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For years, cybersecurity experts have warned about critical vulnerabilities in the Domain Name System (DNS), particularly in Microsoft’s implementation. The SIGRed (CVE-2020-1350) vulnerability, with a CVSS score of 10, exposed billions of users due to Microsoft’s DNS server flaws dating back to 2003. Despite warnings, including a 2008 private disclosure by the late Dan Kaminsky, Microsoft failed to address the issue promptly.
You Should Know: Critical DNS Security Practices
1. Detecting SIGRed Vulnerability
Check if your Windows Server is vulnerable using PowerShell:
Get-WindowsFeature -Name DNS | Where-Object Installed -eq $true
If DNS role is installed, apply Microsoft’s patch (KB4569509) immediately.
2. Mitigating DNS Attacks
- Enable DNS Cache Locking (Windows DNS Server):
Set-DnsServerCache -LockingPercent 100
- Disable Recursive Queries for external clients:
Set-DnsServerRecursion -Enable $false
- Enable DNSSEC Validation:
Set-DnsServerDnsSecZoneSetting -ZoneName "yourdomain.com" -Validation Enabled
3. Linux DNS Hardening (BIND9)
If using Linux DNS servers, secure BIND9:
sudo apt install bind9 bind9utils sudo nano /etc/bind/named.conf.options
Add:
options {
recursion no;
allow-query { trusted-IPs; };
dnssec-validation auto;
};
Restart BIND:
sudo systemctl restart bind9
4. Monitoring DNS Anomalies
Use Wireshark to detect malicious DNS traffic:
tshark -i eth0 -Y "dns.flags.response == 0" -T fields -e ip.src -e dns.qry.name
5. Microsoft’s Workaround (Before Patching)
Manually restrict TCP DNS payload size via Registry:
reg add "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DNS\Parameters" /v "TcpReceivePacketSize" /t REG_DWORD /d 0xFF00 /f
Restart DNS service:
Restart-Service DNS
What Undercode Say
Microsoft’s SIGRed flaw highlights systemic risks in DNS infrastructure. Organizations must:
– Patch immediately (CVE-2020-1350).
– Disable recursion for untrusted clients.
– Enforce DNSSEC to prevent spoofing.
– Monitor DNS logs for unusual queries.
– Migrate critical DNS zones to hardened Linux servers if possible.
Expected Output: A secure DNS setup with logging, patching, and restricted queries to mitigate SIGRed-like threats.
Relevant URLs:
References:
Reported By: Andy Jenkinson – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
