CVE-2023-50387: Red Hat Enterprise Linux DNS DoS Attack

CVE-2023-50387 Overview

Certain DNSSEC aspects of the DNS protocol (in RFC 4033, 4034, 4035, 6840, and related RFCs) allow remote attackers to cause a denial of service (CPU consumption) via one or more DNSSEC responses, aka the "KeyTrap" issue.

Critical Impact
This vulnerability can lead attackers to exhaust CPU resources, causing a denial of service remotely exploitable over the network.

Affected Products

Redhat Enterprise Linux
Microsoft Windows Server
ISC BIND

Discovery Timeline

Not Available - Vulnerability discovered by Not Available
Not Available - Responsible disclosure to redhat
Not Available - CVE CVE-2023-50387 assigned
Not Available - redhat releases security patch
2024-02-14 - CVE CVE-2023-50387 published to NVD
2025-11-04 - Last updated in NVD database

Technical Details for CVE-2023-50387

Vulnerability Analysis

The "KeyTrap" issue arises from certain DNSSEC protocol requirements which demand the evaluation of all combinations of DNSKEY and RRSIG records associated with a zone. This results in excessive CPU resource consumption.

Root Cause

The root cause lies in the DNS protocol specification's need to handle numerous DNSKEY and RRSIG records for zone validation, which becomes computationally expensive.

Attack Vector

This vulnerability can be exploited remotely over the network by manipulating DNSSEC responses.

// Example exploitation code (sanitized)
#include <stdio.h>
#include <stdlib.h>

int main() {
    // Mock DNSSEC responses to trigger resource exhaustion
    char dnssec_response[10000];
    int i;
    for (i = 0; i < 10000; i++) {
        dnssec_response[i] = 'A';  // Fill with data
    }
    printf("Crafted DNSSEC response to induce high CPU usage.\n");
    return 0;
}

Detection Methods for CVE-2023-50387

Indicators of Compromise

Unusual spikes in CPU consumption
Excessive logs from DNSSEC validating resolver
Slow response times from DNS server

Detection Strategies

Monitor CPU usage patterns and traffic flow metrics that could indicate anomalous behavior triggered by DNSSEC validation processes.

Monitoring Recommendations

Implement continuous monitoring for DNS services to identify unusual patterns and resource constraints that signal potential exploitation.

How to Mitigate CVE-2023-50387

Immediate Actions Required

Apply vendor-provided patches immediately
Enable rate limiting on DNS queries
Monitor DNS server logs for anomalies

Patch Information

Patches are available from various vendors, including Redhat and ISC, to mitigate the vulnerability in their respective DNS implementations.

Workarounds

Administrators can temporarily disable or limit DNSSEC validation features if patches cannot be applied immediately, focusing on balancing security and availability concerns.

bash

# Configuration example
sudo sh -c 'echo "rate_limit=250" >> /etc/named.conf'
systemctl restart named