Microsoft has assigned CVE-2025-62462 to a newly disclosed
buffer over‑read in the
Windows Projected File System (ProjFS) that can be abused by a local, authorized attacker to achieve
elevation of privilege; the industry score for the issue is high (CVSS v3.1 ≈ 7.8) and the entry appears in December 2025 vulnerability feeds and patch summaries.
Background / Overview
The Projected File System (ProjFS) is a kernel‑level file system filter used by Windows to implement cloud‑backed placeholders and other “projected” file views (OneDrive being the canonical example). ProjFS exposes a rich set of interactions between user‑mode providers and a kernel‑side filter driver, which gives it deep privilege and makes it a high‑value attack surface when parsing or reconciling user‑controlled inputs. Kernel filters that accept external inputs have historically produced local elevation primitives when parsing, validating, or synchronizing file metadata and reparse points.
CVE‑2025‑62462 is reported as a
buffer over‑read (CWE‑126) in the Windows Projected File System. In practical terms a buffer over‑read occurs when code reads beyond a memory buffer’s boundary; in privileged kernel code that can disclose kernel memory or, when combined with other primitives, be converted into control‑flow or memory‑corruption primitives that lead to SYSTEM escalation. The public registry entries and vulnerability trackers list the defect as a local attack requiring an attacker to interact with ProjFS surfaces on the host.
Why ProjFS vulnerabilities matter
- ProjFS operates in kernel context and acts on behalf of user‑mode providers. That combination of privilege and user‑facing input channels is a common pattern for serious elevation vulnerabilities.
- Mini‑filter drivers and file‑system brokering code are frequently abused as local escalation primitives because they can be induced to act on attacker‑controlled objects while running at SYSTEM privilege. Past disclosures for related components (Cloud Files / mini‑filter families and Brokering File System patterns) demonstrate this is not theoretical risk.
- In enterprise and cloud contexts the attack surface increases: hosts that automatically mount or process untrusted images, accept remote storage presentations, or run multi‑tenant agents that expose file provider interactions are highest priority for remediation. Historical incident patterns show local EoP bugs are commonly chained after a foothold to obtain full system control.
Technical analysis — what the public record says
The reported weakness and classification
Public vulnerability aggregators record CVE‑2025‑62462 as a
buffer over‑read within the Projected File System that can be used to elevate local privileges to SYSTEM. The CVSS v3.1 base score commonly assigned in feeds is
7.8 (High) with the vector indicating a local attack surface and low attack complexity once local access is available. The CVE is associated with CWE‑126.
Likely exploitation model
While the vendor advisory page is rendered behind a JavaScript UI (so low‑level exploit mechanics are not published directly in static HTML), the practical exploitation model for ProjFS buffer faults typically follows these steps:
- Attacker secures a local foothold (low‑privilege process, malicious user app, or code execution in a user session).
- The attacker crafts data or file operations that exercise ProjFS‑exposed paths (for example, specially formed placeholder metadata, reparse points, or DeviceIoControl interactions).
- The vulnerable ProjFS code performs an unchecked read beyond a buffer boundary, exposing kernel memory, crashing the kernel, or producing conditions that can be amplified into an arbitrary read/write or token theft primitive.
- The attacker turns the primitive into an elevation of privilege to the SYSTEM account and persists or moves laterally.
This attack path is consistent with other ProjFS and mini‑filter issues in recent years where incomplete validation, improper length checks, or race windows in brokering code were the root causes. Public analyses for related CVEs describe similar kernels of weakness: insufficient boundary checks, race conditions around path resolution, and mishandling of user‑supplied metadata.
Exploitability and attack complexity
- Preconditions: Local — an attacker must be able to run code on the device or otherwise influence file operations processed by ProjFS.
- Complexity: Low–Moderate — the underlying primitive (buffer over‑read) can be straightforward to trigger once a local process can interact with ProjFS; however, reliably converting an over‑read into an arbitrary write or code execution may require additional engineering (heap grooming, timing). Real‑world exploitation of ProjFS family bugs has been documented, which makes practical exploitation realistic in post‑compromise scenarios.
- Impact: High — successful exploitation yields SYSTEM privileges, which can lead to credential theft, persistence, and domain compromise in enterprise environments.
Note: Microsoft frequently omits low‑level exploit details from its public advisories to avoid enabling attackers; therefore, many technical specifics remain unverified in public records and defensive teams should treat the CVE as actionable regardless of public exploit proof.
