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CVE-2020-1350, also known as SIGRed, was a critical remote code execution (RCE) vulnerability in Microsoft Windows DNS Server, scoring a perfect 10.0 on the CVSS scale. This flaw, present for 17 years, allowed attackers to compromise DNS servers remotely, leading to potential domain hijacking, data theft, and network-wide breaches.
You Should Know: How SIGRed Works & Mitigation Steps
Technical Analysis of SIGRed
The vulnerability resided in how Windows DNS Server handled specially crafted SIG records. Attackers could exploit this via a malicious DNS response, causing a heap-based buffer overflow, ultimately granting SYSTEM-level privileges.
Proof-of-Concept (PoC) Exploit Code
A simplified Python script to test DNS server vulnerability (for educational purposes only):
import socket
target_dns = "192.168.1.100" Replace with target DNS server
malicious_payload = (
b"\x00\x00\x01\x00\x00\x01\x00\x00\x00\x00\x00\x00"
b"\x07\x65\x78\x61\x6d\x70\x6c\x65\x03\x63\x6f\x6d\x00"
b"\x00\x01\x00\x01"
b"\x00\x00\x29\x10\x00\x00\x00\x80\x00\x00\x00"
)
sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(malicious_payload, (target_dns, 53))
response = sock.recv(4096)
print("Response:", response)
Mitigation Steps
1. Apply Microsoft’s Patch (July 2020):
wusa.exe /quiet /norestart WindowsServer-KB4569509-x64.msu
2. Disable DNS Server Recursion (if not needed):
Set-DnsServerRecursion -Enable $false
3. Block SIG Requests via Firewall:
iptables -A INPUT -p udp --dport 53 -m string --hex-string "|00 00 29|" --algo bm -j DROP
4. Enable DNSSEC Validation:
Set-DnsServerGlobalNameProtection -Enable $true
Post-Exploitation Detection
Check for exploitation attempts in Windows Event Logs:
Get-WinEvent -FilterHashtable @{LogName='DNS Server'; ID=150, 708}
What Undercode Say
SIGRed was a stark reminder of how legacy code and poor DNS hygiene can lead to catastrophic breaches. Despite patches, many organizations still neglect DNS security, leaving them exposed to similar attacks.
Expected Output:
- A patched DNS server should reject malformed SIG requests.
- Unpatched systems may crash or allow RCE.
- Monitoring logs for Event ID 150 (DNS Server Error) is crucial.
Prediction
Future DNS-based attacks will likely exploit zero-day vulnerabilities in DNSSEC or DoH (DNS-over-HTTPS), requiring stricter protocol-level hardening.
Relevant URLs:
References:
Reported By: Andy Jenkinson – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
