Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Network-reachable, unauthenticated, low-complexity resource-exhaustion DoS with no confidentiality or integrity impact, so AV:N/AC:L/PR:N/UI:N and A:H only.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Allocation of resources without limits or throttling in Windows HTTP.sys allows an unauthorized attacker to deny service over a network.
AnalysisAI
Denial of service in Microsoft Windows HTTP.sys allows remote unauthenticated attackers to exhaust system resources and make affected hosts unresponsive over the network. The flaw stems from missing resource limits/throttling (CWE-770) in the kernel-mode HTTP protocol stack, affecting a broad range of Windows client and server releases from Windows 10 1607 through Windows 11 26H1 and Windows Server 2016 through 2025. No public exploit identified at time of analysis, and the issue is not listed in CISA KEV; a vendor patch is available via MSRC.
Technical ContextAI
HTTP.sys is the kernel-mode HTTP protocol stack (http.sys driver) that underpins IIS and any application using the Windows HTTP Server API, handling connection management, request parsing, and response queuing before requests reach user-mode services. The root cause is CWE-770 (Allocation of Resources Without Limits or Throttling): the driver fails to bound some resource - such as memory, connection state, or queued request objects - allowing an attacker to force unbounded consumption. Because HTTP.sys runs in the kernel and fronts web-facing services on Windows Server (IIS, WinRM, WSUS, and other HTTP.sys-based listeners) and Windows clients, resource exhaustion here degrades or halts service availability system-wide rather than for a single application.
RemediationAI
Patch available per vendor advisory: apply the Microsoft security update for your specific Windows build as listed in the MSRC guidance at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-49787 (exact fixed KB/build numbers are provided there per OS version). Prioritize internet-facing IIS and HTTP.sys-based servers (Windows Server 2016/2019/2022/2025). Where immediate patching is not possible, reduce exposure by restricting network access to HTTP/HTTPS listeners via host or perimeter firewall rules so only trusted clients can reach the affected endpoints, and place vulnerable servers behind a reverse proxy or load balancer that enforces connection rate limiting and request throttling - noting the trade-off that these controls reduce but do not eliminate the resource-exhaustion vector and add infrastructure/latency overhead. Disabling non-essential HTTP.sys listeners (e.g. unused WinRM or legacy web endpoints) further shrinks attack surface.
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External POC / Exploit Code
Leaving vuln.today
EUVD-2026-43802
GHSA-5h64-g45f-7wgq