In April 2022, Microsoft disclosed several remote code execution (RCE) vulnerabilities in Windows DNS Server. Amongst them, CVE-2022-26811 stands out with its unique impact and exploitation vector, setting it apart from its siblings like CVE-2022-24536 or CVE-2022-26819. This long-read will guide you through what CVE-2022-26811 is all about, how attackers can exploit it, example code, and how you can protect your systems. The goal is to help Windows administrators and curious engineers grasp this threat in plain, clear language.

What is CVE-2022-26811?

CVE-2022-26811 is a critical security bug (CVSS Score: 8.8) affecting Microsoft Windows DNS Server. According to the official Microsoft advisory, this vulnerability allows an authenticated attacker to execute arbitrary code on the target DNS server. This happens due to improper validation of queries received by the DNS service.

In short, if an attacker sends a specially crafted DNS request to a vulnerable server, they might be able to take control of that server—a worst-case scenario, especially in networks where DNS servers run with high privileges.

How is CVE-2022-26811 Different?

There were a lot of DNS vulnerabilities fixed by Microsoft in early 2022 (such as CVE-2022-24536, CVE-2022-26812, through CVE-2022-26829). But CVE-2022-26811 is unique primarily in its triggering conditions and the code path it affects within the DNS server. If you’re searching for info, make sure you’re not mixing this up with the other CVEs!

Here’s a stepwise breakdown

1. Malicious Client Contact: The attacker, from anywhere they can reach the DNS server, crafts a malicious DNS query.

Vulnerable Parsing: The DNS Server improperly validates or parses parts of the incoming query.

3. Remote Code Execution: This flaw allows the attacker to potentially run code in the context of the DNS Server service, resulting in full takeover.

Why is this scary?  
Windows DNS Servers generally run under the SYSTEM account, which is the highest privilege level on Windows systems. So, if compromised, an attacker essentially controls the server.

A Closer Look: Example Exploit Snippet

To exploit this type of vulnerability, attackers often use low-level tools to craft their DNS packets. Tools like Scapy in Python or network utilities like dig or dnspython can be used. Here is a conceptual snippet (note: this is for educational purposes only!).

# This is a *conceptual* example -- not a weaponized exploit!
from scapy.all import *

# Malformed DNS packet generation
dns_query = IP(dst="192.168.1.10")/UDP(dport=53)/DNS(
    id=1337, 
    qr=, 
    qdcount=1, 
    ancount=, 
    nscount=, 
    arcount=, 
    qd=DNSQR(qname="malicious.example.com", qtype="A")
)

# Send the packet
send(dns_query)

Attackers would modify the packet further to trigger the vulnerable code path described in CVE-2022-26811. For actual exploitation, they'd need to deeply understand the bug specifics (often via reverse engineering the patch, analyzing DNS handling functions, and crafting binary-level input).

Original References

- Microsoft Security Advisory – CVE-2022-26811  
- NIST NVD – CVE-2022-26811
- Patch Analysis and DNS Exploitation Overview by SANS ISC
- Scapy - A powerful Python-based network packet manipulator & generator

Exploit Details in Simple Terms

*Attackers do not need to be in the same organization or domain as the victim DNS server.*

Sending a specially crafted DNS query that takes advantage of the improper input validation.

- Causing the DNS server process to execute attacker-controlled code, often installing malware, creating persistence, or pivoting further in the network.

Proof-of-concepts for this bug are not widely published, which is common for high-severity Windows server issues. However, understanding packet construction—like the simple Scapy example—shows how accessible the attack surface can be.

How to Detect if You're Vulnerable

1. Check Windows Version: The vulnerability impacts Windows Server 2012, 2016, 2019, and 2022 where DNS server role is installed.
2. Check Patch Status: Ensure your servers have the April 2022 cumulative update (or later) applied.

You can use PowerShell to check your patch status

Get-HotFix | Where-Object {$_.Description -like "*Security Update*" -and $_.InstalledOn -gt (Get-Date "2022-04-12")}

Microsoft has released patches in April 2022's Patch Tuesday. All you need to do is

- Update Windows Servers with the official Microsoft security updates (Visit Microsoft’s Update Guide for direct links)

Restart DNS Server Service after patching.

- Block Untrusted Access: If possible, restrict who can send packets to your DNS server. Use firewall rules to allow only trusted clients.

Real-World Impact

Left unpatched, exploitation of CVE-2022-26811 could have catastrophic impact. Attackers who compromise a DNS server could:

Use the server as a launchpad for further attacks into your network

This is why security teams should *always* prioritize DNS server updates.

Final Thoughts

CVE-2022-26811 isn't just another Windows bug—it's a reminder that core network services like DNS remain hot targets. Unlike bugs that require social engineering or user action, this flaw can be exploited *directly* over the network, so don’t delay your patching routine.

Stay tuned to

- Microsoft Security Update Guide
- CVE details for all DNS bugs like CVE-2022-26812, CVE-2022-26814, etc.

Be proactive—update, restrict, monitor. Don’t be the next headline.

Timeline

Published on: 04/15/2022 19:15:00 UTC
Last modified on: 04/18/2022 20:33:00 UTC