CVE-2025-50334
📋 TL;DR
A vulnerability in Technitium DNS Server v13.5 allows remote attackers to trigger a denial of service condition by exploiting the rate-limiting component. This affects organizations running vulnerable versions of the DNS server, potentially disrupting DNS resolution services.
💻 Affected Systems
- Technitium DNS Server
📦 What is this software?
Dnsserver by Technitium
⚠️ Risk & Real-World Impact
Worst Case
Complete DNS service outage, preventing domain name resolution for all clients relying on the server, potentially disrupting business operations and internet connectivity.
Likely Case
Degraded DNS performance or intermittent service disruptions affecting users and applications dependent on the DNS server.
If Mitigated
Limited impact with proper network segmentation and rate-limiting controls in place upstream.
🎯 Exploit Status
The CWE-770 (Allocation of Resources Without Limits or Throttling) suggests this is relatively straightforward to exploit by overwhelming the rate-limiting mechanism.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v13.6 or later (based on changelog analysis)
Vendor Advisory: http://technitium.com
Restart Required: Yes
Instructions:
1. Backup current configuration. 2. Download latest version from technitium.com. 3. Stop DNS Server service. 4. Install/upgrade to v13.6+. 5. Restart DNS Server service. 6. Verify functionality.
🔧 Temporary Workarounds
Implement External Rate Limiting
allUse network firewall or load balancer to limit DNS query rates before reaching the vulnerable server.
Disable Rate Limiting (if possible)
allTemporarily disable the vulnerable rate-limiting component if the configuration allows it.
Edit DnsServer.config and set rate limiting to disabled mode
🧯 If You Can't Patch
- Isolate the DNS server behind a firewall with strict rate-limiting rules
- Implement monitoring and alerting for unusual DNS query patterns
🔍 How to Verify
Check if Vulnerable:
Check Technitium DNS Server version via web interface or configuration file. If version is exactly v13.5, system is vulnerable.Check Version:
On Windows: Check Services panel for Technitium DNS Server version. On Linux: Check /opt/technitium/version.txt or service status output.Verify Fix Applied:
Verify version is v13.6 or higher after upgrade. Test DNS functionality and monitor for service stability.📡 Detection & Monitoring
Log Indicators:
- Unusually high rate of DNS queries
- Rate limiting error messages
- Service restart events
Network Indicators:
- Spike in DNS traffic from single or multiple sources
- DNS response time degradation
SIEM Query:
source="dns_server" AND (message="rate limit*" OR message="denial*" OR message="overload*")🔗 References
- http://technitium.com
- https://github.com/FPokerFace/Security-Advisory/tree/main/CVE-2025-50334
- https://github.com/TechnitiumSoftware/DnsServer/blob/master/CHANGELOG.md
- https://github.com/TechnitiumSoftware/DnsServer/blob/v13.3/DnsServerCore/Dns/DnsServer.cs
- https://github.com/TechnitiumSoftware/DnsServer/commit/7229b217238213cc6275eea68a7e17d73df1603e
