CVE-2024-1737: BIND 9 DNS Performance DoS Vulnerability

CVE-2024-1737 Overview

CVE-2024-1737 is a resource exhaustion vulnerability affecting ISC BIND 9, one of the most widely deployed DNS server implementations. The vulnerability occurs in resolver caches and authoritative zone databases when handling hostnames with significant numbers of Resource Records (RRs). When a hostname accumulates large numbers of RRs of any record type (RTYPE), the DNS server experiences degraded performance during content addition, updates, and client query handling operations.

This weakness (CWE-770: Allocation of Resources Without Limits or Throttling) can be exploited remotely over the network without requiring any authentication or user interaction, potentially causing denial of service conditions on affected DNS infrastructure.

Critical Impact

Attackers can remotely degrade DNS server performance by exploiting RRset management inefficiencies, potentially causing service disruption for organizations relying on affected BIND 9 installations.

Affected Products

• BIND 9 versions 9.11.0 through 9.11.37
• BIND 9 versions 9.16.0 through 9.16.50
• BIND 9 versions 9.18.0 through 9.18.27
• BIND 9 versions 9.19.0 through 9.19.24
• BIND 9 Supported Preview Edition 9.11.4-S1 through 9.11.37-S1
• BIND 9 Supported Preview Edition 9.16.8-S1 through 9.16.50-S1
• BIND 9 Supported Preview Edition 9.18.11-S1 through 9.18.27-S1

Discovery Timeline

• 2024-07-23 - CVE-2024-1737 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-1737

Vulnerability Analysis

This vulnerability stems from how BIND 9 handles Resource Record sets (RRsets) for individual hostnames. When a single hostname accumulates a large number of Resource Records—regardless of record type—the internal data structures used by BIND's resolver cache or authoritative zone database become inefficient to process.

The performance degradation manifests in two primary scenarios: during content updates (when new RRs are added or existing ones modified) and when processing client DNS queries for hostnames with large RRsets. This behavior can be triggered remotely by an attacker who crafts DNS responses or zone data containing excessive RRs for targeted hostnames.

The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that BIND fails to properly constrain the resources consumed when managing large RRsets, leading to computational overhead that degrades overall server performance.

Root Cause

The root cause lies in BIND 9's internal algorithms for managing RRset data structures. When processing hostnames with unusually large numbers of associated Resource Records, the time complexity of operations such as insertion, update, and lookup increases significantly. The lack of effective limits on RRset sizes allows attackers to force the server into computationally expensive operations, consuming CPU cycles and memory resources that should be available for legitimate DNS query processing.

Attack Vector

The vulnerability is exploitable via network-based attacks targeting BIND 9 DNS servers. An attacker can exploit this vulnerability by:

1. Cache Poisoning Preparation: Sending crafted DNS responses that populate the resolver cache with hostnames containing excessive RRs
2. Zone Transfer Exploitation: If zone transfers are permitted, uploading zone data with hostnames containing large RRsets
3. Recursive Query Abuse: Triggering the resolver to cache responses from malicious authoritative servers that return oversized RRsets

The attack requires no authentication and no user interaction, making it particularly dangerous for internet-facing DNS infrastructure.

The vulnerability allows remote attackers to degrade DNS server performance by exploiting the RRset management algorithm. When a hostname with an excessive number of Resource Records is queried or updated, the server's internal data structure operations become computationally expensive. This can be achieved through crafted DNS responses that poison the resolver cache with hostnames containing numerous RRs. For detailed technical analysis and proof-of-concept scenarios, refer to the ISC CVE-2024-1737 Details advisory.

Detection Methods for CVE-2024-1737

Indicators of Compromise

• Unusual CPU utilization spikes on BIND 9 DNS servers during query processing
• Increased DNS query response latency for specific hostnames
• Memory consumption growth in named process without corresponding traffic increase
• DNS server logs indicating slow query processing or timeout warnings

Detection Strategies

• Monitor BIND 9 server performance metrics for anomalous CPU and memory usage patterns
• Implement DNS query logging and analyze for hostnames with unusually large response sizes
• Configure threshold-based alerting for DNS query latency exceeding normal baselines
• Review resolver cache statistics for hostnames accumulating abnormal RRset counts

Monitoring Recommendations

• Deploy network monitoring to detect DNS responses containing excessive Resource Records
• Utilize BIND's built-in statistics channels to track RRset sizes and cache performance
• Implement DNS traffic analysis to identify potential cache poisoning attempts
• Configure SentinelOne Singularity platform to monitor named process behavior for resource exhaustion indicators

How to Mitigate CVE-2024-1737

Immediate Actions Required

• Upgrade BIND 9 to the latest patched version addressing CVE-2024-1737
• Review DNS server configurations for unnecessary exposure to untrusted networks
• Implement rate limiting on DNS queries to reduce attack surface
• Consider deploying DNS firewalls or response policy zones (RPZ) to filter malicious responses

Patch Information

ISC has released security updates addressing this vulnerability. Administrators should upgrade to patched versions as documented in the ISC CVE-2024-1737 Details advisory. Additionally, ISC provides guidance on implementing RRset limits in the ISC RRSET Limits Guidance documentation.

Organizations running BIND 9 on NetApp systems should also consult the NetApp Security Advisory NTAP-20240731-0003 for platform-specific guidance.

Workarounds

• Implement RRset size limits as described in ISC's RRSET limits guidance documentation
• Configure response rate limiting (RRL) to mitigate the impact of cache poisoning attempts
• Restrict zone transfers to authorized secondary servers only
• Consider deploying upstream DNS filtering to block responses with abnormal RRset sizes

# Configuration example - Enable Response Rate Limiting in BIND 9
# Add to named.conf options block
options {
    rate-limit {
        responses-per-second 10;
        window 5;
        slip 2;
        log-only no;
    };
};