CVE-2023-28456
📋 TL;DR
CVE-2023-28456 is a DNS amplification vulnerability in Technitium DNS Server that allows attackers to send small DNS queries that trigger large responses, enabling distributed denial-of-service (DDoS) attacks. The vulnerability amplifies traffic by approximately 3x compared to normal DNS responses, making it attractive for DDoS campaigns. Organizations running vulnerable Technitium DNS Server instances are affected.
💻 Affected Systems
- Technitium DNS Server
📦 What is this software?
Dnsserver by Technitium
⚠️ Risk & Real-World Impact
Worst Case
Attackers could use vulnerable servers as amplifiers in large-scale DDoS attacks, potentially taking down critical internet infrastructure or services by overwhelming them with amplified DNS traffic.
Likely Case
Vulnerable servers get abused as reflectors in DDoS attacks against third parties, consuming bandwidth and potentially causing service disruption for both the target and the vulnerable server's network.
If Mitigated
With proper network controls and patching, the risk is limited to potential bandwidth consumption if the server remains exposed but patched systems are not usable for amplification.
🎯 Exploit Status
The vulnerability requires no authentication and can be exploited with standard DNS query tools. Public proof-of-concept code demonstrates the amplification attack.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 11.0.3 and later
Vendor Advisory: https://technitium.com/dns/
Restart Required: Yes
Instructions:
1. Download Technitium DNS Server version 11.0.3 or later from the official website. 2. Stop the DNS server service. 3. Install the updated version. 4. Restart the DNS server service.
🔧 Temporary Workarounds
Rate Limiting Configuration
allConfigure DNS query rate limiting to reduce amplification potential
Edit Technitium DNS Server configuration to enable and tune rate limiting parameters
Network ACL Restrictions
allRestrict DNS queries to trusted sources only
Configure firewall rules to allow DNS queries only from authorized networks
🧯 If You Can't Patch
- Implement strict network access controls to limit DNS queries to trusted sources only
- Deploy upstream DDoS protection services or appliances to detect and mitigate amplification attacks
🔍 How to Verify
Check if Vulnerable:
Check Technitium DNS Server version via web interface or configuration file. Versions 11.0.2 and earlier are vulnerable.Check Version:
Check the web interface at http://localhost:5380 or examine the server configuration file for version informationVerify Fix Applied:
Verify the installed version is 11.0.3 or later and test with DNS amplification tools to confirm reduced response sizes.📡 Detection & Monitoring
Log Indicators:
- Unusually high DNS query volumes from single sources
- Large DNS response sizes in server logs
- Multiple identical query patterns from external IPs
Network Indicators:
- Spike in outbound DNS traffic from server
- DNS responses significantly larger than queries (3x amplification)
- UDP traffic patterns matching DDoS amplification
SIEM Query:
source="technitium-dns" AND (bytes_out > (bytes_in * 2.5)) OR (query_count > 1000 per source_ip per minute)