CVE-2019-3806 in Recursor
Summary
by MITRE
An issue has been found in PowerDNS Recursor versions after 4.1.3 before 4.1.9 where Lua hooks are not properly applied to queries received over TCP in some specific combination of settings, possibly bypassing security policies enforced using Lua.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/04/2023
The vulnerability identified as CVE-2019-3806 affects PowerDNS Recursor versions greater than 4.1.3 but prior to 4.1.9, representing a significant security flaw in DNS resolution infrastructure. This issue specifically impacts how the recursor handles Lua hooks when processing queries transmitted over the Transmission Control Protocol rather than the User Datagram Protocol. The flaw stems from improper implementation of security policies that rely on Lua scripting capabilities, creating potential bypass opportunities for malicious actors seeking to evade established security controls. The vulnerability demonstrates a critical gap in the application of security policies across different network transport protocols within the DNS resolution process.
The technical root cause of this vulnerability lies in the inconsistent handling of Lua hook execution contexts between TCP and UDP query processing pathways. When DNS queries are received over TCP connections, the recursor fails to properly invoke the configured Lua hooks that would normally enforce security policies, access controls, or query filtering mechanisms. This inconsistency creates a scenario where security policies implemented through Lua scripting remain effective for UDP queries but are effectively bypassed for TCP queries, potentially allowing malicious traffic to slip through without proper inspection or filtering. The flaw specifically manifests when certain configuration combinations are present, suggesting that the vulnerability is not universal but rather depends on specific operational settings within the PowerDNS Recursor deployment.
The operational impact of CVE-2019-3806 extends beyond simple policy bypass to potentially enable more sophisticated attack vectors against DNS infrastructure. Organizations relying on Lua-based security controls for DNS query filtering, access restriction, or malicious traffic detection may experience significant security degradation when TCP queries are processed without proper hook execution. Attackers could exploit this vulnerability to bypass domain blacklisting, query rate limiting, or other security measures that are properly enforced for UDP traffic but not for TCP connections. This creates a potential attack surface where malicious DNS queries can be processed without the intended security controls, potentially leading to data exfiltration, DNS tunneling, or other malicious activities that would normally be prevented by the configured Lua policies.
Security mitigations for CVE-2019-3806 primarily involve upgrading to PowerDNS Recursor version 4.1.9 or later, where the vulnerability has been addressed through proper implementation of Lua hook execution across all supported network protocols. Organizations should also conduct immediate assessments of their current DNS infrastructure to identify any configurations that might be susceptible to this vulnerability, particularly those utilizing Lua-based security policies. The remediation process should include comprehensive testing of DNS query handling across both TCP and UDP protocols to ensure that security policies are consistently applied regardless of transport method. Additionally, security teams should review their existing Lua hook configurations to understand the potential impact of the vulnerability and ensure that alternative security measures are in place to protect against the specific bypass scenarios that were possible before the fix was implemented.
This vulnerability aligns with CWE-691, which addresses insufficient control of code generation or execution, and relates to ATT&CK technique T1071.004 for Application Layer Protocol: DNS, as it affects the fundamental DNS resolution process and security controls that protect against malicious DNS activity. The issue demonstrates the importance of consistent security policy enforcement across all network protocol implementations within critical infrastructure components, highlighting the need for thorough testing and validation of security controls in multi-protocol environments. Organizations should treat this vulnerability as a reminder of the critical importance of maintaining up-to-date security software and conducting regular security assessments to identify potential gaps in protocol-specific security implementations.