Microsoft and multiple vulnerability trackers recorded CVE-2025-62467 on December 9, 2025 — an
integer overflow / wraparound bug in the Windows
Projected File System (ProjFS) that can be abused by an authorized local user to gain elevated privileges, and which is currently rated
High (CVSS 3.1 = 7.8) in public feeds.
Background / Overview
The Windows Projected File System (commonly called
ProjFS) is a kernel-facing file-system projection API that lets a user-mode provider present hierarchical data from a backing store as ordinary files and folders on disk. ProjFS is used in scenarios that include virtual file systems and on‑demand content presentation (for example, VFS for Git and similar providers); it sits at a privileged boundary and receives callbacks and data from user-mode providers and clients. Because ProjFS mediates user→kernel transitions and deals with file metadata and I/O context, bugs in its kernel or driver-layer components are high-value targets for privilege-escalation research. CVE-2025-62467 is described in public vulnerability feeds as an
integer overflow or wraparound in the Projected File System that allows a local, authorized attacker to escalate privileges to a higher context (the public descriptors map the weakness to CWE-190 and CWE-126). That high-level characterization — integer overflow leading to buffer miscalculation and out-of-bounds memory access — is consistent with prior Projected File System and filesystem driver vulnerabilities where numeric miscalculations convert into memory-corruption primitives that yield kernel-level impact.
What the advisory actually confirms
- The vulnerability exists in the Windows Projected File System and is classified as Elevation of Privilege (EoP).
- Public trackers list the technical class as integer overflow / wraparound (CWE-190) and often associate an out-of-bounds read condition (CWE-126) with the bug.
- The public CVSS 3.1 base score in multiple aggregators is 7.8 (High) with an attack vector indicating local exploitation requiring low privileges.
- The vendor (Microsoft) has an Update Guide entry for the CVE for mapping to KB packages and updates; the MSRC Update Guide is the canonical remediation source. (Note: the vendor page is a dynamic web app; administrators should use the Update Guide to derive KB mappings.
These are the load-bearing, verifiable facts defenders must act on: the bug exists, it is high-impact (local EoP), and Microsoft lists the CVE in its update index for administrators to map to the correct updates.
Technical analysis — how an integer overflow in ProjFS becomes dangerous
Integer overflow → memory error → privilege conversion (high-level)
An
integer overflow or wraparound occurs when arithmetic on a fixed-size integer (for example, a 32-bit length or offset) exceeds the type’s capacity and wraps to a smaller value. In file-system code paths this can cause:
- allocation of a buffer that is too small for the intended data,
- computed copy lengths that exceed allocated sizes, or
- loop counters and bounds checks that are bypassed due to incorrect arithmetic.
When that condition happens in kernel code that handles user-supplied metadata (file lengths, projected file sizes, directory enumeration counts, or provider-supplied buffers), the result can be an
out-of-bounds read or
out-of-bounds write, which are classic memory‑corruption primitives. Those primitives can be escalated to full SYSTEM control by converting memory corruption into token manipulation, arbitrary kernel writes, or object overwrite patterns. Public CVE descriptors associate CVE‑2025‑62467 with both integer overflow (CWE‑190) and buffer over‑read (CWE‑126), which fits this exploitation model.
Why ProjFS is a privileged target
ProjFS operates at the intersection of user-mode providers and kernel-mode file-system plumbing. Key risk amplifiers:
- ProjFS interacts with both user-supplied data and kernel resources. A malicious or compromised provider can feed crafted metadata or I/O contexts into privileged callbacks.
- Kernel-side logic frequently performs arithmetic on size/offset fields that originate from or are influenced by provider state; a single unchecked length calculation can cause wraparound.
- Because ProjFS is implemented as a virtualizing component that may expose complex structures (directory entries, placeholder metadata, extended info), the attack surface includes multiple fields and code paths that historically have been susceptible to parsing and arithmetic errors.
These general technical properties match how earlier ProjFS and filter-driver vulnerabilities have been weaponized — an attacker with local code execution or a malicious provider can trigger the flawed logic and convert the memory corruption into an EoP primitive.
