CVE-2026-97817: DNS Server Buffer Overflow Vulnerability

CVE-2026-97817 Overview

CVE-2026-97817 is a heap-based buffer overflow vulnerability in Microsoft DNS Server. An authorized attacker can exploit the flaw over a network to disclose sensitive information from the DNS Server process memory. The issue is tracked under CWE-122: Heap-based Buffer Overflow.

The vulnerability requires low-level privileges and no user interaction. Successful exploitation does not alter data or availability, but it exposes confidential memory contents to the attacker. Microsoft published guidance in the Microsoft Security Update CVE-2026-97817 advisory.

Critical Impact
Authorized network attackers can read heap memory from the DNS Server process, potentially exposing cached records, credentials, or configuration data processed by dns.exe.

Affected Products

Microsoft DNS Server (see Microsoft Security Update CVE-2026-97817 for the full version matrix)
Windows Server deployments running the DNS Server role
Not Available

Discovery Timeline

2026-10-13 - CVE CVE-2026-97817 published to NVD
2026-10-13 - Last updated in NVD database

Technical Details for CVE-2026-97817

Vulnerability Analysis

The vulnerability resides in Microsoft DNS Server request handling logic. A heap-based buffer overflow occurs when the server processes a crafted DNS message that exceeds the bounds of an allocated heap buffer. Rather than enabling code execution, the condition leaks adjacent heap memory back to the attacker through server responses.

Because the DNS Server process routinely handles zone data, cached records, and operational metadata, the leaked memory can contain information useful for lateral movement or follow-on attacks. The flaw affects confidentiality only, not integrity or availability of the service.

Microsoft has not released public technical specifics beyond the advisory. Refer to the Microsoft Security Update CVE-2026-97817 for authoritative version and build information.

Root Cause

The root cause is improper validation of input length or structure before copying data into a heap-allocated buffer within the DNS Server service. When the attacker-controlled input exceeds expected bounds, the server reads or returns bytes beyond the intended buffer boundary. This disclosure pattern is classified under CWE-122.

Attack Vector

The attack vector is network-based with low attack complexity. The attacker must possess low-level privileges on the target environment, meaning the attacker is already authorized to send DNS queries to the server. No user interaction is required. The attacker sends crafted DNS protocol traffic to the server and observes the responses for leaked heap data.

No verified proof-of-concept code is available in public exploit databases at the time of publication. The current EPSS probability is approximately 0.95%.

See the Microsoft Security Update CVE-2026-97817 advisory for additional technical details.

Detection Methods for CVE-2026-97817

Indicators of Compromise

Unusual volume of malformed or oversized DNS queries directed at internal DNS servers from authenticated clients.
Anomalous outbound response sizes from dns.exe relative to query baselines, suggesting memory may be returned to the client.
Repeated DNS queries from a single source using uncommon record types or crafted name structures.

Detection Strategies

Enable DNS analytical and audit logging on Windows Server and forward events to a centralized SIEM for inspection.
Deploy network IDS signatures that flag non-conforming DNS packet structures and oversized record fields.
Baseline DNS query patterns per client and alert on statistical deviations in query type, size, or response length.

Monitoring Recommendations

Monitor the DNS Server process for crashes, exceptions, and memory anomalies logged in the Windows Event Log.
Correlate authenticated client activity with DNS query patterns to identify low-privilege accounts probing the service.
Alert on unexpected process behavior from dns.exe, including irregular memory allocation or unusual child process activity.

How to Mitigate CVE-2026-97817

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update CVE-2026-97817 advisory to all Windows Server systems running the DNS Server role.
Inventory all DNS Server instances across production, development, and disaster recovery environments and prioritize public-facing servers.
Review authentication requirements for DNS query submission and remove unnecessary low-privileged access.

Patch Information

Microsoft has released a security update for CVE-2026-97817. Administrators should consult the Microsoft Security Update CVE-2026-97817 page for build numbers, affected Windows Server versions, and KB article references. Install the update through Windows Update, WSUS, or your enterprise patch management platform.

Workarounds

Restrict network access to DNS Server to trusted internal subnets using host firewall rules or network ACLs.
Segment DNS infrastructure so that only authorized clients and forwarders can reach the service.
Increase monitoring of DNS traffic until patches are deployed to all affected servers.

bash

# Example: Restrict inbound DNS traffic to trusted subnet using Windows Firewall
New-NetFirewallRule -DisplayName "Restrict DNS to Trusted Subnet" `
  -Direction Inbound `
  -Protocol UDP `
  -LocalPort 53 `
  -RemoteAddress 10.0.0.0/8 `
  -Action Allow