CVE-2025-47999: Hyper-V DoS Patch Guidance for Adjacent Attacks

Microsoft’s advisory language and third‑party tracking show that the widely reported Hyper‑V flaw you referenced is cataloged as CVE‑2025‑47999, not CVE‑2025‑49751 — the difference appears to be a typo — and it describes a missing synchronization bug in Windows Hyper‑V that can be weaponized by a locally‑adjacent, authorized attacker to cause a denial‑of‑service (DoS) condition on affected hosts and virtualized workloads. (nvd.nist.gov) (cvedetails.com)

Background​

Windows Hyper‑V is a core virtualization technology used on Windows client and server platforms and in many cloud stacks. When a hypervisor component fails to correctly coordinate concurrent access to shared internal data structures — a class of defects categorized as CWE‑820: Missing Synchronization — the result can be race conditions that crash services or render virtualization management unstable.
Vendor and public vulnerability trackers describe this issue as a DoS that is reachable from an adjacent network with low privileges required and no user interaction; Microsoft published the advisory and NVD and vulnerability databases have ingested the record and vendor references. (nvd.nist.gov) (cvedetails.com)

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What the record actually says (concise, verifiable facts)​

• The authoritative entry in the National Vulnerability Database lists the vulnerability as CVE‑2025‑47999 with the description: “Missing synchronization in Windows Hyper‑V allows an authorized attacker to deny service over an adjacent network.” (nvd.nist.gov)
• Public vulnerability aggregators corroborate the same summary and enumerate affected Windows builds and SKUs (Windows 10/11 and Windows Server branches up to specific build numbers prior to vendor updates). (cvedetails.com)
• The CVSS v3.1 base score recorded by the CNA (Microsoft) is 6.8 (MEDIUM) with vector AV:A/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H — meaning the attack is adjacent network and requires low privileges but primarily impacts availability. (nvd.nist.gov)
• Vendor guidance indicates a security update is available; administrators should apply the supplied Microsoft update to remediate the defect. The NVD and aggregator entries reference the Microsoft Security Update Guide and the advisories published there. (nvd.nist.gov, cvedetails.com)

(If you specifically reported CVE‑2025‑49751, that identifier does not appear in authoritative tracker listings; the record above is the one matching the technical summary you provided. Treat the CVE you sent as likely transposed digits — confirmation and authoritative remediation reference should use CVE‑2025‑47999.) (nvd.nist.gov)

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Why this matters to Windows administrators and cloud operators​

Hyper‑V isn’t an incidental component — it’s often the foundation of virtual infrastructure, developer workstations, nested test environments, and many cloud offerings. A DoS that targets the virtualization layer can have outsized operational impact:

• Service availability: Crashes of the Hyper‑V management stack or VM host instability can make dozens or hundreds of VMs unreachable, interrupting business services.
• Multi‑tenant impact: In shared hosting or cloud environments, an adjacent attacker (for example, another tenant on the same network segment) can potentially disrupt co‑tenants.
• Operational risk: Recovery steps such as forced reboots, VM failovers, or migration can impose downtime and operational costs; undocumented or faulty recovery behaviors can complicate incident response.
• Chaining potential: Even when a bug only provides DoS, attackers can use it tactically (distraction, cover for other intrusions, delaying detection or recovery).

Community‑facing discussions and early analysis emphasize those operational impacts and warn that Hyper‑V vulnerabilities are high‑impact even when they do not yield remote code execution. This is reflected in forum analyses and incident response advisories.

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Technical classification and attack profile​

Nature of the bug​

• Type: Missing synchronization (race condition) in Hyper‑V internals (CWE‑820). The vulnerable code path does not serialize access to a shared resource correctly, producing a timing window that can be forced into an invalid state. (nvd.nist.gov)

Attack vector and prerequisites​

• Attack vector: Adjacent network (AV:A). An attacker must be able to communicate on the same adjacent network as the target (this often includes some types of management VLANs, host‑VM network attachments, or shared virtual switches). (nvd.nist.gov)
• Privileges required: Low (PR:L) — the adversary needs only limited privileges on the network level, though in practice knowledge of the environment and reachable endpoints is needed. (nvd.nist.gov)
• User interaction: None required (UI:N). The exploit can be executed without prompting a user. (nvd.nist.gov)
• Impact: Availability only (A:H) — attackers can cause service interruption rather than data disclosure or integrity loss. (nvd.nist.gov)

