CVE-2009-3602 in Unbound
Summary
by MITRE
Unbound before 1.3.4 does not properly verify signatures for NSEC3 records, which allows remote attackers to cause secure delegations to be downgraded via DNS spoofing or other DNS-related attacks in conjunction with crafted delegation responses.
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Analysis
by VulDB Data Team • 08/23/2021
The vulnerability described in CVE-2009-3602 affects the Unbound DNS resolver version 1.3.4 and earlier, representing a critical flaw in DNS security verification mechanisms. This vulnerability specifically targets the handling of NSEC3 records within the DNS Security Extensions (DNSSEC) framework, which is designed to protect against various DNS-related attacks including cache poisoning and spoofing. The issue stems from insufficient signature verification processes that allow malicious actors to exploit weaknesses in the DNSSEC validation procedure.
The technical flaw manifests in the improper validation of NSEC3 record signatures within the Unbound resolver implementation. NSEC3 records are essential components of DNSSEC that provide authenticated denial of existence for DNS names, ensuring that when a queried name does not exist, the resolver can prove this fact through cryptographic signatures. When Unbound fails to properly verify these signatures, it creates an opening for attackers to manipulate DNS responses. The vulnerability enables attackers to craft malicious delegation responses that can trick the resolver into accepting invalid or spoofed DNS data, effectively bypassing the security guarantees that DNSSEC is meant to provide.
The operational impact of this vulnerability is severe and far-reaching within DNS infrastructure. Attackers can leverage this weakness to perform DNS spoofing attacks that downgrade secure delegations, potentially redirecting traffic to malicious servers or intercepting communications. This vulnerability particularly affects DNSSEC-protected zones where secure delegations are critical for maintaining the integrity of the DNS resolution process. The ability to downgrade secure delegations means that even zones that should be protected by DNSSEC can be compromised, undermining the entire trust model that DNSSEC establishes. This creates a cascading effect where the security benefits of DNSSEC are nullified, leaving networks vulnerable to man-in-the-middle attacks and other DNS-related threats.
The vulnerability aligns with several cybersecurity frameworks and attack patterns, including CWE-327 which addresses weak cryptographic algorithms and improper implementation of cryptographic protocols. It also maps to ATT&CK technique T1071.004 for DNS tunneling and T1566 for phishing, as the compromised DNS resolution can facilitate broader attack vectors. Organizations using Unbound versions prior to 1.3.4 face significant risk exposure, particularly those operating in environments where DNS security is critical for maintaining network integrity and preventing unauthorized access to resources.
Mitigation strategies for this vulnerability require immediate deployment of Unbound version 1.3.4 or later, which contains the necessary fixes for proper NSEC3 signature verification. System administrators should also implement additional monitoring of DNS resolution patterns to detect anomalous behavior that might indicate exploitation attempts. Network security teams should consider implementing DNS security measures beyond the basic resolver updates, including DNS firewalling, DNS query logging, and regular validation of DNSSEC signatures. Organizations should also review their DNS infrastructure configurations to ensure that DNSSEC validation is properly enabled and functioning correctly, as this vulnerability demonstrates how a single flaw in signature verification can compromise entire DNS resolution processes.