CVE-2026-57089 — Windows SMB Server Network Transport Driver (srvnet.sys) Remote Code Execution Vulnerability

Executive Summary

Use after free in Windows SMB Server Network Transport Driver (srvnet.sys) allows an unauthorized attacker to execute code over a network.

Overview

9.8

CVSS CRITICAL

Important

MS Severity

Not Exploited

MS Exploit Status

Exploitation Unlikely

MS Exploit Likelihood

Category Remote Code Execution

Weakness CWE-416: Use After Free

Released Jul 14 2026

Last Updated Jul 14 2026

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.0061 — 0.46185 percentile

NVD CVSS 9.8 CRITICAL — differs from MSRC

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

ATTACK VECTOR

Network

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

None

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 6.5

EPSS Score

0.0061

probability of exploitation in the next 30 days

0.46185 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

27 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 Version 1607 for 32-bit Systems	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1607 for x64-based Systems	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1809 for 32-bit Systems	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 1809 for x64-based Systems	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for 32-bit Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for ARM64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 21H2 for x64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for 32-bit Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for ARM64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 10 Version 22H2 for x64-based Systems	`5099539 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 24H2 for x64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 25H2 for ARM64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 25H2 for x64-based Systems	`5101650 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 Version 26H1 for ARM64-based Systems	`5101649 (Security Update)`	Important	Remote Code Execution	Yes
Windows 11 version 26H1 for x64-based Systems	`5101649 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2012	`5099445 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2012 (Server Core installation)	`5099445 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2012 R2	`5099444 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2012 R2 (Server Core installation)	`5099444 (Monthly Rollup)`	Important	Remote Code Execution	Yes
Windows Server 2016	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2016 (Server Core installation)	`5099535 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2019	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2019 (Server Core installation)	`5099538 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2022	`5099540 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2025	`5099536 (Security Update)`	Important	Remote Code Execution	Yes
Windows Server 2025 (Server Core installation)	`5099536 (Security Update)`	Important	Remote Code Execution	Yes

Patches

9 patches

Article	Type	Restart
`5099535`	Security Update	Yes
`5099538`	Security Update	Yes
`5099539`	Security Update	Yes
`5101650`	Security Update	Yes
`5101649`	Security Update	Yes
`5099445`	Monthly Rollup	Yes
`5099444`	Monthly Rollup	Yes
`5099540`	Security Update	Yes
`5099536`	Security Update	Yes

Patch Diff

ghidriff · srvnet.sys (KB5101650)

Use-after-free (CWE-416) in the Windows SMB Server Network Transport driver srvnet.sys endpoint/connection lifecycle, unauthenticated remote code execution over the network. srvnet.sys is the SMB server's kernel network transport; SMB endpoints/connections are torn down by SrvNetTdiCloseConnection / SrvNetCloseConnectionWithLock / SrvNetDeregisterClient while network data is delivered to them by the TDI receive handlers (SrvNetTdiReceiveHandler / SrvNetCommonReceiveHandler / SrvNetTdiReceiveCompletion). PRE: an SMB endpoint object could be closed and freed while a receive handler was still processing an in-flight receive on it - a race between connection teardown and network receive that yields a use-after-free of the endpoint. Because srvnet processes attacker-supplied SMB traffic over the network without authentication, the freed-object reuse is a remote code-execution primitive (AV:N; AC:H reflects winning the race). Diff of srvnet.sys 10.0.26100.8521 -> .8875 (Jul 14 2026, KB5101650) confirms the fix: gated behind CFR flag Feature_3107684665, the endpoint gains rundown protection (a rundown ref at endpoint+0x288) - SrvNetAllocateEndpointCommon calls ExInitializeRundownProtection on the new endpoint, the receive handlers ExAcquireRundownProtection before using the endpoint (and ExReleaseRundownProtection after), and SrvNetTdiCloseConnection calls ExWaitForRundownProtectionRelease + ExRundownCompleted before teardown - so the endpoint cannot be freed while a receive is in flight, closing the race/UAF.

Pre-patch version 10.0.26100.8521 Download

Post-patch version 10.0.26100.8875 Download

Function	Address	Change	Note
`SrvNetAllocateEndpointCommon`	`code change`	code (rundown protection initialized on the endpoint, CFR-gated)	Post (Feature_3107684665): ExInitializeRundownProtection(endpoint + 0x158/0x288) when allocating the endpoint.
`SrvNetTdiReceiveHandler / SrvNetCommonReceiveHandler`	`code change`	code (receive acquires rundown protection, CFR-gated)	Post: ExAcquireRundownProtection(endpoint + 0x288) before processing the receive (and ExReleaseRundownProtection after), so the endpoint is kept alive while a receive is in flight.
`SrvNetTdiCloseConnection`	`code change`	code (teardown waits for rundown release, CFR-gated)	Post: ExWaitForRundownProtectionRelease(endpoint + 0x288) then ExRundownCompleted(endpoint + 0x288) before tearing down, so close blocks until all in-flight receives release their reference.
`SrvNetCloseConnectionWithLock / SrvNetDeregisterClient / SrvNetUnpublishClientSlot / SrvNetEndpointReopenTdiConnections`	`code change`	code (endpoint lifecycle updated)	Related endpoint close/deregister/reopen paths updated to the rundown-protected lifecycle.
`Feature_3107684665`	`gate`	added (CFR gate)	Primary CFR flag gating the rundown-protected endpoint lifecycle (Feature_1180933432 also present); the original unprotected path still ships when disabled.

View full diff report View RCA report

Attack Path

An SMB endpoint is closed/freed while a network receive is still processing it, causing a UAF

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Exploits & PoC

No public exploit or PoC has been linked for this CVE yet. When available, references are sourced from public repositories and may be unverified or non-functional — review carefully before use.

Detection Rules

No public Sigma or Nuclei detection rule has been mapped to this CVE yet. Coverage is concentrated on exploited / high-profile vulnerabilities; check SigmaHQ for updates.

Acknowledgments

Microsoft

References

MSRC Advisory MITRE NVD