Vendor status and patching posture
The CVE appears in December 2025 patch roundups and vulnerability feeds, and aggregator pages reference Microsoft’s Update Guide page for CVE‑2025‑62462 (which is dynamically rendered). That means Microsoft has recorded the issue in its Security Update Guide — operators should use the MSRC Update Guide and Microsoft Update Catalog to map the CVE to exact KB numbers and SKUs before deploying fixes. Public advisories commonly leave out exploit mechanics while confirming
patch availability for affected builds; always validate the CVE→KB→SKU mapping for each image before declaring remediation complete. Operational takeaway: prioritize identification of which Windows builds and SKUs in your estate include the vulnerable ProjFS implementation, then stage and apply the vendor KBs in a test ring before broad rollout.
Detection, hunting, and telemetry guidance
Because the vendor and third‑party advisories do not publish exploit PoCs, defenders must rely on behavior and telemetry to detect attempts or successful exploitation. Recommended detection signals:
- Kernel crash signatures and memory dumps that reference the ProjFS filter driver or Projected File System call stacks. Preserve full memory dumps for vendor triage when possible.
- Sudden process token changes or creation of services and scheduled tasks from previously non‑privileged accounts (indicative of a local elevation event).
- Unusual DeviceIoControl / IOCTL usage patterns against file system filter interfaces (audit if your EDR supports syscall/IO control monitoring).
- File system activity that mounts, projects, or materializes placeholder files in unusual locations, especially when performed by non‑privileged processes or automation tooling.
- Endpoint telemetry showing access to cloud placeholder metadata APIs combined with new persistence artifacts (service installs, driver load requests, autostart entries).
Hunt queries should combine kernel‑level indicators (BSOD/KMODE_EXCEPTION traces naming the ProjFS symbols) with host‑level anomalies (unexpected spawning of SYSTEM‑level processes). If exploitation is suspected, isolate the host, collect full memory and crash dumps, and engage incident response — ProjFS compromises can be leveraged to escalate and persist quickly.
Practical mitigation and hardening checklist
- Confirm applicability and inventory
- Inventory Windows builds, server SKUs, VDI, and developer machines where Projected File System or cloud file placeholder integrations (OneDrive, third‑party providers) are present.
- Prioritize systems that accept untrusted images, mount network shares, or run automation that interacts with projected files.
- Apply vendor patches (definitive fix)
- Use Microsoft Update Guide and the Update Catalog to obtain the exact KB for each affected SKU, then test and deploy in phased waves.
- Reboot machines as required by the security update to ensure kernel components are unloaded and the fix is active.
- Short‑term compensating controls (if patching is delayed)
- Restrict local code execution vectors: enforce application control (Windows Defender Application Control / WDAC) and limit who can install or run untrusted software.
- For hosts that mount images or ingest remote files automatically (CI runners, virtualization hosts, storage servers), disable automatic mounting of untrusted images or process them inside isolated sandboxes/VMs.
- Limit use of ProjFS providers or disable cloud placeholder features on high‑value servers until patched, where practical.
- Block or restrict access to management endpoints that can be abused to project files into privileged contexts.
- Post‑patch validation
- Verify KBs are present and that the patched driver versions are in place (check driver version strings and installation records).
- Reproduce normal workloads in a staging environment and validate no regressions occur.
- Monitoring and response
- Add EDR rules to alert on suspicious IOCTL activity, sudden token privileges escalations, and new service installs by non‑admin accounts.
- Preserve forensic artifacts and logs from any host that shows crash dumps or telemetry likely tied to ProjFS operations.
Risk analysis — who should worry most?
- Highest priority: Virtualization hosts, cloud/tenant hosts, CI/CD runners, and storage servers that accept untrusted images or mount external disk images. These environments magnify local vulnerabilities because a single malicious image or tenant can affect a shared host.
- Medium priority: Enterprise endpoints with cloud file integrations where users frequently access projected placeholders (OneDrive/Files On‑Demand) and where attacker code could be executed locally through social engineering or malicious installers.
- Lower priority (but not negligible): locked‑down single‑user desktops with limited local access controls and no third‑party placeholder providers; still, apply routine patching.
Exploit likelihood is elevated in post‑compromise scenarios: once attackers have a low‑privilege foothold they often weaponize local EoP primitives to gain SYSTEM, making timely patching and least‑privilege enforcement essential.
What is confirmed vs. what remains unverified
Confirmed facts (publicly recorded in multiple vulnerability feeds):
- CVE‑2025‑62462 exists and is associated with the Windows Projected File System.
- The weakness is described as a buffer over‑read and is classified under CWE‑126.
