CVE-2026-69847 Overview
CVE-2026-69847 is a heap-based buffer overflow [CWE-122] in the Windows Dynamic Host Configuration Protocol (DHCP) Server service. An authorized attacker on an adjacent network can trigger the overflow and execute arbitrary code in the context of the DHCP Server process. The flaw affects a wide range of Microsoft client and server operating systems, including Windows 10, Windows 11, and Windows Server versions from 2012 through 2025. Microsoft published the advisory on 2026-09-08 and updated the entry on 2026-09-10.
Critical Impact
Successful exploitation can result in remote code execution on Windows DHCP servers, compromising confidentiality, integrity, and availability of a service central to network operations.
Affected Products
- Microsoft Windows 10 (1607, 1809, 21H2, 22H2) across x86, x64, and ARM64 builds
- Microsoft Windows 11 (23H2, 24H2, 25H2, 26H1) across x64 and ARM64 builds
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-09-08 - CVE-2026-69847 published to the National Vulnerability Database
- 2026-09-10 - Last updated in NVD database
Technical Details for CVE-2026-69847
Vulnerability Analysis
The defect resides in the Windows DHCP Server service, which allocates buffers on the heap while parsing DHCP protocol structures. When the service processes a specially crafted request from an authenticated client on an adjacent network segment, the size of the destination buffer is smaller than the data written into it. The resulting heap corruption can be steered to overwrite adjacent allocations, function pointers, or metadata that the service later dereferences. Because the DHCP Server runs with elevated system privileges, code execution occurs in a highly trusted context and can be used to pivot deeper into the enterprise network.
Root Cause
The root cause is classified as a heap-based buffer overflow [CWE-122]. The DHCP Server code path does not correctly validate the length of attacker-controlled fields before copying them into a heap allocation. This lack of bounds enforcement allows adjacent heap memory to be corrupted during normal request processing.
Attack Vector
The attack vector is adjacent network, requiring the attacker to be present on the same broadcast domain, VLAN, or logically adjacent subnet as the DHCP Server. The attacker must also hold low-level authenticated privileges before sending the malicious DHCP traffic. No user interaction is required on the target, and the scope remains unchanged, meaning impact is contained to the vulnerable DHCP Server component but with high confidentiality, integrity, and availability effects.
No verified public exploit code or proof-of-concept has been observed. See the Microsoft Security Update Guide for authoritative technical details.
Detection Methods for CVE-2026-69847
Indicators of Compromise
- Unexpected crashes, restarts, or Watson error reports for the dhcpserver service or the svchost.exe instance hosting it.
- Anomalous child processes spawned by the DHCP Server service, particularly command shells or scripting engines.
- Malformed DHCP packets containing oversized option fields captured on the local subnet.
Detection Strategies
- Monitor Windows Event Logs on DHCP servers for service faults, access violations, and abnormal termination events tied to the DHCP Server role.
- Deploy network sensors that validate DHCP option length fields and flag requests exceeding expected sizes.
- Correlate authentication events on adjacent hosts with subsequent DHCP protocol anomalies to identify pre-exploitation reconnaissance.
Monitoring Recommendations
- Baseline normal DHCP request volumes and option distributions to make outliers visible in security analytics.
- Track process lineage for svchost.exe -k DHCPServer and alert on unexpected module loads or memory allocation patterns.
- Forward DHCP server logs and endpoint telemetry to a central SIEM to enable cross-host correlation.
How to Mitigate CVE-2026-69847
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft Security Update Guide to all affected DHCP servers as the primary remediation.
- Inventory every Windows host running the DHCP Server role, including domain controllers and branch office servers, and prioritize patching for internet-adjacent or multi-tenant segments.
- Restrict access to UDP ports 67 and 68 at the network boundary and within segmentation policies so only trusted clients can reach the DHCP service.
Patch Information
Microsoft has issued cumulative security updates addressing CVE-2026-69847 for all supported Windows client and server SKUs listed in the advisory. Refer to the Microsoft Security Update Guide for the specific KB article and build numbers that correspond to each affected version.
Workarounds
- Where patching is delayed, isolate DHCP servers on management VLANs and enforce 802.1X or MAC filtering to reduce the population of hosts that can authenticate on the adjacent network.
- Disable the DHCP Server role on hosts that no longer require it, and consolidate DHCP services onto a smaller, tightly monitored footprint.
- Enable DHCP snooping and rate limiting on network switches to constrain the ability of a compromised endpoint to reach the vulnerable service.
# Example: enumerate Windows hosts with the DHCP Server role and check patch status
Get-WindowsFeature -Name DHCP | Where-Object { $_.Installed -eq $true }
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
