CVE-2008-1637 in Recursor
Summary
by MITRE
PowerDNS Recursor before 3.1.5 uses insufficient randomness to calculate (1) TRXID values and (2) UDP source port numbers, which makes it easier for remote attackers to poison a DNS cache, related to (a) algorithmic deficiencies in rand and random functions in external libraries, (b) use of a 32-bit seed value, and (c) choice of the time of day as the sole seeding information.
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Analysis
by VulDB Data Team • 07/31/2021
The vulnerability described in CVE-2008-1637 affects PowerDNS Recursor versions prior to 3.1.5 and represents a significant security flaw in DNS cache poisoning resistance mechanisms. This issue stems from inadequate randomness in two critical components of the DNS resolver's operation: transaction ID (TRXID) generation and UDP source port number selection. The weakness creates predictable patterns that malicious actors can exploit to inject false DNS responses into the cache, potentially redirecting users to malicious websites or disrupting network services. The vulnerability directly impacts the fundamental security model of DNS resolution systems that rely on these randomized elements to prevent cache poisoning attacks.
The technical root cause of this vulnerability lies in the implementation of random number generation functions within the PowerDNS Recursor software. Specifically, the system utilizes external libraries that contain algorithmic deficiencies in their rand and random functions, which are designed to produce pseudorandom sequences that are insufficiently unpredictable for security purposes. The implementation uses only a 32-bit seed value for random number generation, which significantly reduces the entropy available for creating unpredictable sequences. Furthermore, the system relies exclusively on the time of day as the sole source of seeding information, creating a predictable pattern that attackers can easily reverse engineer or guess. This approach violates fundamental security principles for cryptographic randomness and makes the system vulnerable to statistical analysis and brute force attacks.
The operational impact of this vulnerability is severe as it enables remote attackers to perform DNS cache poisoning attacks with relatively low computational overhead. Attackers can exploit the predictable TRXID values and UDP source ports to craft malicious DNS responses that will be accepted by the vulnerable resolver and cached for subsequent queries. This allows for man-in-the-middle attacks where users are redirected to malicious domains, denial of service scenarios, or more sophisticated attack chains that leverage the compromised DNS cache for further exploitation. The vulnerability affects the integrity and authenticity of DNS resolution, which forms the backbone of internet connectivity and security infrastructure. Organizations relying on PowerDNS Recursor for DNS resolution are exposed to potential compromise of their network traffic and user data, making this a critical issue that requires immediate remediation.
Mitigation strategies for this vulnerability involve upgrading to PowerDNS Recursor version 3.1.5 or later, which addresses the insufficient randomness issues through improved random number generation algorithms and seeding mechanisms. System administrators should also implement additional security measures including DNSSEC deployment to provide cryptographic validation of DNS responses, monitoring for suspicious DNS traffic patterns, and network segmentation to limit the impact of potential cache poisoning attacks. The fix addresses the underlying CWE-330 weakness related to insufficient entropy in random number generation, which is categorized under the broader class of cryptographic weaknesses in the CWE taxonomy. Organizations should also consider implementing the ATT&CK framework's DNS tunneling and cache poisoning techniques to better understand and defend against these types of attacks. Regular security audits and penetration testing should verify that the updated system properly implements cryptographic randomness and that no other similar vulnerabilities exist in the DNS infrastructure stack.