EUVD-2026-56650
GHSA-mwmg-vvvw-m6x8
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local vector and low-privilege requirement confirmed by description ('authorized attacker', 'locally'); full C/I/A reflects kernel-level privilege escalation impact.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Integer underflow (wrap or wraparound) in Windows HTTP.sys allows an authorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation via integer underflow in Windows HTTP.sys (the kernel-mode HTTP protocol stack) allows an authenticated local attacker to gain SYSTEM-level access on a broad range of Windows versions from Server 2012 through Server 2025 and Windows 10/11. The flaw is rooted in an integer wraparound condition (tagged by the reporter as a heap overflow mechanism) in the HTTP.sys kernel driver, enabling full compromise of confidentiality, integrity, and availability on the affected host. No public exploit has been identified at time of analysis, and Microsoft has released patches covering all affected version branches.
Technical ContextAI
HTTP.sys (http.sys) is a Windows kernel-mode driver implementing the HTTP/1.1 and HTTP/2 protocol stacks. It underpins IIS, WinRM, Windows Remote Desktop HTTP transports, and any application using the Windows HTTP Server API (HttpOpenServerSession/HttpReceiveHttpRequest). The root cause is classified as CWE-122 (Heap-based Buffer Overflow) in the NVD data, though the CVE description names the trigger as an integer underflow/wraparound (CWE-191). These are consistent: an integer underflow in a length or size calculation corrupts the computed allocation size, causing a downstream heap write to overflow its buffer - a classic interplay between the two CWE classes. Because HTTP.sys executes entirely in kernel space (Ring 0), a successful exploitation of its heap directly impacts kernel memory, giving the attacker leverage over kernel data structures. Affected builds span Windows NT 6.2 (Server 2012, build 6.2.9200.x) through Windows NT 10.0 (Windows 11 26H1, build 10.0.28000.x), indicating the vulnerable code path predates modern mitigations and persists across many kernel branches.
RemediationAI
The primary remediation is to apply Microsoft's monthly cumulative update to reach or exceed the fixed build version for each affected Windows release - exact target builds are listed in the affected products field above and in the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62741. Organizations using Windows Server Update Services (WSUS), Microsoft Update Catalog, or Intune should prioritize this patch for all internet-exposed or multi-user Windows Server deployments, particularly those running IIS, WinRM, or Remote Desktop gateway roles which rely on HTTP.sys. If patching cannot be applied immediately, a partial compensating control is to restrict local interactive and remote desktop access to only fully trusted administrator accounts, reducing the pool of principals who could trigger the vulnerable code path - note this does not eliminate risk from compromised service accounts that retain local logon rights. Windows Server 2012 and 2012 R2 are past mainstream support; organizations on these versions should treat the patch as urgent and simultaneously accelerate migration to a supported platform. No known workaround fully neutralizes the HTTP.sys attack surface short of the vendor patch.
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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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