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Windows Internet Information Services: Denial of service through integer underflow

CVE-2026-119936Medium 5.9

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Summary

Microsoft's Windows Internet Information Services (IIS) contains an integer underflow that allows a remote, unauthenticated attacker to cause a denial of service. Successful exploitation can crash or stall the web service. No confidentiality or integrity impact is listed, and the attack complexity is high. Systems without IIS installed are not affected.

Affected

  • Windows 10 Version 1607 and Windows Server 2016 (including Server Core): builds before 10.0.14393.9688
  • Windows 10 Version 1809 and Windows Server 2019 (including Server Core): builds before 10.0.17763.9487
  • Windows 10 Version 21H2 and 22H2: builds before 10.0.19044.7846 and 10.0.19045.7846
  • Windows 11 Version 23H2: builds before 10.0.22631.7711
  • Windows 11 Version 24H2 and 25H2: builds before 10.0.26100.9974 and 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 2022: builds before 10.0.20348.5870
  • Note: build numbers are taken from the CVE record and must be confirmed on the MSRC advisory.

Fixed in

  • Security update released on November 10, 2026 for each affected Windows build.
  • No separate IIS patch was found.
  • Windows 11 26H1 fix reportedly in KB5132059 (unverified).

Workaround

  • Unknown. No vendor-documented workaround was found.
  • Patch the affected systems.

Exploitation

  • Not known to be exploited in the wild.
  • No public proof of concept is known.
  • CVSS temporal vector uses exploit maturity 'Unproven'.
  • CISA SSVC: exploitation none, automatable no.
  • NVD analysis was pending at publication.

Our recommendation

  • Check whether IIS is installed on your Windows servers and clients.
  • Install the November 2026 security update, starting with internet-facing IIS servers.
  • Confirm the fixed build for each operating system on the MSRC advisory before rollout.
  • Monitor NVD and MSRC for changes in exploitation status.
  • Prioritise other critical IIS issues from the same release, such as CVE-2026-70024 and CVE-2026-119961.

Information from Microsoft (Patch Tuesday November 2026)

Severity (Microsoft)
Important
Impact
Denial of service – Windows Internet Information Services
Status on Patch Tuesday
Neither exploited nor publicly disclosed
Exploitability assessment
Exploitation less likely
Product family
Windows, Windows ESU (Extended Security Updates)
Updates (KB)
KB5131291, KB5131085, KB5131096, KB5131090, KB5131087, KB5132061

Entry in the Microsoft Security Update Guide

Public exploits

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

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, 15:14.

Original description (NVD)

Integer underflow (wrap or wraparound) in Windows Internet Information Services allows an unauthorized attacker to deny service over a network.

NVD references (1)

Sources

The tracker combines official, freely usable data sources – updated continuously:

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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