CVE-2025-62567: Hyper-V Integer Underflow DoS and Patch Guidance

CVE-2025-62567 is a newly recorded vulnerability in Microsoft’s Hyper‑V virtualization stack that has been flagged as a Denial of Service (DoS) condition caused by an integer underflow (wrap/wraparound); the entry is listed in public trackers and in Microsoft’s Security Update Guide, but vendor-published detail is intentionally minimal, leaving defenders to prioritize patch mapping and layered mitigations while technical researchers work toward a fuller root-cause disclosure.

Background / Overview​

Hyper‑V is Windows’ native hypervisor and one of the largest attack surfaces on modern Windows hosts because host-side components (kernel-mode Virtualization Service Providers, or VSPs) process inputs originating from lower-privileged contexts such as guest VMs and userland tools. A flaw in one of these kernel-mode components can create high-leverage primitives — ranging from denial-of-service to local privilege escalation — that threaten host stability and the confidentiality, integrity, and availability of all co-located VMs.
CVE-2025-62567 is described by public trackers as an integer underflow in the Hyper‑V code path that can be triggered to cause a DoS. The canonical vendor mapping for the CVE is the Microsoft Security Update Guide entry for CVE-2025-62567; however, Microsoft’s public advisory text for kernel-level issues is often brief and omits low-level exploit mechanics — a deliberate practice designed to reduce the immediate risk of weaponization before customers can apply vendor fixes.

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Why this vulnerability matters to Windows administrators​

• Kernel-mode VSP components execute with SYSTEM/kernel privileges. Any logic error in those components can cause system-wide instability or be used as a foothold for escalation.
• Hyper‑V hosts often run many production workloads (VDI, databases, domain controllers) on a single physical host — one compromised or crashed host can disrupt dozens or hundreds of VMs.
• The vulnerability class (integer underflow) is a memory-safety family that may produce predictable corruption or bounds calculation errors; those errors may be exploited for resource exhaustion, out-of-bounds operations, or state inconsistencies that crash the kernel. Public advisories for this CVE currently report Denial of Service as the primary impact.

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What we know now — verified facts and discrepancies​

• Summary classification: Integer underflow (CWE‑191) in Hyper‑V leading to Denial of Service. This characterization is present in widely used vulnerability trackers.
• Vendor entry: Microsoft’s Security Update Guide lists CVE‑2025‑62567 as the authoritative record for KB/build mapping and remediation guidance; the MSRC page must be used to determine the exact updates for each affected Windows SKU. The MSRC entry is the canonical remediation source even when it is terse on technical detail.
• CVSS / severity: Third‑party trackers report a CVSS v3.1 base score around 5.3 (Medium) for this CVE, but scoring can vary across aggregators. The publicly visible CVSS vector observed on some feeds suggests network‑facing attack vector with limited privileges required; this is notable and requires careful confirmation against Microsoft’s KB mapping and NVD/MITRE records before operational conclusions are drawn.
• Exploit status: At the time of writing there are no widely published, reliable proof‑of‑concept exploits for CVE‑2025‑62567 in major public feeds; vendor materials have not claimed active exploitation. That reduces near-term mass-exploitation pressure but does not eliminate the risk that a PoC will appear quickly. Cybersecurity industry roundups that list December 2025 Patch Tuesday changes include CVE‑2025‑62567 among updated Hyper‑V/DOS items, underscoring the need to treat it as actionable.

Caveat: public trackers sometimes differ on attack vector and remotely exploitable flags. One common point of confusion for Hyper‑V CVEs is whether a vulnerability can be triggered remotely from an untrusted network or requires some form of local/guest access. For CVE‑2025‑62567, some feeds show a network vector while simultaneously labelling “Remotely Exploit: No” — a contradiction that must be resolved by consulting the Microsoft Security Update Guide and the exact KB text for the affected component and build. Treat any attacker-vector claim as provisional if it is not directly corroborated by Microsoft’s KB or by at least two reputable trackers.

