CVE-2023-21535: Windows Secure Socket Tunneling Protocol (SSTP) Remote Code Execution Vulnerability

Severity: high (CVSS 8.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2023-01-10 · updated 2026-06-17
Weakness: CWE-591

Description

Windows Secure Socket Tunneling Protocol (SSTP) Remote Code Execution Vulnerability

Affected products

Microsoft Windows 10 1607: all versions
Microsoft Windows 10: all versions
Microsoft Windows 10 20H2: all versions
Microsoft Windows 10: all versions
Microsoft Windows 10: all versions
Microsoft Windows 11 21H2: all versions
Microsoft Windows 11: all versions
Microsoft Windows 8.1: all versions
Microsoft Windows RT 8.1: all versions
Microsoft Windows Server 2008: r2-sp1
Microsoft Windows Server 2012: r2
Microsoft Windows Server 2016: all versions
Microsoft Windows Server 2019: all versions
Microsoft Windows Server 2022: all versions
Microsoft Windows 10 Version 1507: from 10.0.10240.0 before 10.0.10240.19685 — fixed in 10.0.10240.19685
Microsoft Windows 10 1607: from 10.0.14393.0 before 10.0.14393.5648 — fixed in 10.0.14393.5648
Microsoft Windows 10: from 10.0.17763.0 before 10.0.17763.3887 — fixed in 10.0.17763.3887
Microsoft Windows 10 20H2: from 10.0.0 before 10.0.19042.2486 — fixed in 10.0.19042.2486
Microsoft Windows 10: from 10.0.19043.0 before 10.0.19044.2486 — fixed in 10.0.19044.2486
Microsoft Windows 10: from 10.0.19045.0 before 10.0.19045.2486 — fixed in 10.0.19045.2486
Microsoft Windows 11 21H2: from 10.0.0 before 10.0.22000.1455 — fixed in 10.0.22000.1455
Microsoft Windows 11: from 10.0.22621.0 before 10.0.22621.1105 — fixed in 10.0.22621.1105
Microsoft Windows 8.1: from 6.3.0 before 6.3.9600.20778 — fixed in 6.3.9600.20778
Microsoft Windows Server 2008 Service Pack 2: from 6.0.6003.0 before 6.0.6003.21872 — fixed in 6.0.6003.21872
Microsoft Windows Server 2012: from 6.2.9200.0 before 6.2.9200.24075 — fixed in 6.2.9200.24075
Microsoft Windows Server 2012 R2: from 6.3.9600.0 before 6.3.9600.20778 — fixed in 6.3.9600.20778
Microsoft Windows Server 2016: from 10.0.14393.0 before 10.0.14393.5648 — fixed in 10.0.14393.5648
Microsoft Windows Server 2019: from 10.0.17763.0 before 10.0.17763.3887 — fixed in 10.0.17763.3887
Microsoft Windows Server 2022: from 10.0.20348.0 before 10.0.20348.1487 — fixed in 10.0.20348.1487

How to fix

Upgrade to a fixed version: Microsoft Windows 10 Version 1507 10.0.10240.19685; Microsoft Windows 10 1607 10.0.14393.5648; Microsoft Windows 10 10.0.17763.3887; Microsoft Windows 10 20H2 10.0.19042.2486; Microsoft Windows 10 10.0.19044.2486; Microsoft Windows 10 10.0.19045.2486; Microsoft Windows 11 21H2 10.0.22000.1455; Microsoft Windows 11 10.0.22621.1105; Microsoft Windows 8.1 6.3.9600.20778; Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21872; Microsoft Windows Server 2012 6.2.9200.24075; Microsoft Windows Server 2012 R2 6.3.9600.20778. Check the vendor advisory for mitigations.

References

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