CVE-2016-7073 in PowerDNS
Summary
by MITRE
An issue has been found in PowerDNS before 3.4.11 and 4.0.2, and PowerDNS recursor before 4.0.4, allowing an attacker in position of man-in-the-middle to alter the content of an AXFR because of insufficient validation of TSIG signatures. A missing check of the TSIG time and fudge values was found in AXFRRetriever, leading to a possible replay attack.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2016-7073 represents a critical security flaw in PowerDNS software versions prior to 3.4.11 and 4.0.2, as well as PowerDNS recursor versions before 4.0.4. This issue stems from insufficient validation of TSIG (Transaction Signature) signatures during AXFR (Zone Transfer) operations, creating a significant vector for man-in-the-middle attacks that can compromise DNS zone integrity. The flaw specifically affects the AXFRRetriever component which is responsible for handling zone transfers between DNS servers, making it a core element in the DNS infrastructure that requires robust security controls.
The technical root cause of this vulnerability lies in the missing validation of TSIG time and fudge values within the AXFRRetriever module. TSIG signatures are designed to provide authentication and integrity protection for DNS transactions, but the implementation failed to properly verify time-related parameters that are crucial for preventing replay attacks. The fudge value in TSIG represents a time tolerance window that allows for minor time differences between communicating parties, but when this parameter is not properly validated, attackers can exploit the gap to replay old DNS records. This weakness directly maps to CWE-347, which addresses improper verification of cryptographic signatures, and specifically relates to the lack of proper time synchronization validation that should be part of any secure TSIG implementation.
The operational impact of this vulnerability is severe as it allows attackers positioned in man-in-the-middle positions to manipulate DNS zone data during transfer operations. When an attacker can successfully alter AXFR responses, they can inject malicious DNS records, redirect traffic to malicious servers, or cause service disruption by modifying authoritative zone information. This capability enables a range of attack vectors including DNS cache poisoning, traffic redirection, and potential compromise of downstream services that rely on the integrity of DNS zone data. The vulnerability essentially undermines the fundamental security assurances that TSIG signatures are meant to provide, making it particularly dangerous in environments where DNS integrity is critical for network security.
Organizations affected by this vulnerability should immediately upgrade to the patched versions of PowerDNS (3.4.11 and 4.0.2 for the authoritative server, and 4.0.4 for the recursor) to mitigate the risk of man-in-the-middle attacks and replay attacks on DNS zone transfers. Additional mitigations include implementing network-level security controls such as DNSSEC to provide additional layers of authentication and integrity protection beyond TSIG, monitoring DNS traffic for unusual AXFR patterns, and ensuring that all DNS servers maintain synchronized time through NTP services to prevent exploitation of time-related vulnerabilities. The ATT&CK framework categorizes this vulnerability under T1071.004 for DNS tunneling and T1566 for phishing, as attackers could leverage the compromised DNS data to redirect users to malicious sites or establish persistent access through manipulated DNS records. Security teams should also consider implementing network segmentation and access controls to limit the exposure of DNS servers to untrusted networks, as the vulnerability requires network-level access to exploit effectively.