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Anatomy: integer underflow in virtualization code — why it breaks hosts​

An integer underflow occurs when an arithmetic operation reduces a variable below the representable range for its signed or unsigned type, often wrapping to a large positive value (unsigned) or causing other incorrect results. In Hyper‑V’s storage and integration stacks, integers are used to record buffer lengths, descriptor sizes, offsets, and loop counters. If an underflow flips a length to an unexpectedly large value, the driver can:

• allocate or read the wrong amount of data,
• perform out-of-bounds memory accesses,
• produce arithmetic that bypasses safety checks, or
• trigger resource exhaustion and kernel faults.

In kernel mode, these faults cause unhandled exceptions and Blue Screen (BSOD) conditions or kernel crashes, which manifest as availability attacks against the host. This is why memory-safety errors that may seem “benign” in user mode can be catastrophic when they occur in host-side virtualization drivers.
Practical exploitation paths for integer underflow in Hyper‑V typically require that an attacker or guest supply crafted payloads (VHD descriptors, IOCTL inputs, integration channel messages) that exercise the vulnerable arithmetic. The ease of exploitation depends on whether the vulnerable code is reachable from an unauthenticated network path, from a guest VM, or from a low‑privileged local process; each path has different operational implications for defenders.

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Cross‑referenced verification and the “confidence metric”​

To meet high standards of operational verification, every key claim about CVE‑2025‑62567 was checked against multiple sources:

• Microsoft’s Security Update Guide — the vendor anchor for CVE→KB mapping (MSRC entry is authoritative for remediation even when its text is terse).
• Public vulnerability aggregators and trackers — which recorded an integer underflow in Hyper‑V and gave a CVSS score around 5.3 while listing Denial of Service as the impact. These trackers reported the CVE on the December 9, 2025 feed.
• Industry patch roundups and news — which list CVE‑2025‑62567 among December Patch Tuesday Hyper‑V fixes and emphasize immediate patching priority for Hyper‑V hosts. These sources confirm vendor updates and operational urgency but do not add low-level exploit detail.

Where a specific technical claim could not be verified from at least two independent, authoritative sources (for example, the exact IOCTL, call stack, or exploit primitive), that claim is flagged as unverified in the text. This cautious approach prevents overconfident statements about exploitability or weaponization that could mislead defenders.

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Who should care most — prioritized risk model​

• Hosting providers, cloud operators, and multi‑tenant Hyper‑V farms — a single host crash or exploit can impact many tenants and services.
• Enterprises running production VMs on Hyper‑V hosts (domain controllers, databases, jump boxes) — elevated host risk translates to domain‑wide exposure.
• Management/jump hosts and developer/test machines where semi-trusted VHDs or untrusted images are mounted — these often provide easier footholds for attackers.

Lower priority but still material: individual desktop Hyper‑V users who run untrusted VMs — depending on the threat model, they may be less likely targets but still benefit from patching.

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Immediate operational playbook (0–72 hours)​

These are practical, risk‑based steps designed to enable calm, correct action in production environments. Patch mapping from Microsoft’s Security Update Guide is the center of the plan.

• Inventory and identify (0–6 hours)
• Use configuration management tools (SCCM / WSUS / Intune / PowerShell) to enumerate Hyper‑V hosts, host builds, and storvsp/sys or related driver versions. Map the OS build numbers to Microsoft’s CVE→KB mapping before any mass deployment.
• Pilot test (6–24 hours)
• Retrieve the specific KB(s) Microsoft lists for the affected builds and apply them to a representative pilot group that includes cluster nodes, VDI hosts, and management jump boxes. Test live migration, replication, backups, and VM stability thoroughly.
• Staged deployment (24–72 hours)
• Roll updates to production hosts in prioritized waves: hosting → VDI → admin servers → endpoints. Schedule reboots in maintenance windows because kernel/driver updates require reboots. Validate driver versions and that host crashes no longer reproduce after patching.
• Short-term compensating controls if patching is delayed
• Restrict who can mount or attach VHD/VHDX images and disable nonessential guest‑host integration features. Segment Hyper‑V management, live migration, and storage traffic on separate VLANs or fabrics. Reduce interactive logons on hosts and enforce least privilege for service accounts.
• Update detection content
• Apply vendor IDS/IPS/EDR signatures and vendor advisories that correlate to Hyper‑V attack patterns; tune detection rules for DeviceIoControl/IOCTL anomalies and unexpected storvsp.sys exceptions.

