Microsoft Windows: Heap-based buffer overflow in Microsoft XML
Summary
A heap-based buffer overflow in Microsoft XML, the XML parsing component used by Windows and applications that call it, allows remote code execution. An unauthenticated attacker with network access can trigger it with crafted XML, without user interaction. NVD rates it CVSS 9.8 (Critical). CISA SSVC data reports exploitation as none and automatable as yes, and no public exploit is listed.
Affected
- Windows 10 Version 1607 (10.0.14393.0 before 10.0.14393.9612)
- Windows Server 2016 (10.0.14393.0 before 10.0.14393.9612)
- Windows 10 Version 1809, 21H2, 22H2 and Windows 11 23H2, 24H2, 25H2, 26H1, 26H2 (see MSRC for exact builds)
- Windows Server 2012 and 2012 R2 (see MSRC for exact builds)
Fixed in
- Windows 10 Version 1607 and Windows Server 2016: build 10.0.14393.9612 or later
- Other listed products: the fixed builds are in the MSRC Security Update Guide
- Verify the build numbers on MSRC before rollout
Workaround
- Unknown. No vendor-documented workaround was found. Apply the security update.
Exploitation
- CISA SSVC: exploitation none, automatable yes, technical impact total
- Not listed in CISA KEV
- VulDB reports no exploit available
- VulDB reports exploit-market trading since 09/01/2026; this is a market estimate, not evidence of in-the-wild exploitation
Our recommendation
- Identify all Windows 10 1607 and Server 2016 hosts and their roles, with priority for internet-facing and DMZ systems.
- Check whether any service on these systems parses untrusted XML, such as web apps, APIs, ERP or document-processing tools.
- Install the October 2026 Microsoft security update and confirm the build number against the MSRC list.
- Check the Microsoft Lifecycle page for 1607 support status. If support has ended, plan an OS upgrade.
- Monitor CISA KEV and Microsoft advisories for changes.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Remote code execution – Microsoft XML
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation less likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5127648, KB5126651, KB5126655, KB5126657, KB5126646, KB5126653
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-83935 msrc.microsoft.com
- OpenCVE: CVE-2026-83935 app.opencve.io
- Vulners NVD record: CVE-2026-83935 vulners.com
- VulDB: CVE-2026-83935 vuldb.com
- Strix: CVE-2026-83935 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 30 Oct 2026, 18:31.
Original description (NVD)
Heap-based buffer overflow in Microsoft XML 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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