CVE-2025-54091: Windows Hyper-V Local Privilege Escalation via Integer Overflow

CVE-2025-54091 — Windows Hyper‑V integer overflow / wraparound (local elevation of privilege)​

Summary (one‑line)​

An integer overflow or wraparound in a Windows Hyper‑V component can be triggered by an authorized local actor and may lead to local elevation of privilege (EoP) on the Hyper‑V host.

Why this matters​

• Hyper‑V runs at high privilege on Windows hosts; a local EoP that escapes a guest or abuses Hyper‑V management channels can allow an attacker to obtain SYSTEM/host privileges, tamper with other VMs, steal credentials, or persist on the host.
• Although the attack requires local/authorized access (for example, a process running on the host or code inside a guest that can interact with Hyper‑V channels), such flaws are frequently used in multi‑stage intrusions: initial access → local privilege escalation → full host/tenant compromise.

What the vendor (Microsoft / MSRC) says​

The Microsoft Security Response Center (MSRC) hosts the canonical advisory page for CVE-2025-54091 at the Update Guide URL you provided. That advisory is the authoritative source for the exact affected Windows builds, KB numbers, and whether updates are available for specific platforms; administrators should follow the MSRC guidance and the Microsoft Update Catalog for official KB identifiers before taking remediation actions. Note: MSRC’s Update Guide is driven by client‑side rendering/JavaScript, so automated scrapers may not show the full details — open it in a browser and record the KB/build list for your patching runbook.

Technical overview (what the bug is, at a systems level)​

• Class: Integer overflow / wraparound in Hyper‑V code path(s) that process guest‑controlled or external metadata. The overflow/wraparound can cause miscomputed lengths or indices used for memory allocations or copies, producing out‑of‑bounds writes (heap or stack) or logic bypasses.
• Attack vector: Local/authorized. Exploitation typically requires the attacker to be able to interact with a Hyper‑V component — for example, mounting a specially crafted VHD/VHDX image, sending crafted descriptors to device/driver parsers, or using a guest↔host integration channel. This “authorized” wording in vendor summaries indicates the attacker already has some local access on the machine or has a foothold in a guest VM.
• Likely impact: local privilege escalation to SYSTEM/host; secondary outcomes can include guest escape, kernel memory corruption, or denial‑of‑service (host/VM crash). The common exploitation pattern for integer overflow/wraparound problems is: an attacker supplies a large or specially chosen numeric field → code truncates or wraps the value when computing an allocation or copy length → a smaller-than-expected buffer is allocated → attacker-controlled data is copied and overflows into nearby control data (function pointers, vtables, heap metadata) → attacker pivots to code execution at high privilege.

What we could and could not verify (important)​

• Verified: MSRC lists an advisory for CVE‑2025‑54091 at the Update Guide URL you supplied (the page renders dynamically). The MSRC advisory is the definitive vendor source for affected builds and the fixed KBs.
• Not (yet) verified in public CVE/NVD mirrors: at the time of this write‑up, many third‑party and machine‑readable vulnerability databases either lag or have not yet published a full NVD/MITRE/NVD enrichment entry for this exact CVE identifier. Public trackers for related Hyper‑V CVEs show similar memory‑safety patterns, but do not necessarily contain the exact affected build list for CVE‑2025‑54091 — so do not rely on secondary mirrors for the final KB numbers. Cross‑check MSRC and Microsoft Update Catalog for authoritative patch identifiers before patching. (nvd.nist.gov)

Exploitation scenario(s) — realistic and practical​

• Guest‑to‑host escalation: an attacker running in a VM that can present a virtual disk or other descriptor to the host crafts a malformed VHDX (or device descriptor) that contains a numeric field sized to trigger an integer wrap. When the host parses or mounts the image, the miscomputed allocation leads to a heap corruption that the attacker converts into code execution in the host context. From there the attacker elevates to SYSTEM and can access other VMs and host artifacts.
• Local user escalation: a low‑privileged user on the host who is permitted to mount VHDs or interact with Hyper‑V device installers uses a specially crafted file or INF to trigger the overflow and obtain SYSTEM.

