Microsoft WSL: Heap-based buffer overflow allows local privilege escalation
Summary
A heap-based buffer overflow in the Windows Subsystem for Linux (WSL) allows an authorized local attacker to elevate privileges. The attacker needs an existing low-privileged account on the system and no user interaction is required. The impact is rated High for confidentiality, integrity and availability (CVSS 3.1 7.8).
Affected
- Windows 10 Version 21H2: 10.0.19044.0 to before 10.0.19044.7807
- Windows 10 Version 22H2: 10.0.19045.0 to before 10.0.19045.7807
- Windows 11 Version 23H2: 10.0.22631.0 to before 10.0.22631.7652
- Windows 11 Version 24H2: 10.0.26100.0 to before 10.0.26100.9711
- Windows 11 Version 25H2: 10.0.26200.0 to before 10.0.26200.9711
- Windows 11 Version 26H1: 10.0.28000.0 to before 10.0.28000.3231
- Windows 11 Version 26H2: 10.0.26300.0 to before 10.0.26300.9711
- Windows Server 2022: 10.0.20348.0 to before 10.0.20348.5761
- Windows Server 2025 (including Server Core): 10.0.26100.0 to before 10.0.26100.33650
Fixed in
- Windows 10 21H2: 10.0.19044.7807
- Windows 10 22H2: 10.0.19045.7807
- Windows 11 23H2: 10.0.22631.7652
- Windows 11 24H2: 10.0.26100.9711
- Windows 11 25H2: 10.0.26200.9711
- Windows 11 26H1: 10.0.28000.3231
- Windows 11 26H2: 10.0.26300.9711
- Windows Server 2022: 10.0.20348.5761
- Windows Server 2025: 10.0.26100.33650
- Patch vehicle: October 2026 cumulative updates. KB number for Windows 10 21H2 unknown; check the MSRC advisory.
Workaround
Unknown. No workaround is documented; patching is the stated remedy.
Exploitation
- Not known to be exploited in the wild; not on the CISA KEV list.
- EPSS score 0.00341 (about 0.3%).
- No public proof of concept found.
- CISA SSVC: exploitation none, not automatable, total technical impact.
Our recommendation
- Install the October 2026 cumulative update on all affected Windows 10, Windows 11 and Windows Server systems, prioritising systems with WSL, developer workstations, shared and terminal servers.
- Until patched, restrict local logon and shell access to trusted users on systems with WSL.
- Verify the affected build numbers on the MSRC advisory before rollout.
Information from Microsoft (Patch Tuesday October 2026)
- Severity (Microsoft)
- Important
- Impact
- Elevation of privilege – Windows Subsystem for Linux
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation unlikely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5127648, KB5126655, KB5126657, KB5126646, KB5126653, KB5127646
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-70027 msrc.microsoft.com
- Vulners: CVE-2026-70027 (CNA affected ranges) vulners.com
- Vulners: CVE-2026-70027 (CNA version data) vulners.com
- OpenCVE: CVE-2026-70027 (NVD/CVSS, mitigation, KEV) app.opencve.io
- Strix: CVE-2026-70027 (KEV status) www.strix.ai
- Vulners Rapid7: CVE-2026-70027 (EPSS) vulners.com
- Vulners PT Security: PT-2026-112171 (advisory notice) vulners.com
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 2 Nov 2026, 04:31.
Original description (NVD)
Heap-based buffer overflow in Windows Subsystem for Linux allows an authorized attacker to elevate privileges locally.
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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