- Public feeds list the impact as Elevation of Privilege with a CVSS v3.1 base around 7.8.
Caveats and unverifiable details:
- The exact code path, the specific ProjFS symbols or function names affected, and any low‑level exploit mechanics are not published in static vendor pages (MSRC uses a dynamic UI and vendors avoid publishing exploit details). Until a vendor KB or trusted researcher publishes a technical write‑up, the precise exploitation technique (exact IOCTLs, buffer sizes, or race windows) is unverified and must be treated as such. Defensive guidance should therefore focus on patching, limiting local attack vectors, and monitoring.
Real‑world impact scenarios
- Post‑compromise escalation: an attacker initially compromises a standard‑user process via phishing or malicious installer. They then interact with ProjFS to trigger CVE‑2025‑62462, elevate to SYSTEM, and deploy persistence mechanisms or exfiltrate credentials.
- Multi‑tenant host compromise: a malicious tenant supplies crafted projected content or an image that is processed by the host; the host’s ProjFS code is triggered and the attacker achieves host‑level control, affecting all tenants.
- Developer workstation takeover: a developer machine with cloud placeholder sync and elevated privileges used for build signing can be escalated and abused to tamper with signing artifacts or push malicious builds into CI.
All of these are realistic given historical weaponization of ProjFS‑family and mini‑filter vulnerabilities in Windows.
Recommended timeline for defenders (practical runbook)
- Immediate (0–24 hours)
- Inventory systems with ProjFS or cloud placeholder features enabled.
- Identify and isolate any hosts that automatically process third‑party images or accept remote projected content.
- Short term (24–72 hours)
- Map CVE‑2025‑62462 → KB for your SKUs via Microsoft Update Guide and the Update Catalog; test the vendor patch in a pilot ring.
- If you cannot patch immediately, apply compensating controls: disable placeholder projection on critical servers, restrict who can mount or project files, and sandbox image processing.
- Medium term (3–14 days)
- Deploy patches broadly according to change control windows.
- Add detection rules and hunt for past indicators (crash dumps, abnormal IOCTLs, token changes).
- Validate that patched systems show no regression in normal file provider functionality.
- Post‑deployment (2–4 weeks)
- Review incident logs for the time window prior to patching for suspicious activity.
- Update playbooks and run tabletop exercises that include local escalation scenarios used in ransomware or post‑compromise chains.
Final assessment: strengths and risks
Strengths in the public record
- The vulnerability is tracked and cataloged in mainstream vulnerability feeds with a clear classification (buffer over‑read, CWE‑126) and CVSS scoring, which facilitates prioritization.
- Microsoft has recorded the CVE in its Update Guide (the advisory is available via the MSRC portal), so authoritative KB mappings should be forthcoming or already published behind the vendor UI. Operators can therefore obtain vendor fixes rather than relying solely on third‑party mitigations.
Risks and operational caveats
- The vendor’s omission of low‑level exploit details is standard but leaves defenders dependent on behavior‑based detection and timely KB mapping; attackers may still reverse‑engineer the patch diff to produce weaponized code if defenders delay.
- ProjFS issues are attractive to attackers because they provide a reliable, privileged bridge between userland inputs and kernel privilege; in practice, this raises the stakes for any host that exposes ProjFS surfaces, especially in multi‑tenant, virtualized, or automated image‑processing environments.
Cautionary note: treat any public claim about a PoC or confirmed in‑the‑wild exploitation conservatively until multiple, authoritative telemetry sources corroborate it — absence of a public PoC does not imply low urgency.
Quick checklist for systems administrators (one‑page)
- Inventory: find hosts with ProjFS / cloud placeholder integrations.
- Map: use Microsoft Update Guide to map CVE‑2025‑62462 to KB numbers for each Windows build.
- Patch: test then deploy vendor KBs; reboot as required.
- Mitigate: disable placeholder projection or auto‑mounting on critical hosts until patched.
- Hunt: search for kernel crash dumps referencing ProjFS, suspicious IOCTL activity, token escalations.
- Harden: enforce WDAC / least privilege and restrict local code execution for non‑admin users.
- Preserve: if compromise suspected, isolate host and collect full memory/crash dumps for IR.
CVE‑2025‑62462 is a timely reminder that kernel‑side file‑system brokers and mini‑filter components remain prime escalation targets. The public record shows the issue is real, serious, and actionable; defenders should treat it as a priority patching task, validate the CVE→KB mappings for their specific SKUs, and apply compensating controls in high‑risk environments until updates are confirmed and rolled out.
Source: MSRC
Security Update Guide - Microsoft Security Response Center