Windows Schannel: Remote code execution via timing discrepancy
Summary
Microsoft's Windows Schannel TLS component contains an observable timing discrepancy (CWE-208). According to the description, an unauthenticated attacker on the network could execute code on affected Windows systems. The attack complexity is high (AC:H), and the CVSS 3.1 base score is 8.1. NVD analysis was still pending at publication.
Affected
- Windows 10 Version 1607 (builds before 10.0.14393.9688)
- Windows 10 Version 1809 (builds before 10.0.17763.9487)
- Windows 10 Version 21H2 (builds before 10.0.19044.7846)
- Windows 10 Version 22H2 (builds before 10.0.19045.7846)
- Windows 11 Version 23H2 (builds before 10.0.22631.7711)
- Windows 11 Version 24H2 (builds before 10.0.26100.9974)
- Windows 11 Version 25H2 (builds before 10.0.26200.9974)
- Windows 11 Version 26H1 (builds before 10.0.28000.3501)
- Windows 11 Version 26H2 (builds before 10.0.26300.9974)
- Windows Server 2016, including Server Core (builds before 10.0.14393.9688)
- Windows Server 2019, including Server Core (builds before 10.0.17763.9487)
- Windows Server 2022 (builds before 10.0.20348.5870)
Source: official CVE record; not yet confirmed on the MSRC page.
Fixed in
- November 2026 Windows security updates (cumulative updates and hotpatches). Fixed builds: 10.0.14393.9688, 10.0.17763.9487, 10.0.19044.7846, 10.0.19045.7846, 10.0.22631.7711, 10.0.26100.9974, 10.0.26200.9974, 10.0.28000.3501, 10.0.26300.9974, 10.0.20348.5870.
- The applicable KB number per build is unknown; check the MSRC page.
Workaround
- Unknown. Microsoft's guidance is to install the November 2026 Windows updates.
- No separate Microsoft workaround was found.
Exploitation
- CISA SSVC assessment: exploitation none, not automatable, total technical impact.
- Not publicly disclosed and not known to be exploited in the wild, according to the sources found.
- Absence of evidence is not proof that no exploit exists.
Our recommendation
- Install the November 2026 Windows security update or hotpatch on all affected systems, prioritising servers and hosts exposed to untrusted networks.
- Verify the build number after patching against the fixed builds listed above.
- Check whether any system runs a Windows edition that is past end of servicing.
- Monitor the MSRC page and CISA KEV for changes in exploitation status.
Information from Microsoft (Patch Tuesday November 2026)
- Severity (Microsoft)
- Critical
- Impact
- Remote code execution – Windows Schannel
- Status on Patch Tuesday
- Neither exploited nor publicly disclosed
- Exploitability assessment
- Exploitation more likely
- Product family
- Windows, Windows ESU (Extended Security Updates)
- Updates (KB)
- KB5131291, KB5131085, KB5131096, KB5131090, KB5131087, KB5132061
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Response Center: CVE-2026-119952 msrc.microsoft.com
- Microsoft Windows message center (release health) learn.microsoft.com
- Rapid7: Patch Tuesday November 2026 www.rapid7.com
- Qualys: Microsoft Patch Tuesday November 2026 review blog.qualys.com
- Rescana: Microsoft Patch Tuesday November 2026 www.rescana.com
- Tenable: Microsoft November 2026 Patch Tuesday www.tenable.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 11 Nov 2026, 01:41.
Original description (NVD)
Observable timing discrepancy in Windows Schannel 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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