Microsoft Windows DNS Server: Use after free allows remote code execution
Summary
A use-after-free flaw in the Windows Domain Name Service (DNS Server) component allows an unauthenticated attacker to execute code remotely over the network. The CVSS base score is 8.1 (High), but the attack complexity is rated High and CISA SSVC reports no known exploitation and no automation. The issue affects the DNS Server role on supported Windows Server versions and on Windows 10 1607 as listed in the CPE data; the DNS Server role is normally not installed on Windows 10 clients.
Affected
- Windows 10 Version 1607 and Windows Server 2016 (incl. Server Core): builds below 10.0.14393.9612
- Windows 10 Version 1809 and Windows Server 2019 (incl. Server Core): builds below 10.0.17763.9376
- Windows Server 2012 and 2012 R2 (incl. Server Core): builds below 6.2.9200.26434 and 6.3.9600.23470
- Windows Server 2022: builds below 10.0.20348.5761
- Windows Server 2025 (incl. Server Core): builds below 10.0.26100.33650
Fixed in
- Windows 10 1607 / Server 2016: 10.0.14393.9612
- Windows 10 1809 / Server 2019: 10.0.17763.9376
- Windows Server 2012: 6.2.9200.26434
- Windows Server 2012 R2: 6.3.9600.23470
- Windows Server 2022: 10.0.20348.5761
- Windows Server 2025: 10.0.26100.33650
Install the latest Microsoft security update that contains the fix. KB numbers for all products were not verified; KB5126646 (Server 2025) and KB5126651 (1809 / Server 2019) are reported by a third party.
Workaround
- No vendor workaround known. Patching is the fix.
- Temporary measure, not from Microsoft: restrict inbound DNS traffic (TCP/UDP 53) to known trusted IP addresses until patched.
Exploitation
- CISA SSVC: Exploitation none, Automatable no, Technical Impact total.
- No evidence of exploitation in the wild found.
- No public proof of concept found.
- Not listed in CISA KEV.
Our recommendation
- Identify all Windows hosts with the DNS Server role and check their build numbers.
- Patch DNS servers promptly, starting with hosts reachable from untrusted networks and domain controllers running the DNS role.
- For Windows 2016 or 1607 hosts, check whether the system is still supported; unsupported systems may not receive this fix.
- Limit DNS listeners to required interfaces and restrict port 53 to required sources.
- Isolate DNS servers from general user networks and monitor them for unusual activity.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Role: DNS Server
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5126651, KB5126655, KB5126646, KB5126868, KB5126835, KB5126836
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- MSRC Security Update Guide: CVE-2026-70127 msrc.microsoft.com
- OpenCVE: CVE-2026-70127 app.opencve.io
- Vulners: CVE-2026-70127 vulners.com
- Strix: CVE-2026-70127 www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 1 Nov 2026, 19:33.
Original description (NVD)
Use after free in DNS Server allows an unauthorized attacker to execute code over a network.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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