EUVD-2026-56366
GHSA-jhr5-7989-3r59
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local kernel driver exploit via authenticated low-privilege account; no UI needed; full SYSTEM-level C/I/A impact; scope unchanged to single host.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Heap-based buffer overflow in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation via heap-based buffer overflow in Windows HTTP.sys (a kernel-mode HTTP listener driver) allows a locally authenticated low-privilege attacker to gain SYSTEM-level access across a broad range of Windows client and server releases. The CVSS vector (AV:L/AC:L/PR:L/UI:N) confirms exploitation requires only local authenticated access with no user interaction and low attack complexity, making this a practical post-compromise escalation primitive. No public exploit or CISA KEV listing has been identified at time of analysis, and Microsoft has released patches for all affected product lines.
Technical ContextAI
HTTP.sys (sys/http.sys) is a Windows kernel-mode driver that implements the core HTTP protocol stack, intercepting and processing HTTP requests at ring-0 before they reach user-space services such as IIS. CWE-122 (Heap-based Buffer Overflow) indicates the defect involves writing beyond the bounds of a heap-allocated buffer within this kernel driver. Because HTTP.sys runs in kernel context, a successful overflow can corrupt adjacent kernel memory structures - such as pool headers, function pointers, or security tokens - enabling an attacker to hijack execution flow or manipulate privilege tokens to achieve SYSTEM-level code execution. Affected CPE targets span Windows NT kernel builds from 6.2 (Windows Server 2012) through 10.0.28000 (Windows 11 26H1), confirming the flaw spans over a decade of Windows releases and is present in both client and server editions.
RemediationAI
Apply the Microsoft-released security update immediately for each affected platform. The patched builds are: Windows 10 1607 and Server 2016 - build 10.0.14393.9418 or later; Windows 10 1809, Server 2019 - 10.0.17763.9115 or later; Windows 10 21H2 - 10.0.19044.7663 or later; Windows 10 22H2 - 10.0.19045.7663 or later; Windows 11 23H2 - 10.0.22631.7517 or later; Windows 11 24H2 and Server 2025 - 10.0.26100.9168 (client) / 10.0.26100.33296 (server) or later; Windows 11 25H2 - 10.0.26200.9168 or later; Windows 11 26H1 - 10.0.28000.2704 or later; Windows Server 2012 - 6.2.9200.26279 or later; Windows Server 2012 R2 - 6.3.9600.23337 or later; Windows Server 2022 - 10.0.20348.5499 or later. Updates are available via Windows Update, WSUS, and the Microsoft Update Catalog. As a compensating control where patching is not immediately possible, restrict local interactive and remote desktop login to only necessary administrative accounts, reducing the pool of identities an adversary could leverage. Note that HTTP.sys cannot be simply disabled without breaking IIS and other HTTP-dependent services, so disabling the driver is not a viable standalone workaround. Consult the advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62735 for the full patch manifest.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
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