How to prioritize (risk triage)​

• Highest priority: production Hyper‑V hosts (cluster nodes, management/console servers), cloud/hosting nodes, backup or imaging servers that mount guest disks, and any host that accepts user‑supplied VHD/VHDX images.
• Medium priority: developer laptops or workstations where Hyper‑V is enabled but not used for multi‑tenant hosting. Still patch, but these are less likely to be targeted for large multi‑tenant impact.

Immediate recommended actions (0–24 hours)​

• Confirm the MSRC advisory and collect KB/build numbers for CVE‑2025‑54091 in your environment. The MSRC Update Guide is authoritative — use it to map KBs to your OS/builds.
• Identify all systems running the Hyper‑V role. Example PowerShell to inventory hosts at scale (run from an admin machine with appropriate credentials):
• Single host: Get‑ComputerInfo | select CsName, OsName, OsBuildNumber
• Detect Hyper‑V role: Get‑WindowsFeature -Name Hyper‑V*
• Enterprise inventory (SCCM/MECM/Intune): query role flag or run a script to collect WindowsFeature status and build numbers.
• Patch the highest‑value hosts first (production Hyper‑V clusters, management hosts) as soon as the KB is confirmed for your build. Test the patch in a staging cluster if you have production live migration / cluster constraints.

Short‑term mitigations if you cannot patch immediately​

• Isolate management networks: ensure Hyper‑V host management, live migration, and storage networks are on dedicated VLANs/fabrics inaccessible from general user/tenant networks.
• Restrict who can mount virtual disks / import device descriptors: only trusted administrators and service accounts should have these privileges. Remove the ability to mount user‑supplied VHDs on production hosts.
• Disable Hyper‑V on endpoints that don't need it (developer laptops, test machines) until patched: on Windows 10/11 you can turn off the platform feature or remove the role. (Note: this may require a reboot and could impact VMs/containers).
• If your environment ingests untrusted images, implement image validation (only accept signed images, scan in isolated sandbox hosts, avoid mounting directly on production hosts).

Detection and monitoring guidance​

Tune detection to the following high‑value indicators:

• vmms.exe or Hyper‑V service crashes / unexpected restarts (Hyper‑V Management Service restarts are high‑priority). Monitor service stop/start events and correlated host reboots.
• Unusual mount/unmount patterns for VHD/VHDX by non‑admin accounts, or rapid, repeated integration channel traffic from a guest.
• Sudden creation of snapshots, unexpected VM configuration changes, or new VM images appearing on hosts.
• SIEM rules: alert on EventLog entries showing privilege elevation attempts immediately after Hyper‑V service anomalies. Also watch for patterns of repeated RPC or integration channel operations.

Forensics / Indicators of Compromise (IOCs)​

• Kernel memory corruption traces in host crash dumps (windbg analysis may reveal unexpected control flow or overwritten function pointers in Hyper‑V components).
• Newly created SYSTEM‑level processes spawned by previously low‑privileged accounts.
• Suspicious accesses to VHD/VHDX files by accounts/processes that shouldn’t have them.

Developer / engineer guidance (if you maintain Hyper‑V‑related code)​

• Validate all integer inputs that determine allocation lengths; use 64‑to‑32‑bit conversion checks, saturating arithmetic, and explicit overflow detection APIs rather than relying on implicit truncation.
• Fail closed on parsing errors: do not trust malformed metadata (VHD headers, INF descriptors, device manifest fields) and perform multi‑stage validation (parse in low‑privilege, sandboxed process; then re‑validate before any privileged action).
• Add long‑running fuzzing and memory‑safety testing in CI for parsers that handle on‑disk formats (VHD/VHDX, vendor device descriptors).

