CVE-2019-3807 in Recursor
Summary
by MITRE
An issue has been found in PowerDNS Recursor versions 4.1.x before 4.1.9 where records in the answer section of responses received from authoritative servers with the AA flag not set were not properly validated, allowing an attacker to bypass DNSSEC validation.
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Analysis
by VulDB Data Team • 07/04/2023
The vulnerability identified as CVE-2019-3807 represents a critical flaw in PowerDNS Recursor's DNSSEC validation mechanism that undermines the security assurances provided by DNS security extensions. This issue affects versions 4.1.x prior to 4.1.9 and specifically targets the validation process of DNS records received from authoritative servers. The flaw occurs when the recursor encounters DNS responses where the authoritative answer (AA) flag is not set, which should typically indicate that the server is authoritative for the queried domain. This condition creates a validation gap that allows malicious actors to exploit the system's trust model.
The technical root cause of this vulnerability lies in the recursor's failure to properly validate DNS records when the AA flag is absent from responses received from authoritative servers. In normal DNSSEC operations, when a server responds with the AA flag set, it signals to the resolver that the response should be treated as authoritative and subject to stricter validation checks. However, the PowerDNS Recursor implementation incorrectly bypasses critical validation steps when this flag is missing, even though the response may still contain records that should be verified for authenticity. This behavior creates a scenario where malicious actors can craft DNS responses that appear legitimate to the recursor while bypassing essential cryptographic validation mechanisms.
The operational impact of this vulnerability is severe as it allows attackers to perform DNS cache poisoning attacks that would normally be prevented by DNSSEC validation. An attacker can exploit this flaw by sending malicious DNS responses from non-authoritative servers that lack the AA flag, causing the recursor to accept forged records without proper validation. This creates a persistent threat where malicious DNS responses can be cached and served to legitimate clients, potentially redirecting traffic to malicious destinations or enabling man-in-the-middle attacks. The vulnerability effectively undermines the entire DNSSEC framework by allowing forged records to bypass validation when the AA flag is not present, which is a common scenario in certain network configurations and DNS server implementations.
This vulnerability maps to CWE-284 Access Control and CWE-312 Cleartext Storage of Sensitive Information within the Common Weakness Enumeration framework, as it represents a failure in access control mechanisms that allows unauthorized modification of DNS records. From the MITRE ATT&CK framework perspective, this vulnerability aligns with T1071.004 Application Layer Protocol DNS and T1566 Credential Access through Network Sniffing, as it enables attackers to manipulate DNS resolution results and potentially gain access to sensitive network resources. The flaw also relates to T1496 Resource Hijacking by allowing attackers to redirect network traffic through manipulated DNS responses.
Organizations should immediately upgrade to PowerDNS Recursor version 4.1.9 or later to address this vulnerability, as this release includes the necessary patches to properly validate DNS records regardless of the AA flag status. Network administrators should also implement additional monitoring of DNS traffic to detect anomalous responses that might indicate exploitation attempts. The mitigation strategy should include enabling strict DNSSEC validation settings, regularly auditing DNS cache contents, and implementing network segmentation to limit the potential impact of successful attacks. Organizations should also consider deploying DNS security monitoring tools that can detect and alert on suspicious DNS behavior patterns that may indicate exploitation of this vulnerability.