CVE-2026-70307: Windows Ancillary Function Driver for WinSock Elevation of Privilege Vulnerability

CVE-2026-70307 is an elevation of privilege vulnerability in Windows Ancillary Function Driver for WinSock, rated Important by Microsoft, with a CVSS 3.1 base score of 7 (High). An attacker can exploit it by an attacker with local access, with low privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as more likely. The EPSS model estimates a 0.26% probability of exploitation activity in the next 30 days, higher than 18% of all scored vulnerabilities. Microsoft released the fix on 11 August 2026 in the August 2026 Patch Tuesday, delivered through 13 security updates (KB5120238, KB5120242, KB5120229, KB5120249 and more). It affects 30 products in 2 product families (Windows, ESU).

Key facts

CVE ID: CVE-2026-70307
Severity: High CVSS 7
Microsoft severity: Important
Impact: Elevation of Privilege
Exploited in the wild: No
Publicly disclosed: No
Exploitation likelihood: More Likely
Weakness: CWE-416
EPSS: 0.26% (percentile 18%)
CISA KEV: Not listed
Released: 11 August 2026
Last updated: 11 August 2026
Patch Tuesday: August 2026 Patch Tuesday
Product families: Windows, ESU

CVSS score and vector

Microsoft scores CVE-2026-70307 at 7 (temporal 6.1) using CVSS 3.1. Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

Metric	Value
Attack vector	Local
Attack complexity	High
Privileges required	Low
User interaction	None
Scope	Unchanged
Confidentiality impact	High
Integrity impact	High
Availability impact	High
Exploit code maturity	Unproven
Remediation level	Official fix
Report confidence	Confirmed

Description

Use after free in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

Frequently asked questions (Microsoft)

What privileges could be gained by an attacker who successfully exploited this vulnerability?

An attacker who successfully exploited this vulnerability could gain SYSTEM privileges.

According to the CVSS metric, the attack complexity is high (AC:H). What does that mean for this vulnerability?

Successful exploitation of this vulnerability requires an attacker to win a race condition.

Affected products (30)

Windows

Product	Security update	Type	Fixed build	Restart
Windows 10 Version 1809 for 32-bit Systems	KB5120238	Security Update	10.0.17763.9121	Yes
Windows 10 Version 1809 for x64-based Systems	KB5120238	Security Update	10.0.17763.9121	Yes
Windows Server 2019	KB5120238	Security Update	10.0.17763.9121	Yes
Windows Server 2019 (Server Core installation)	KB5120238	Security Update	10.0.17763.9121	Yes
Windows Server 2022	KB5120242 KB5120229	Security Update Security Hotpatch Update	10.0.20348.5499 10.0.20348.5440	Yes Yes
Windows Server 2022 (Server Core installation)	KB5120242 KB5120229	Security Update Security Hotpatch Update	10.0.20348.5499 10.0.20348.5440	Yes Yes
Windows 10 Version 21H2 for 32-bit Systems	KB5120249	Security Update	10.0.19044.7663	Yes
Windows 10 Version 21H2 for ARM64-based Systems	KB5120249	Security Update	10.0.19044.7663	Yes
Windows 10 Version 21H2 for x64-based Systems	KB5120249	Security Update	10.0.19044.7663	Yes
Windows Server 2025 (Server Core installation)	KB5120233 KB5120228	Security Update Security Hotpatch Update	10.0.26100.33296 10.0.26100.33222	Yes Yes
Windows 11 Version 25H2 for ARM64-based Systems	KB5121003 KB5120994	Security Update Security Hotpatch Update	10.0.26200.9168 10.0.26200.9106	Yes Yes
Windows 11 Version 25H2 for x64-based Systems	KB5121003 KB5120994	Security Update Security Hotpatch Update	10.0.26200.9168 10.0.26200.9106	Yes Yes
Windows 11 Version 23H2 for ARM64-based Systems	KB5120240	Security Update	10.0.22631.7517	Yes
Windows 11 Version 23H2 for x64-based Systems	KB5120240	Security Update	10.0.22631.7517	Yes
Windows 11 Version 24H2 for ARM64-based Systems
Windows 11 Version 24H2 for x64-based Systems
Windows Server 2025	KB5120233 KB5120228	Security Update Security Hotpatch Update	10.0.26100.33296 10.0.26100.33222	Yes Yes
Windows 11 version 26H1 for x64-based Systems	KB5121000	Security Update	10.0.28000.2704	Yes
Windows 11 Version 26H1 for ARM64-based Systems	KB5121000	Security Update	10.0.28000.2704	Yes
Windows 10 Version 1607 for 32-bit Systems	KB5120418	Security Update	10.0.14393.9418	Yes
Windows 10 Version 1607 for x64-based Systems	KB5120418	Security Update	10.0.14393.9418	Yes
Windows Server 2016	KB5120418	Security Update	10.0.14393.9418	Yes
Windows Server 2016 (Server Core installation)	KB5120418	Security Update	10.0.14393.9418	Yes

