EUVD-2026-56669
GHSA-5jh2-2f4m-vpvc
Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Network-reachable SMB flaw requiring low-privilege credentials; full RCE impact justifies C:H/I:H/A:H with no scope change.
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 is achievable in Windows SMB Server via a heap-based buffer overflow exploitable by a low-privileged, authenticated network attacker. The vulnerability (CWE-122) spans a wide range of Microsoft Windows client and server releases from Windows Server 2012 through Windows Server 2025 and Windows 10/11. Microsoft has released patches via the MSRC update guide; no KEV listing or public exploit code is present in the available intelligence at time of analysis.
Technical ContextAI
SMB (Server Message Block) is Microsoft's proprietary network file-sharing and inter-process communication protocol, integral to Windows networking and present in virtually all Windows deployments. CWE-122 (Heap-based Buffer Overflow) identifies the root cause: the SMB server fails to validate the size of attacker-controlled input before writing it into a heap-allocated buffer, allowing data to overflow into adjacent memory regions. Successful exploitation of heap overflows can enable control-flow hijacking and arbitrary code execution in the context of the SMB server process, which runs with elevated system-level privileges. The CVSS vector AV:N/AC:L/PR:L/UI:N confirms the vulnerability is reachable over the network, requires no user interaction, and has low access complexity - meaning exploitation is repeatable and scriptable once the attacker holds valid credentials.
RemediationAI
The primary remediation is to apply Microsoft's released security updates via Windows Update or WSUS, targeting the minimum fixed build numbers per platform as listed in EUVD-2026-56669 and the MSRC advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-62790. Fixed build thresholds include Windows Server 2025 at 10.0.26100.33296, Windows Server 2022 at 10.0.20348.5499, Windows Server 2019 at 10.0.17763.9115, Windows Server 2016 at 10.0.14393.9418, Windows 10 22H2 at 10.0.19045.7663, and Windows 11 23H2 at 10.0.22631.7517 among others. Where patching cannot be applied immediately, compensating controls include restricting inbound SMB (TCP port 445) at network perimeters and host-based firewalls to only explicitly required sources - noting that this may disrupt file sharing and domain authentication workflows. Disabling SMBv1 entirely is advisable on any environment still running it, though this CVE affects the SMB server component broadly. Windows Server 2012 and 2012 R2 are in extended security update status; organizations on those versions should verify ESU enrollment or accelerate migration. No generic 'defense-in-depth' compensating controls are appropriate as a substitute for patching given the low attack complexity.
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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
Leaving vuln.today