PowerShell examples (inventory & quick checks)​

• Check if Hyper‑V role is installed on this host:
  Get‑WindowsFeature -Name Hyper‑V | Format‑Table -AutoSize
• List installed Windows build and OS:
  Get‑ComputerInfo | Select‑Object CsName, OsName, OsBuildNumber
• Check for hosts with Hyper‑V enabled across a domain (requires remoting / inventory): run a script via your management tool (SCCM/Intune) to run the above commands and aggregate results.

Patch testing and post‑patch validation​

• Test patch in a staging cluster that mirrors production Hyper‑V roles (live migration, cluster behavior, backup/restore, virtual switch connectivity).
• After patching: verify host OS build and KB identifiers match MSRC’s fixed build list; validate live migration, snapshotting, and backup jobs to confirm no regressions.

Cross‑checks and independent sources (what I used to compile this)​

• Microsoft’s MSRC/Update Guide advisory is the authoritative vendor resource for CVE‑2025‑54091 and must be used to map KBs to builds. Administrators should open the MSRC page in a browser and copy the KB/build list into their patching systems rather than relying on third‑party mirrors.
• Community and vendor trackers consistently describe Hyper‑V integer/heap problems as local/authorized EoP issues and provide practical runbooks (inventory, isolate management fabric, patch quickly). These practices and mitigations are echoed across multiple sources.
• Note on public CVE trackers: NVD and other public aggregators sometimes lag; at the time of this write‑up some NVD pages for nearby CVE IDs showed partial information. This is why cross‑checking the vendor advisory + Microsoft Update Catalog is essential for patch IDs and fixed build cutoffs. (nvd.nist.gov) (wiz.io)

Suggested operational checklist (concise)​

• Open MSRC CVE‑2025‑54091 advisory; record KB(s) and affected builds.
• Inventory all hosts running Hyper‑V (SCCM/Intune/PowerShell).
• Patch production Hyper‑V hosts first; test in staging.
• If you cannot patch immediately: isolate management networks; restrict who can mount images; disable Hyper‑V where unnecessary.
• Tune SIEM alerts for vmms.exe crashes, abnormal VHD mounts, and privilege elevation attempts.

If you want, I can (pick one)​

• Pull the exact KB/build list from MSRC and format it into an SCCM/WSUS deployment plan (I’ll need the MSRC advisory open or the KB numbers you want targeted).
• Produce a PowerShell script to inventory Hyper‑V hosts across your domain and flag out‑of‑date builds so you can prioritize patching.
• Create SIEM detection rules (example Splunk/Elastic/QRadar queries) for the indicators above.

Final notes / caution​

• Treat MSRC as the source of truth: do not rely solely on third‑party mirrors for KB IDs or fixed‑build cutoffs. MSRC’s advisory and the Microsoft Update Catalog should drive your patching and compliance evidence.
• Because the vulnerability requires local/authorized access, the most effective organizational mitigations (network segmentation, least‑privilege controls around who can mount/ingest virtual disks, and robust patch management) will materially reduce risk while you deploy fixes.

Sources referenced while preparing this briefing​

• Microsoft Security Response Center (MSRC) Update Guide entry for CVE‑2025‑54091 (vendor advisory / KB mapping).
• Community/analysis and runbooks for Hyper‑V integer/heap vulnerabilities (technical behavior, exploitation chains, and mitigations).
• Operational detection and patch‑priority guidance aggregated from community trackers and incident playbooks.
• Note on public CVE/NVD lag and verification best practice: backups from public trackers and NVD example pages illustrating enrichment delays. (nvd.nist.gov, wiz.io)

If you’d like, I can now:

• fetch the MSRC advisory and extract the KB numbers / affected builds into a ready‑to‑import CSV for SCCM/WSUS; or
• produce the PowerShell inventory + remediation script tailored to your environment (I’ll need the scope: AD domain, management tool, or a list of hostnames/IPs).

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Source: MSRC Security Update Guide - Microsoft Security Response Center