Severity by source
Sources disagree (Medium–Critical)AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Pre-auth network kernel RCE (PR:N, AV:N, full CIA impact), but AC:H because reliable use-after-free exploitation requires kernel heap grooming, consistent with SSVC 'Automatable: no'.
vuln.today treats the vendor’s rating as authoritative. A higher third-party CVSS (e.g. CISA-ADP) is shown for transparency but does not drive the headline severity.
CVSS VectorNVD
Lifecycle Timeline
6DescriptionNVD
Use after free in Windows SMB Server Network Transport Driver (srvnet.sys) allows an unauthorized attacker to execute code over a network.
AnalysisAI
Remote code execution in the Windows SMB Server Network Transport driver (srvnet.sys) allows unauthenticated network attackers to run arbitrary code by triggering a use-after-free condition, affecting a broad range of Windows client and server releases from Windows 10 1607 and Server 2012 through Windows 11 26H1 and Server 2025. Because the CVSS vector is AV:N/AC:L/PR:N/UI:N (9.8 Critical), exploitation needs no authentication or user interaction, giving this the structural profile of a wormable SMB flaw similar to prior srvnet.sys issues. No public exploit was identified at time of analysis and CISA SSVC lists exploitation as 'none', with a modest EPSS of 0.57% (43rd percentile).
Technical ContextAI
The vulnerability lives in srvnet.sys, the kernel-mode network transport driver that underpins the Windows SMB Server (LanmanServer) stack and handles SMB session and buffer management over TCP/445. The root cause is CWE-416 (Use After Free): the driver references a memory object after it has been freed, letting an attacker who controls the timing and content of freed/reallocated pool memory corrupt kernel state. Because srvnet.sys executes in kernel context, successful exploitation yields SYSTEM-level code execution rather than a user-space compromise. The affected CPEs span the full modern Windows lineage - Windows 10 (1607/1809/21H2/22H2), Windows 11 (24H2/25H2/26H1), and Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025 - indicating the defective code path is long-standing and shared across the SMB server implementation.
RemediationAI
Patch available per Microsoft advisory: apply the cumulative security update that raises each affected build to at or above its fixed version - for example Windows 11 24H2 to 10.0.26100.8875, Windows Server 2025 to 10.0.26100.33158, Server 2022 to 10.0.20348.5386, Windows 10 22H2 to 10.0.19045.7548, and the Server 2012/2012 R2/2016/2019 lines to the builds listed in the EUVD data - following the guidance at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-57089. Where immediate patching is not possible, reduce exposure by blocking inbound TCP/445 (and SMB) at the network perimeter and host firewall so SMB Server is unreachable from untrusted networks, restrict SMB access to trusted management VLANs, and disable the Server (LanmanServer) service on hosts that do not need to serve SMB shares. Trade-offs: blocking 445 or disabling LanmanServer breaks file/printer sharing, domain SYSVOL/NETLOGON access on domain controllers, and any application relying on SMB, so validate dependencies before applying these controls on servers.
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Same weakness CWE-416 – Use After Free
View allSame technique Use After Free
View allShare
External POC / Exploit Code
Leaving vuln.today
EUVD-2026-44269
GHSA-66gf-59r4-7c5w