Severity metrics​

• CVSS v3.1 base score: 6.8 (Medium). This score reflects the relative complexity and the primary availability impact; it is not classified as remote code execution. (nvd.nist.gov)
• EPSS / exploitation probability: Public aggregation shows a low short‑term EPSS/likelihood score for mass exploitation, but the practical risk to exposed multi‑tenant or poorly segmented environments is higher. Monitoring adoption of the patch is crucial. (cvedetails.com)

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Affected platforms (what to look for)​

Aggregators and vendor references enumerate a broad set of Windows client and server releases where Hyper‑V is present, with specific build thresholds indicating patched vs unpatched versions. Typical affected families include, but may not be limited to:

• Windows 10 (various LTS and feature updates) up to noted build numbers
• Windows 11 22H2 / 23H2 / 24H2 builds prior to the fixed builds
• Windows Server 2016, 2019, 2022, and Server 2025 builds prior to vendor updates

Exact build cutoffs are provided in vendor advisories and in vulnerability database entries; administrators must verify their installed build numbers against the vendor’s published fixed builds before concluding whether a host is vulnerable. (cvedetails.com, nvd.nist.gov)

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Immediate mitigation and remediation (practical, prioritized steps)​

Apply the following steps in the order shown to reduce exposure quickly and safely.

• Patch first
• Apply Microsoft’s Hyper‑V security update that corresponds to CVE‑2025‑47999 using your normal patch management process (Windows Update, WSUS, Microsoft Update Catalog, or your enterprise patching tool). Vendor advisories and NVD point to Microsoft’s Security Update Guide for the fix. (nvd.nist.gov, cvedetails.com)
• If immediate patching is not possible, reduce exposure
• Isolate management and VM networks: move Hyper‑V management interfaces and host‑only networks to dedicated VLANS that are not adjacent to user or tenant networks.
• Disable or restrict unneeded network adjacency: remove guest‑host bridged connections that are not essential.
• Harden access controls: ensure only trusted admin accounts can access hosts and management consoles; apply multi‑factor authentication for management.
• Audit and inventory
• Identify Hyper‑V hosts and the build numbers in your estate. Use inventory tools (SCCM/MECM, Intune, or PowerShell scripts querying WMI / Get‑ComputerInfo) to find hosts with vulnerable builds. Cross‑reference with the vendor advisory’s affected build list. (cvedetails.com)
• Monitor for indicators
• Enhance logging and watch for unusual Hyper‑V service crashes, vmms.exe restarts, or VM management RPC failures. Unexpected host reboots or sudden cluster failovers are high‑priority indicators.
• Tune SIEM to alert on Hyper‑V service faults and unexpected service restarts.
• Post‑patch validation
• Test patched systems in a staging environment to ensure functionality (live migration, checkpoints, virtual switch operations) before mass deployment.
• After patching, validate hosts are running the expected fixed build numbers.
• Consider disabling Hyper‑V where not used
• For developer workstations or machines that do not require virtualization, consider turning off the Hyper‑V role or virtualization features as a temporary hardening step.

These actions follow standard vendor recommendations: patch first, then use segmentation and least‑privilege controls to reduce the attack surface while the patch is rolled out. (nvd.nist.gov, cvedetails.com)

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Detection guidance and forensic hints​

Short‑term detection is focused on availability anomalies and Hyper‑V service behavior:

• Watch for these events and behaviors:
• vmms.exe crashes or unexpected termination in Windows Event Log (System/Application).
• Hyper‑V host reboots without administrator initiation.
• Mass VM state changes (sudden saved states, paused VMs, or failed live migrations).
• High incidence of network errors or dropped packets on virtual switches.
• Recommended queries and checks:
• Search host event logs for “Hyper‑V” service stoppages and WMI errors around the time of observed outages.
• Use cluster logs (if using failover clustering) to identify simultaneous host issues that could indicate a Hyper‑V stack fault.
• Monitor hypervisor‑related performance counters for abnormal spikes prior to a crash (CPU, memory pressure, VM switch I/O anomalies).

Note: Because this is a concurrency/race condition bug, there may not be a clear exploit artifact beyond the crash itself — root cause determination frequently depends on correlating timing, service fault dumps, and any network operations that preceded the failure.