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Detection, hunting, and incident response​

Detection in cases of kernel crashes and DoS does not rely on classic IOCs alone — focus on behavior and artifacts:

• Hunt signals: repeated or unexpected BSODs referencing storvsp.sys (or Hyper‑V storage stacks), unexpected vmms.exe crashes or restarts, unusual DeviceIoControl activity, repeated VHD attach/unattach operations by non‑admin users.
• Forensic capture: if exploitation is suspected, preserve memory dumps, WER minidumps, Windows Event logs, driver lists, and recent device attach logs before rebooting the host. Kernel state is volatile and valuable for root-cause triage.
• Containment: isolate affected hosts, halt VM migrations that might spread impact, and rotate high‑value credentials that were active on compromised hosts if there is evidence of deeper compromise. Treat suspected kernel compromise as high severity and preserve artifacts for incident response teams.

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Critical analysis — strengths, weaknesses, and risks​

Strengths (defensive posture)​

• Vendor acknowledgement in the Microsoft Security Update Guide provides a clear remediation path and authoritative KB mapping; that alone makes the risk actionable. Microsoft’s entry is the canonical source for which builds and KBs to install.
• Industry patch roundups and vendor detection content are being produced in parallel with the advisory, giving defenders short-term detection options while patches are validated.

Weaknesses / Unknowns​

• Sparse public technical detail: Microsoft’s public advisory for kernel vulnerabilities typically omits IOCTLs, call stacks, and exploit mechanics. That leaves defenders dependent on black-box patching rather than targeted mitigations. This reduces the ability to craft precise detection rules.
• Conflicting metadata across aggregators: some trackers indicate a network attack vector while simultaneously marking “Remotely Exploit: No.” These contradictions must be resolved by consulting Microsoft’s KB text and by vendor telemetry. Until then, operational decisions should default to a conservative posture (assume broader reach).

Potential operational risks​

• Multi‑tenant hosts and cloud providers face the highest consequences: a single exploit or host crash can affect many tenants and increase legal/compliance impact.
• If a PoC appears and demonstrates a reliable crash or exploitation path, attackers can weaponize the primitive quickly — the defensive window between disclosure and PoC publication is typically short for Hyper‑V primitives. History shows these primitives rapidly escalate from information disclosure to usable exploit chains in targeted intrusions.

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Long-term hardening recommendations​

• Enforce least privilege and minimize the set of users allowed to operate Hyper‑V hosts and mount virtual disks.
• Use network segmentation and dedicate management networks for Hyper‑V control, live migration, and storage traffic.
• Enable virtualization-based security features where hardware supports them (HVCI / Memory Integrity) to raise the bar for kernel exploitation. Maintain strict driver signing policies and Vulnerable Driver Blocklists.
• Regularly validate patch management pipelines and test kernel/driver updates in pilot rings to catch regressions before wide deployment.

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Final assessment and guidance​

CVE‑2025‑62567 is a vendor‑recorded Hyper‑V vulnerability characterized as an integer underflow that can cause Denial of Service. Because Microsoft’s Security Update Guide is the authoritative mapping for remediation, administrators must use that entry to identify the exact KBs for each host build and deploy patches in a staged, tested fashion. Public trackers and industry roundups corroborate the DoS classification and urge immediate patching of Hyper‑V hosts, but low-level exploit mechanics remain unpublished and should be treated as unknown until vendor or independent researcher analysis provides additional detail. Conservative, practical next steps:

• Map every Hyper‑V host and confirm the correct KB for each OS build using the Microsoft Security Update Guide.
• Test updates in a pilot ring and validate storage/VM functionalities.
• Deploy patches in prioritized waves and apply compensating controls (restrict VHD mounts, isolate management networks) if remediation must be delayed.

No public PoC has been widely published at this time, but the history of Hyper‑V vulnerabilities shows that the risk window can close quickly. Prioritize patching and layered mitigations, maintain robust detection and forensic readiness, and treat Microsoft’s update mapping as the single source of truth for remediation.

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CVE‑2025‑62567 is a clear reminder that virtualization-layer code must be treated as high‑value attack surface; its mitigation requires rapid, methodical patching, operational segmentation, and improved defender telemetry to stay ahead of exploit development and protect critical virtualized infrastructure.

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Source: MSRC Security Update Guide - Microsoft Security Response Center