC enabled face potential exposure to attacks that could compromise their DNS infrastructure. The vulnerability enables attackers to potentially bypass DNSSEC validation, which could lead to man-in-the-middle attacks, DNS cache poisoning, or other malicious activities that exploit the trust model of DNS resolution. This flaw particularly affects networks where DNSSEC is actively implemented and validated, as the incorrect handling of wildcard records could allow adversaries to manipulate DNS responses in ways that would otherwise be prevented by proper DNSSEC validation. The impact is especially severe in environments where DNS security is critical, such as enterprise networks, internet service providers, or any infrastructure that depends on authenticated DNS resolution.
Mitigation strategies for this vulnerability require immediate action to upgrade Dnsmasq to versions 2.79 or later, where the DNSSEC implementation has been corrected to properly handle wildcard synthesized NSEC records. System administrators should also consider implementing additional monitoring for anomalous DNS behavior that might indicate exploitation attempts. The fix addresses the core issue by ensuring that wildcard records are properly generated and validated according to DNSSEC standards, specifically resolving the incorrect interpretation of synthesized NSEC records. Organizations should also review their DNSSEC configurations and ensure that proper validation procedures are in place. This vulnerability aligns with CWE-254 in the Common Weakness Enumeration, which covers security weaknesses related to improper handling of security features, and maps to ATT&CK technique T1071.004 for DNS tunneling and T1496 for resource hijacking through DNS manipulation. Regular security audits of DNS infrastructure and monitoring for DNSSEC validation failures should be implemented as part of ongoing security practices to prevent similar issues from arising in other DNS implementations.