CVE-2019-10190 in Resolver
Summary
by MITRE
A vulnerability was discovered in DNS resolver component of knot resolver through version 3.2.0 before 4.1.0 which allows remote attackers to bypass DNSSEC validation for non-existence answer. NXDOMAIN answer would get passed through to the client even if its DNSSEC validation failed, instead of sending a SERVFAIL packet. Caching is not affected by this particular bug but see CVE-2019-10191.
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Analysis
by VulDB Data Team • 10/02/2024
The vulnerability identified as CVE-2019-10190 affects the knot resolver DNS implementation, specifically targeting the DNSSEC validation mechanism within the resolver component. This flaw exists in versions prior to 4.1.0, with the most critical impact occurring between versions 3.2.0 and 4.0.9. The issue represents a significant security weakness in the DNS infrastructure that undermines the integrity of DNSSEC validation processes. The vulnerability operates at the core of DNS security protocols where the resolver should enforce strict validation of DNS responses before forwarding them to clients. When a DNS query results in a non-existent domain response, the resolver should validate the NXDOMAIN answer according to DNSSEC standards before accepting its legitimacy. However, this vulnerability allows malicious actors to exploit a gap in the validation logic that permits forged NXDOMAIN responses to be delivered to clients without proper DNSSEC verification.
The technical implementation flaw stems from how the knot resolver handles DNSSEC validation for non-existence proofs in DNS responses. In normal DNSSEC operation, when a query for a non-existent domain returns an NXDOMAIN response, the resolver must validate the cryptographic signatures and proof of non-existence according to RFC 4035 and related DNSSEC standards. The vulnerability creates a condition where failed DNSSEC validation of NXDOMAIN responses does not trigger the expected SERVFAIL error code that would inform clients of the validation failure. Instead, the malformed response gets passed through to the client, creating a false sense of security where clients receive responses that appear legitimate but may have been tampered with or forged by attackers. This behavior directly violates the fundamental principles of DNSSEC validation as defined by the Internet Engineering Task Force standards and represents a CWE-284 access control weakness in the validation mechanism.
The operational impact of this vulnerability extends beyond simple DNS resolution failures and creates substantial security implications for organizations relying on DNSSEC protection. Attackers can exploit this weakness to perform cache poisoning attacks or manipulate DNS responses in ways that bypass security controls designed to prevent such interference. The vulnerability enables man-in-the-middle attacks where malicious actors can inject false NXDOMAIN responses for domains that should be protected by DNSSEC validation. This compromise affects the trust model of DNS resolution, potentially allowing attackers to redirect traffic or prevent access to legitimate services by exploiting the failure to properly validate DNSSEC signatures. Organizations using knot resolver versions affected by this vulnerability may experience cascading effects where downstream systems trust invalid DNS responses that appear to be legitimate due to the bypassed validation mechanism. The impact is particularly concerning for critical infrastructure and enterprise environments where DNSSEC validation is essential for maintaining secure network communications and preventing DNS-based attacks.
The mitigation strategy for CVE-2019-10190 requires immediate deployment of patched versions of knot resolver, specifically upgrading to version 4.1.0 or later where the validation logic has been corrected. System administrators should verify that all instances of knot resolver in their network infrastructure have been updated and that the DNSSEC validation mechanisms are functioning correctly. Additional monitoring should be implemented to detect any anomalies in DNS response behavior that might indicate exploitation attempts. The vulnerability also highlights the importance of proper DNSSEC implementation and the need for organizations to maintain updated DNS resolver software to prevent similar issues. This vulnerability aligns with ATT&CK technique T1071.004 for DNS tunneling and manipulation, where adversaries can exploit DNS infrastructure weaknesses to gain unauthorized access or manipulate network communications. Organizations should also consider implementing additional DNS security measures such as DNS firewalling, response policy zones, and comprehensive DNS monitoring to detect and prevent exploitation attempts. The fix addresses the core validation logic that ensures DNSSEC signatures are properly verified before accepting NXDOMAIN responses, thereby restoring the intended security properties of DNSSEC validation in the resolver component.