CVE-2006-4252 in Recursor
Summary
by MITRE
PowerDNS Recursor 3.1.3 and earlier allows remote attackers to cause a denial of service (resource exhaustion and application crash) via a CNAME record with a zero TTL, which triggers an infinite loop.
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Analysis
by VulDB Data Team • 04/27/2026
The vulnerability identified as CVE-2006-4252 affects PowerDNS Recursor versions 3.1.3 and earlier, presenting a critical denial of service risk that can be exploited by remote attackers to disrupt network services. This flaw specifically targets the recursive DNS resolution process where the application fails to properly handle certain CNAME record configurations, creating a condition that leads to resource exhaustion and eventual application crash. The vulnerability stems from improper validation of DNS record attributes, particularly the Time To Live value associated with CNAME records.
The technical implementation of this vulnerability involves a specific edge case in DNS record processing where a CNAME record with a zero TTL value triggers an infinite loop within the PowerDNS Recursor's internal processing logic. When the resolver encounters such a malformed record, it enters a recursive processing cycle that consumes excessive system resources including CPU cycles and memory allocation. This infinite loop occurs because the application's state machine does not properly validate the TTL value of CNAME records before proceeding with recursive resolution operations. The flaw represents a classic example of inadequate input validation and error handling in network service applications, falling under CWE-129 Input Validation and CWE-691 Uncontrolled Resource Consumption.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability of DNS services across affected networks. When exploited, the infinite loop causes the PowerDNS Recursor to consume all available system resources, leading to complete application crash and denial of service for legitimate DNS queries. This makes the vulnerability particularly dangerous in environments where DNS resolution is critical for network operations, as it can cascade into broader service outages affecting multiple dependent systems. The remote exploitation aspect means that attackers need not be physically present on the network to cause damage, making it a significant threat to network availability.
Organizations affected by this vulnerability should prioritize immediate patching of PowerDNS Recursor installations to version 3.1.4 or later, which contains the necessary fixes to properly handle CNAME records with zero TTL values. Additionally, network administrators should implement monitoring solutions to detect unusual resource consumption patterns that might indicate exploitation attempts. The fix implemented by PowerDNS developers addresses the root cause by adding proper validation of TTL values in CNAME records before initiating recursive processing, preventing the infinite loop condition. This remediation aligns with ATT&CK technique T1499.004 for resource exhaustion attacks and demonstrates the importance of proper input validation in preventing denial of service conditions. Network security teams should also consider implementing rate limiting and connection monitoring as additional defensive measures to mitigate potential exploitation attempts.