Exploitability and preconditions
Public records indicate the attack is
local and requires an
authorized user ability — that is, an attacker needs to run code on the target host (even as a non‑privileged user) or influence a ProjFS provider installed on the system. There are two common preconditions in real-world models:
- A local foothold (malware, malicious binary, or a user tricked into running code).
- The ability to interact with a ProjFS virtualization root or provider (for example, calling the provider interface, enumerating projected files, or invoking callback paths the provider uses).
Because the exploit vector is local, defenders often miss its urgency — but history shows that EoP bugs are the preferred second-stage tool for attackers who already have a foothold. That means the practical risk is high in environments where untrusted code can run (developer workstations, VDI endpoints, multi-user hosts).
Affected platforms, patching status, and practical remediation
What administrators must assume right now
- The vulnerability was publicly recorded on December 9, 2025 and is indexed in mainstream vulnerability feeds with a High severity rating. Administrators should assume their inventory may include affected builds until proven otherwise.
- The Microsoft Security Update Guide (MSRC) entry is the authoritative place to map CVE→KB for each Windows build and servicing channel; use that mapping to schedule and deploy updates. Microsoft lists the CVE in its Update Guide.
Patch-first posture
- Identify Windows hosts that have ProjFS or virtualization roots enabled (ProjFS is an optional component but is used by many providers such as VFS for Git and some cloud / sync providers).
- Map installed Windows builds and SKUs against the KB entries that MSRC lists for CVE‑2025‑62467 and schedule updates in your enterprise patching system (WSUS, SCCM/ConfigMgr, Intune, or the Microsoft Update Catalog).
- Pilot updates on a small ring that represents typical user workloads, validate behavior, then accelerate to high-value systems (domain controllers, admin workstations, build servers, VDI hosts).
Compensating controls when patching cannot be immediate
- Reduce local attack surface: remove administrative rights from standard users and restrict which accounts can perform interactive logons on high-value endpoints.
- Harden provider exposure: where feasible, disable or uninstall third-party ProjFS providers that are not required on servers and admin endpoints. If a provider is necessary, consider restricting its user context and updates.
- Application allow-listing: enforce WDAC / AppLocker to prevent untrusted local binaries from running on critical hosts. This reduces the chance of an attacker obtaining the initial foothold required to trigger a local EoP.
Detection, telemetry, and hunting guidance
Because CVE‑2025‑62467 is a kernel-level EoP with a local attack vector, network IDS rules are unlikely to detect exploitation attempts reliably; detection should focus on endpoint and kernel telemetry.
- Tune EDR rules to alert on unexpected SYSTEM-level process creations spawned from user-context processes (for example, cmd.exe, powershell.exe, or lsass-adjacent processes suddenly running as SYSTEM). This is a common post‑exploit indicator when a local EoP is weaponized.
- Monitor for DeviceIoControl/IOCTL anomalies directed at file-system filter or virtualization interfaces used by ProjFS providers; unusual or high-frequency IOCTL sequences from a single user process deserve attention.
- Watch for driver crashes or repeated WER/kernel logs that reference ProjFS components or the virtualization root: kernel oopses, bluescreens, or repeated restarts of related services indicate attempted triggers or failed exploit attempts. Preserve full memory dumps when you suspect exploitation for forensic analysis.
- Correlate process lineage with file-system events that touch virtualization roots; if a non-privileged process is repeatedly calling into ProjFS provider callbacks just before a SYSTEM elevation, treat this as high-priority.
Operational playbooks developed for other kernel EoP advisories apply well here: fast identification of candidate hosts, priority patching of admin/management endpoints, and high-fidelity EDR hunts for privilege escalation patterns.
Attack surface and realistic exploitation scenarios
- Developer laptops and build hosts that run ProjFS-backed tools (for example, VFS-style Git virtualization) are high-risk endpoints; attackers can often deliver unprivileged binaries to developer machines via phishing or compromised CI artifacts.
- Multi-user or shared VDI and remote desktop hosts: a single low‑privilege user on a shared host can attempt local escalation; prioritize patching these hosts.
- Environments that install provider components from third parties (custom ProjFS providers) introduce additional risk because compromised providers are a direct path into the kernel mediation logic. Consider auditing installed providers and their update mechanisms.
Strengths in the vendor response — and limitations defenders must accept
Notable strengths
- Microsoft recorded the CVE in the Update Guide and provides a canonical KB mapping process for remediation; vendor acknowledgement and a published update path are the most effective mitigations for kernel-level EoP bugs.
