CVE-2026-65799 Overview
CVE-2026-65799 is an integer overflow or wraparound vulnerability in Windows DNS. The flaw allows an authorized attacker with high privileges to elevate privileges locally on affected systems. Microsoft published the advisory on 2026-08-11, and the vulnerability is tracked under CWE-122 (heap-based buffer overflow) resulting from arithmetic wraparound during DNS data handling. Successful exploitation compromises confidentiality, integrity, and availability on the affected host. The current EPSS probability is 0.256%, indicating low observed likelihood of exploitation in the near term.
Critical Impact
An authenticated local attacker can trigger an integer overflow in the Windows DNS component to escalate privileges, gaining full control of confidentiality, integrity, and availability on the affected system.
Affected Products
- Windows DNS (Microsoft Windows)
- Specific product versions listed in the Microsoft Security Update Guide
Discovery Timeline
- 2026-08-11 - CVE-2026-65799 published to NVD
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2026-65799
Vulnerability Analysis
The vulnerability resides in the Windows DNS component and stems from an integer overflow or wraparound condition. When arithmetic on size or length values wraps past the maximum representable value, the resulting undersized allocation or bounds calculation leads to a heap-based buffer overflow classified as [CWE-122]. An authorized attacker who can supply crafted DNS-related input to the affected local process can trigger this condition to corrupt adjacent heap memory. Because the affected code executes with elevated privileges, the resulting memory corruption can be leveraged to run code in a higher-privileged context. The outcome is full local privilege escalation on the affected host.
Root Cause
The root cause is unchecked or improperly validated arithmetic on integer values used for buffer sizing or offset calculations within the Windows DNS component. When these values wrap, subsequent memory operations write outside the intended allocation and corrupt heap metadata or adjacent objects.
Attack Vector
Exploitation requires local access and existing high-privilege credentials on the target host. No user interaction is required. The attacker interacts with the vulnerable DNS component to submit malformed input that drives the integer wraparound and subsequent heap overflow. Refer to the Microsoft Security Update Guide for component-level technical detail.
Detection Methods for CVE-2026-65799
Indicators of Compromise
- Unexpected crashes, access violations, or memory corruption events involving the Windows DNS service or client process.
- Creation of new local accounts or privilege changes following anomalous DNS-related process activity.
- Child processes spawned from the DNS service context that execute unusual binaries or scripts.
Detection Strategies
- Monitor Windows Event Logs for DNS service crashes, Application Error entries (Event ID 1000), and Windows Error Reporting events tied to dns.exe or DNS-related modules.
- Enable and review Sysmon process creation and image load events for suspicious activity originating from DNS-related processes.
- Correlate authentication events with anomalous local process behavior to detect post-exploitation privilege escalation.
Monitoring Recommendations
- Baseline normal DNS service memory usage and process behavior, and alert on deviations.
- Track patch compliance state across Windows hosts running the DNS role or DNS client components.
- Aggregate endpoint telemetry into a central data lake for retrospective hunting once patch and IoC details are published.
How to Mitigate CVE-2026-65799
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft Security Update Guide as soon as it is available in your patch cycle.
- Audit and restrict membership of local administrator and DNS-management groups to reduce the pool of accounts able to satisfy the high-privilege precondition.
- Prioritize patching on domain controllers and servers hosting the DNS Server role.
Patch Information
Microsoft addresses CVE-2026-65799 through its regular security update channel. Consult the Microsoft Security Update Guide for the exact KB identifiers, affected build numbers, and update packages for each supported Windows release.
Workarounds
- No official vendor workaround is listed. Apply the security update as the primary remediation.
- Where patching must be delayed, enforce least privilege and restrict interactive and remote logon rights on hosts running the DNS role.
- Monitor endpoints for the detection indicators listed above and investigate anomalies promptly.
# Verify installed Windows updates on a host (PowerShell)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
# Check DNS Server service status
Get-Service -Name DNS
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
