CVE-2025-59024: DNS Recursor Cache Poisoning DoS Flaw

CVE-2025-59024 Overview

CVE-2025-59024 is a DNS cache poisoning vulnerability affecting PowerDNS Recursor. The vulnerability allows attackers to inject malicious data into the DNS resolver's cache through specially crafted delegation responses or fragmented IP packets. This cache poisoning attack can redirect users to attacker-controlled infrastructure, enabling phishing campaigns, malware distribution, or interception of sensitive traffic.

Critical Impact

Attackers can poison DNS cache delegations through crafted network packets, potentially redirecting legitimate traffic to malicious destinations without user awareness.

Affected Products

• PowerDNS Recursor (specific versions detailed in security advisory)

Discovery Timeline

• 2026-02-09 - CVE CVE-2025-59024 published to NVD
• 2026-02-09 - Last updated in NVD database

Technical Details for CVE-2025-59024

Vulnerability Analysis

This vulnerability exploits weaknesses in how PowerDNS Recursor processes and caches DNS delegation responses. DNS resolvers rely on delegation records to navigate the hierarchical DNS structure, trusting responses from authoritative servers to direct queries to the appropriate nameservers. The flaw allows attackers to inject poisoned delegation data into the resolver's cache, causing subsequent queries to be directed to attacker-controlled nameservers.

The attack can be executed through two vectors: crafted delegation responses that exploit insufficient validation in the delegation handling code, or through IP fragmentation attacks that allow attackers to manipulate response content before it reaches the resolver. When successful, the poisoned cache entries persist according to the TTL (Time-To-Live) values specified by the attacker, potentially affecting all clients relying on the compromised resolver.

Root Cause

The root cause lies in insufficient validation of delegation responses and inadequate protection against IP fragmentation-based attacks. The Recursor fails to properly verify the authenticity and integrity of certain delegation records, allowing malicious data to be cached. Additionally, the handling of fragmented IP packets does not adequately prevent attackers from injecting malicious content into reassembled DNS responses.

Attack Vector

The attack is network-based and does not require authentication or user interaction. An attacker positioned to send packets to the target resolver can exploit this vulnerability by:

1. Crafting malicious DNS delegation responses that appear legitimate to the resolver
2. Using IP fragmentation techniques to inject malicious content into DNS response packets
3. Timing the attack to coincide with legitimate DNS queries to increase success probability

The attacker must be able to send UDP packets that reach the resolver, either from the internet for public resolvers or from within the network for internal resolvers. The attack primarily impacts data integrity by allowing cache poisoning, with potential for limited availability impact.

The vulnerability mechanism involves manipulating DNS delegation records that direct the resolver to malicious nameservers. For detailed technical information, see the PowerDNS Security Advisory 2025-06.

Detection Methods for CVE-2025-59024

Indicators of Compromise

• Unexpected changes in DNS resolution patterns, particularly for well-known domains
• DNS cache entries pointing to unusual or unknown nameservers
• Increased volume of DNS queries from the resolver to unfamiliar IP addresses
• Anomalous delegation chains in DNS debug logs

Detection Strategies

• Monitor DNS resolver logs for unexpected delegation record changes
• Implement DNSSEC validation to detect tampered DNS responses
• Deploy network monitoring to identify suspicious fragmented UDP traffic targeting DNS resolvers
• Compare DNS resolution results across multiple resolvers to detect inconsistencies

Monitoring Recommendations

• Enable verbose logging on PowerDNS Recursor to capture delegation handling events
• Set up alerting for DNS cache modifications involving critical domains
• Monitor resolver response latency for anomalies that may indicate cache manipulation
• Track outbound DNS query patterns for connections to newly observed nameservers

How to Mitigate CVE-2025-59024

Immediate Actions Required

• Apply the security patch from PowerDNS as outlined in the security advisory
• Enable DNSSEC validation on the Recursor to reject unsigned or improperly signed responses
• Review and restrict network access to the DNS resolver to trusted sources only
• Flush the DNS cache after applying patches to remove any potentially poisoned entries

Patch Information

PowerDNS has released security updates to address this vulnerability. Administrators should consult the PowerDNS Security Advisory 2025-06 for specific patch versions and update instructions. Apply the patch immediately to all affected PowerDNS Recursor installations.

Workarounds

• Enable DNSSEC validation (dnssec=validate) to cryptographically verify DNS responses
• Implement firewall rules to block IP fragments targeting UDP port 53
• Reduce cache TTL values to limit the duration of any successful poisoning
• Deploy Response Rate Limiting (RRL) to mitigate attack amplification

# Configuration example for PowerDNS Recursor hardening
# Enable DNSSEC validation
dnssec=validate

# Reduce maximum cache TTL to limit poisoning impact
max-cache-ttl=3600

# Enable logging for security monitoring
quiet=no
log-common-errors=yes