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Longer‑term hardening and risk reduction​

Beyond immediate patching and network isolation, adopt these proven controls to reduce future exposure:

• Network segmentation and strict VLANing for management and tenant traffic.
• Keep hypervisor hosts minimal — avoid running additional services on the host OS; dedicated management hosts reduce attack surface.
• Role separation and least privilege for management accounts, and enable multi‑factor authentication.
• Regular vulnerability scanning of Hyper‑V hosts together with automated patch compliance checks.
• Implement immutable or versioned VM image pipelines so operators avoid the temptation to mount untrusted images on production hosts.
• Adopt defensive programming practices in your internal platform: enforce code reviews and concurrency testing for any in‑house drivers or extensions to the Hyper‑V stack.

Forum and community discussions reinforce that organizations often overlook network topology and host service segregation when evaluating Hyper‑V risk — fixing these architectural points reduces the likelihood that adjacent‑network vulnerabilities become high‑impact incidents.

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Critical analysis — strengths, unknowns, and risks​

Strengths in Microsoft’s handling​

• Microsoft published the advisory and fixes and the issue has been recorded in public vulnerability databases; the presence of a recorded CVSS vector and vendor advisory makes prioritization and patching straightforward. (nvd.nist.gov)
• The vulnerability’s classification as DoS (availability only) narrows the immediate risk profile compared with remote code execution or elevation‑of‑privilege bugs.

What remains uncertain or risky​

• Adjacency semantics: “Adjacent network” can mean different things in cloud, on‑prem, or nested virtualization setups. Environments with shared virtual switches or insufficient VLAN isolation are at significantly greater risk.
• Exploit complexity and weaponization: Race conditions can be subtle to exploit reliably; however, determined attackers may build stable triggers. Public trackers show low short‑term EPSS but do not eliminate targeted abuse risks. (cvedetails.com)
• Patch adoption lag: Historical telemetry shows enterprises can take weeks to months to fully adopt critical virtualization patches; unpatched hosts in that window are high‑value targets for opportunistic attackers. Community reporting and analysis emphasize the long tail of unpatched virtualization infrastructure.

Practical risk posture​

• For single‑tenant, well‑segmented datacenters with strong host controls, the operational risk is moderate once patches are applied.
• For multi‑tenant cloud providers, labs, or organizations that permit cross‑VM networking, the impact can be severe because an adjacent tenant could cause broad disruption.

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How to verify your environment is protected (checklist)​

• Confirm the CVE: ensure you are tracking CVE‑2025‑47999 (note possible typo in earlier reports). (nvd.nist.gov)
• Inventory all Hyper‑V hosts and record OS build/version numbers. (cvedetails.com)
• Cross‑check build numbers against Microsoft’s fixed KB entries and the Security Update Guide to confirm the host is on a fixed build. (nvd.nist.gov)
• Deploy the update to a staging ring, validate Hyper‑V functionality (live migration, replication, virtual switch behavior), and then roll out broadly.
• Monitor hosts post‑deployment for new or unresolved service events and adjust rollback procedures if unexpected application behavior appears.

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Final verdict and recommended timeline​

• Short term (0–72 hours): Immediately identify Hyper‑V hosts and schedule emergency patching for production hosts. If patching cannot be completed in 72 hours, implement network segregation and minimize adjacencies as a compensating control. (nvd.nist.gov, cvedetails.com)
• Medium term (1–3 weeks): Complete enterprise roll‑out of the update, verify remediation, and refine detection rules and runbooks for Hyper‑V service failures.
• Long term (1–3 months): Reassess Hyper‑V network design, enforce management network isolation, and incorporate Hyper‑V specific checks into vulnerability scanning and patch automation.

This approach balances the immediate imperative to reduce exposure with operational caution: test before mass deployment, but do not delay patching indefinitely.

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Microsoft’s advisory data and public vulnerability trackers make clear the defect is real, fixable, and operationally material — but manageable with disciplined patching and sensible network hardening. Administrators should treat “adjacent network” vulnerabilities as serious architecture issues and act quickly to both remediate and to harden network topology against future races and synchronization bugs. (nvd.nist.gov, cvedetails.com)

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Source: MSRC Security Update Guide - Microsoft Security Response Center