In 2022, Microsoft patched a critical vulnerability in its Windows DNS Server product, identified as CVE-2022-26814. This flaw allowed remote attackers to execute code on vulnerable servers, making it a significant threat to organizations relying on Windows DNS infrastructure. In this post, we'll break down how this bug works, what makes it dangerous, and what you can do to stay protected. This vulnerability is distinct from other CVEs released in the same patch cycle, including CVE-2022-24536 and others listed in this family of bugs.

What is CVE-2022-26814?

CVE-2022-26814 is a remote code execution (RCE) vulnerability in Microsoft Windows DNS Server. It received a high CVSS severity rating because, when exploited, it allows an unauthenticated attacker to send specially crafted DNS requests and gain control over the server—potentially leading to full domain compromise.

Official Microsoft Advisory

- Microsoft Security Guidance for CVE-2022-26814  
- June 2022 Patch Tuesday Release Notes

How Does the Vulnerability Work?

DNS servers resolve human-readable domain names into IP addresses. When a DNS Server receives a query from a client, it parses and processes the incoming request. CVE-2022-26814 existed due to improper validation of DNS request packets, specifically when handling certain types of requests. By exploiting this, a remote attacker could trigger a buffer overflow or memory corruption, resulting in arbitrary code execution in the context of the SYSTEM account.

Technical Details

While Microsoft didn’t release step-by-step exploit code, the general risk lies in how the DNS server processes malformed packets.

Simplified sequence

1. Attacker crafts a DNS query with a malformed header or payload targeting a specific DNS operation handled insecurely.

Vulnerable server receives and parses the malicious query.

3. Due to lack of robust validation, the server performs unsafe memory operations (such as buffer overflows), enabling code injection.

Proof-of-Concept Snippet

While a full working exploit is not available publicly and should not be shared due to ethical and legal reasons, below is a simplified Python snippet to demonstrate how such attacks usually start, by sending malformed DNS queries to the target.

> Disclaimer: This code is for educational purposes only. Do _not_ use it against systems you do not own.

import socket

target_dns = '192.168.1.10' # Change to your target DNS server IP
port = 53

# Craft a malformed UDP DNS packet (random bytes for demonstration)
malformed_query = b'\x00'*32 + b'A' * 512

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(malformed_query, (target_dns, port))
sock.close()

print("Malformed packet sent to", target_dns)

What does this do?
This doesn't exploit the real bug, but it represents an attacker's first step—sending non-standard queries to provoke unexpected server behavior.

Wormable: In some scenarios, an exploit could propagate itself, similar to WannaCry.

- Domain Compromise: DNS servers often run domain operations. Successful exploitation could give an attacker the keys to the entire Active Directory.

Potential attack surface and preconditions for exploitation.

Each CVE targets a separate issue, so patching one does not protect you from the others.

Mitigation and Patch

Microsoft’s Fix:  
Microsoft released patches as part of their June 2022 Patch Tuesday. All supported versions of Windows Server are affected.

Apply Patch:

- How to Update Windows Server

Limit external access to DNS servers whenever possible.

Workarounds:  
Disabling the DNS service where it’s not needed, or using firewalls to restrict incoming traffic to trusted IP sources.

Checking Your Patch Status

Run Windows Update or check your update history for patches released in June 2022. Specifically, look for updates listed in the Microsoft Advisory.

References & Further Reading

- Microsoft Security Update Guide – CVE-2022-26814
- MSRC Patch Tuesday Release Notes
- SANS ISC Diary: June 2022 Patch Analysis
- Talos Blog - DNS Server Vulnerabilities in 2022

Conclusion

CVE-2022-26814 underlines the importance of keeping network-facing infrastructure updated—it’s both a high-impact and actively targeted bug. While full exploit details are not public (due to the dangers involved), it shares key indicators with previous worms and high-severity vulnerabilities affecting core internet services.

Patch now, audit your DNS permissions, and monitor logs for suspicious traffic to help shield your environment from these attacks. If you’re responsible for a Windows DNS Server, this is one update you shouldn’t skip.

Timeline

Published on: 04/15/2022 19:15:00 UTC
Last modified on: 04/18/2022 20:15:00 UTC