EUVD-2026-56666
GHSA-54rj-g9cv-7m8j
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Network-reachable SMB with low-privilege auth required; no interaction needed; full CIA impact upon successful kernel-mode code execution.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Heap-based buffer overflow in Windows SMB Server allows an authorized attacker to execute code over a network.
AnalysisAI
Remote code execution in Windows SMB Server is achievable by a network-authenticated attacker exploiting a heap-based buffer overflow (CWE-122). The CVSS vector (AV:N/AC:L/PR:L/UI:N) confirms that low-privileged, network-accessible credentials are sufficient - no user interaction or elevated rights are required. The vulnerability affects a broad range of Windows client and server releases from Windows Server 2012 through Windows 11 26H2 and Windows Server 2025, with vendor patches now available. No public exploit code or CISA KEV listing has been identified at time of analysis.
Technical ContextAI
The SMB (Server Message Block) protocol is Windows' primary file and printer sharing protocol, implemented in the kernel-mode driver srv2.sys. CWE-122 (Heap-based Buffer Overflow) indicates that attacker-controlled data exceeds the bounds of a heap-allocated buffer, enabling overwrite of adjacent heap metadata or function pointers. This class of flaw in a kernel-mode network service is particularly dangerous because successful exploitation can achieve SYSTEM-level code execution without any user-space boundary to cross. The vulnerability is present across a wide CPE surface: Windows 10 (21H2, 22H2, 1607, 1809), Windows 11 (23H2, 24H2, 25H2, 26H1), Windows Server 2012/2012 R2, 2016, 2019, 2022, and 2025 - including Server Core installations.
RemediationAI
Apply the Microsoft security update corresponding to the affected Windows build immediately, targeting the specific fixed build numbers listed per version above (e.g., Windows Server 2025 to 10.0.26100.33296 or later, Windows 11 24H2 to 10.0.26100.9168 or later). The vendor advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62800 provides the authoritative patch mapping. If immediate patching is not feasible, block inbound SMB traffic (TCP 445, UDP 137-138, TCP 139) at the network perimeter firewall to prevent external exploitation - note this does not address lateral movement risk from already-authenticated internal attackers. Additionally, restrict SMB access via host-based firewall rules to only systems that require it, and audit accounts with network logon rights to reduce the PR:L attack surface. Disabling SMBv1 (already deprecated) does not mitigate this vulnerability if SMBv2/3 remains enabled.
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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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