ESU

Product	Security update	Type	Fixed build	Restart
Windows 10 Version 22H2 for x64-based Systems
Windows 10 Version 22H2 for ARM64-based Systems
Windows 10 Version 22H2 for 32-bit Systems
Windows Server 2012	KB5120386	Monthly Rollup	6.2.9200.26280	Yes
Windows Server 2012 (Server Core installation)	KB5120386	Monthly Rollup	6.2.9200.26280	Yes
Windows Server 2012 R2	KB5120385	Monthly Rollup	6.3.9600.23338	Yes
Windows Server 2012 R2 (Server Core installation)	KB5120385	Monthly Rollup	6.3.9600.23338	Yes

Security updates (13)

KB5120238 (Security Update)
KB5120242 (Security Update)
KB5120229 (Security Hotpatch Update)
KB5120249 (Security Update)
KB5120233 (Security Update)
KB5120228 (Security Hotpatch Update)
KB5121003 (Security Update)
KB5120994 (Security Hotpatch Update)
KB5120240 (Security Update)
KB5121000 (Security Update)
KB5120418 (Security Update)
KB5120386 (Monthly Rollup)
KB5120385 (Monthly Rollup)

NIST NVD data

NVD status: Analyzed
NVD CVSS: 7 (HIGH)
NVD weakness: CWE-416
Published to NVD: 11 August 2026
NVD last modified: 14 August 2026

Affected configurations (CPE)

Product	Vulnerable versions
windows 10 1607 (x64)	before 10.0.14393.9418
windows 10 1607 (x86)	before 10.0.14393.9418
windows 10 1809 (x64)	before 10.0.17763.9115
windows 10 1809 (x86)	before 10.0.17763.9115
windows 10 21h2 (arm64)	before 10.0.19044.7663
windows 10 21h2 (x64)	before 10.0.19044.7663
windows 10 21h2 (x86)	before 10.0.19044.7663
windows 10 22h2 (arm64)	before 10.0.19045.7663
windows 10 22h2 (x64)	before 10.0.19045.7663
windows 10 22h2 (x86)	before 10.0.19045.7663
windows 11 23h2 (arm64)	before 10.0.22631.7517
windows 11 23h2 (x64)	before 10.0.22631.7517
windows 11 24h2 (arm64)	before 10.0.26100.9106
windows 11 24h2 (x64)	before 10.0.26100.9106
windows 11 25h2 (arm64)	before 10.0.26200.9106
windows 11 25h2 (x64)	before 10.0.26200.9106
windows 11 26h1 (arm64)	before 10.0.28000.2704
windows 11 26h1 (x64)	before 10.0.28000.2704
windows server 2012	all listed versions
windows server 2012 r2	all listed versions
windows server 2016	before 10.0.14393.9418
windows server 2019	before 10.0.17763.9115
windows server 2022	before 10.0.20348.5440
windows server 2025	before 10.0.26100.33222

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-70307 (Vendor Advisory, Patch)

Acknowledgments

Owen McCullough with MSRC V&M

Revision history

Version	Date	Description
1.0	11 August 2026	Information published.