CVE-2023-4408: Netapp Ontap DoS Vulnerability

CVE-2023-4408 Overview

CVE-2023-4408 is an algorithmic complexity vulnerability in the DNS message parsing code of ISC BIND's named daemon. The affected code section exhibits computational complexity that is overly high when processing certain types of DNS messages. While typical DNS traffic does not trigger the issue, specially crafted queries and responses can cause excessive CPU load on affected named instances, leading to a denial of service condition. This vulnerability impacts both authoritative DNS servers and recursive resolvers, making it a significant threat to DNS infrastructure.

Critical Impact

Attackers can exploit this vulnerability to cause excessive CPU consumption on BIND DNS servers through crafted DNS messages, potentially disrupting DNS resolution services for entire networks.

Affected Products

• ISC BIND 9.0.0 through 9.16.45, 9.18.0 through 9.18.21, 9.19.0 through 9.19.19
• ISC BIND Supported Preview Editions 9.9.3-S1 through 9.11.37-S1, 9.16.8-S1 through 9.16.45-S1, 9.18.11-S1 through 9.18.21-S1
• NetApp ONTAP 9.14.1 and 9.15.1
• Fedora 38 and 39

Discovery Timeline

• February 13, 2024 - CVE-2023-4408 published to NVD
• March 14, 2025 - Last updated in NVD database

Technical Details for CVE-2023-4408

Vulnerability Analysis

This vulnerability falls under CWE-407 (Inefficient Algorithmic Complexity), a class of weaknesses where an algorithm's computational complexity allows attackers to consume disproportionate resources relative to input size. In the context of BIND's DNS message parsing, the vulnerable code section processes certain DNS message structures with an algorithmic complexity that can be exploited.

The DNS protocol allows for complex message structures including multiple questions, answers, authority records, and additional records. The parsing routine in named handles these structures with computational overhead that becomes problematic when messages are specifically crafted to maximize processing time. An attacker does not need authentication or special privileges to exploit this vulnerability—they simply need network access to send DNS queries to an affected server.

Root Cause

The root cause lies in the DNS message parsing implementation within named. The code section responsible for parsing DNS messages uses an algorithm with computational complexity that scales poorly with certain message characteristics. When processing maliciously crafted DNS queries or responses, the parsing routine enters code paths that consume excessive CPU cycles, starving other DNS operations and potentially rendering the service unavailable.

Attack Vector

This is a network-based attack that can be executed remotely without authentication. The attack vector involves sending specially crafted DNS messages to an affected BIND server. The vulnerability affects both authoritative servers (which receive queries from resolvers) and recursive resolvers (which receive queries from clients and responses from other servers). This dual exposure significantly increases the attack surface.

An attacker can craft DNS queries designed to trigger the inefficient parsing code paths. When the named process receives and attempts to parse these messages, CPU utilization spikes dramatically. Sustained attacks can exhaust CPU resources, causing legitimate DNS queries to time out and effectively denying service to users relying on the affected DNS infrastructure.

Detection Methods for CVE-2023-4408

Indicators of Compromise

• Unusual spikes in CPU utilization on DNS servers running BIND
• Increased DNS query response times or timeouts reported by clients
• Abnormal DNS traffic patterns with malformed or unusually structured queries
• System logs showing high resource consumption by the named process

Detection Strategies

• Monitor CPU utilization on BIND DNS servers and alert on sustained high usage above baseline thresholds
• Implement network-based detection for DNS queries with abnormal record counts or unusual structure patterns
• Enable BIND query logging and analyze for repeated queries from single sources that correlate with performance degradation
• Use DNS traffic analysis tools to identify potential algorithmic complexity attack patterns

Monitoring Recommendations

• Configure resource monitoring dashboards to track named process CPU and memory consumption in real-time
• Establish baseline DNS query response times and alert when latency exceeds normal parameters
• Implement rate limiting and query pattern analysis at network perimeter devices
• Review BIND server logs regularly for signs of exploitation attempts or service degradation

How to Mitigate CVE-2023-4408

Immediate Actions Required

• Upgrade BIND to patched versions: 9.16.48, 9.18.24, or 9.19.21 (or later) for standard editions
• For Supported Preview Editions, upgrade to 9.16.48-S1 or 9.18.24-S1 (or later)
• Review DNS server exposure and restrict access where possible using firewall rules
• Implement DNS query rate limiting to reduce the impact of exploitation attempts

Patch Information

ISC has released patched versions of BIND that address this vulnerability. Organizations should consult the ISC CVE-2023-4408 Documentation for specific upgrade guidance and version availability. Additionally, vendor-specific patches are available from Fedora through their package management system and from NetApp via their Security Advisory. The Openwall oss-security Announcement provides additional technical context on the vulnerability disclosure.

Workarounds

• Implement strict rate limiting on DNS queries to reduce the impact of malicious traffic
• Deploy DNS traffic filtering at network boundaries to block anomalous query patterns
• Consider using DNS load balancers or anycast to distribute query load across multiple servers
• Restrict recursive resolver access to trusted client networks only

# Example: Configure rate limiting in BIND named.conf
# Add to options section to limit query rates
options {
    rate-limit {
        responses-per-second 10;
        window 5;
    };
};