- Public vulnerability aggregators rapidly indexed the issue and assigned a CVSS, enabling vulnerability management tooling to prioritize affected assets. This improves enterprise readiness.
Limitations and residual risks
- Microsoft and vendor advisories commonly redact low‑level exploitation details for kernel bugs to reduce short-term weaponization risk. That means defenders must often act without full technical indicators of compromise and instead rely on behavioral detection and vendor KB mappings. Treat the absence of low‑level detail as an operational friction, not safety.
- At disclosure there may be no public proof‑of‑concept available; absence of a public PoC does not mean the vulnerability is not weaponized by sophisticated actors privately. Historical patterns show kernel EoP primitives are quickly converted into reliable post‑compromise tools once patch diffs or details appear. Treat unpatched hosts as high-priority even without public exploit code.
Step‑by‑step remediation playbook (recommended sequence)
- Inventory: query patch-management tools for systems with projected-file-system components, installed ProjFS providers, and user classes that run virtualization roots. Prioritize assets by administrative privilege exposure and their role in the network.
- Map: use Microsoft’s Security Update Guide to derive the exact KB(s) that address CVE‑2025‑62467 for every Windows build in your estate. Do not rely on CVE strings alone — confirm KB-to-Build mapping.
- Pilot: apply the update to a representative pilot ring (admin workstations, developer machines, VDI hosts). Validate application behavior and user workflows (especially any ProjFS-backed tooling).
- Deploy: roll out the update to high‑value systems (domain controllers, jump boxes, build servers) and then to broader endpoints. Coordinate reboots where necessary.
- Harden: apply application allow‑listing and reduce the number of users with persistent admin privileges. Where applicable, temporarily disable unneeded ProjFS providers on critical hosts until validated updates are applied.
- Monitor: tune EDR/SIEM to look for sudden SYSTEM process creation, IOCTL anomalies, and driver crash patterns. Preserve forensic artifacts for suspected exploitation.
Cross‑checks, validation, and claims to treat with caution
- Cross-reference of key claims: the CVE description and CVSS rating for CVE‑2025‑62467 appear in multiple independent trackers (public CVE aggregators and Patch-Tuesday coverage) and the vendor’s Update Guide is the canonical remediation source — that gives strong corroboration for the existence and high impact of the issue.
- Unverifiable or unconfirmed claims: any public statement asserting active in‑the‑wild exploitation tied specifically to CVE‑2025‑62467 should be treated as unverified until multiple telemetry sources (security vendors, MSRC telemetry, or CISA advisories) corroborate exploitation. There was no authoritative public PoC at initial disclosure; absence of a PoC does not equal safety.
Practical recommendations for teams now
- Treat CVE‑2025‑62467 as high-priority for patching when the applicable KB is identified for your builds. Vendor-supplied patches are the primary defense.
- Prioritize endpoints where local code execution is plausible: developer workstations, CI/build agents, VDI/RDP hosts, and any system that hosts third-party ProjFS providers.
- If you cannot patch immediately: remove unnecessary local admin rights, enable application allow‑listing, and restrict installation or use of third‑party ProjFS providers on critical assets. Tune EDR to detect SYSTEM elevation patterns and IOCTL anomalies for file-system filter/virtualization drivers.
Conclusion
CVE‑2025‑62467 is a credible, kernel-facing elevation-of-privilege vulnerability in the Windows Projected File System rooted in integer overflow/wraparound semantics. Public vulnerability trackers rate it
High (CVSS 7.8) and Microsoft’s Update Guide is the authoritative path for remediation mapping. Because ProjFS occupies a privileged mediation layer between user-mode providers and kernel I/O, a numeric error in its code paths can be converted into powerful local escalation primitives. The practical urgency is real: patch quickly, harden local privilege and provider exposure, and tune endpoint telemetry for behavioral signs of escalation while you complete rollout. If patching is delayed for operational reasons, rely on layered compensations — least privilege, allow‑listing, and monitoring — because history shows attackers will attempt to weaponize kernel EoP primitives once details (or patch diffs) become publicly available.
Source: MSRC
Security Update Guide - Microsoft Security Response Center