CVE-2025-54094: Type-Confusion in Windows Defender Firewall Service Enables Local EoP

Microsoft’s security advisory for CVE-2025-54094 identifies a type‑confusion flaw in the Windows Defender Firewall Service that can be triggered by an authorized local actor to perform a local Elevation of Privilege (EoP) — in short, an attacker with the ability to run code as a non‑privileged user can potentially escalate to SYSTEM by abusing how the Firewall service accesses resources. (msrc.microsoft.com)

Background / Overview​

The newly disclosed CVE‑2025‑54094 is classed by Microsoft as an access of resource using incompatible type (‘type confusion’) vulnerability in the Windows Defender Firewall Service. That description signals a memory‑safety issue where the component treats an object or buffer as the wrong data type, creating opportunities to corrupt memory, redirect control flow, or overwrite security‑critical fields — all of which are common building blocks for privilege escalation exploits. (msrc.microsoft.com)
Type‑confusion bugs are one of a family of memory‑safety problems (alongside use‑after‑free and heap overflows) that have repeatedly produced local EoP issues across Windows system services in recent months. Public analyses show a steady pattern: privileged services exposed to user‑mode inputs often become high‑value targets because a memory corruption primitive in a service running as SYSTEM yields immediate and powerful escalation potential. (nvd.nist.gov, zeropath.com)
This advisory is important for any organization that allows local user accounts to run arbitrary code (standard user desktops, developer machines, labs, or servers where local logins are allowed). Because the attack vector is local and authorized, the immediate remote worm‑style risk is low; the operational risk comes from chaining this EoP with initial access methods (phishing, malicious installers, unvetted software) or insider threats.

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What “type confusion” means here​

The technical root: incompatible type access​

A type‑confusion vulnerability happens when the program assumes a pointer or resource references one type of object while it actually holds another. That assumption permits the code to:

• Treat untrusted data as function pointers, vtables, or object headers;
• Read or write fields at offsets that were never intended for the real underlying resource;
• Jump to attacker‑controlled function addresses by overwriting dispatch pointers.

When the vulnerable code runs in a privileged context (such as the Windows Defender Firewall Service, which has elevated privileges), the consequences can escalate from crashes to privilege elevation. This is a well‑understood risk model in modern OS security analyses.

Why a seemingly small mismatch becomes catastrophic​

In usermode services, simple mis‑typed memory dereferences can be converted into powerful primitives by attackers who can:

• Control the memory layout (heap/stack) to place crafted data at predictable locations.
• Coerce the service to dereference those locations as the wrong type.
• Overwrite function pointers, vtables, or callback targets executed later by the service.

Experienced exploit developers can often convert such primitives into token manipulation, impersonation, or direct code execution in the service context — enabling SYSTEM‑level operations. Public write‑ups on similar Windows type‑confusion CVEs document precisely this progression. (zeropath.com)

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Affected components, scope, and severity​

Microsoft’s entry for CVE‑2025‑54094 identifies the Windows Defender Firewall Service as the vulnerable component. Administrators should assume the vulnerability affects supported Windows client and server SKUs until product/KB mappings are checked against vendor guidance. Because the Firewall service runs with elevated privileges on most installations, a local EoP in this component is high‑impact if exploited. (msrc.microsoft.com)
Important operational notes:

• The vulnerability requires local, authorized access — remote exploitation without any local foothold is not the canonical vector.
• The exploitability classification for type‑confusion bugs varies: some require complex memory grooming and timing, others can be simpler. Administrators should treat the risk as high for endpoints where local accounts are common.

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Exploitation scenarios and attack chains​

Typical chains for local EoP vulnerabilities​

• Initial access: A phishing email, malicious macro, or compromised installer gets code running as a standard user.
• Local EoP: The attacker triggers the type‑confusion vulnerability in the Firewall service to gain SYSTEM privileges.
• Persistence and lateral movement: With SYSTEM, the attacker installs backdoors, harvests credentials, moves laterally across the network or deploys ransomware.

Because adversaries increasingly favor multi‑stage attacks, a local EoP like CVE‑2025‑54094 is valuable in any chain where an attacker already has a foothold. Public analyses emphasize that even when the initial vector is limited, combining it with a high‑impact EoP produces a disproportionate threat.

Who is most at risk?​

• Developer machines and test workstations where users run unvetted code.
• Corporate desktops where users have standard accounts but run local software installations.
• Shared lab or kiosk systems where local accounts can be created or abused.
• Older or out‑of‑support Windows installations that may not receive patches.

Temporary mitigations like disabling the vulnerable service are possible but can disrupt functionality; patching is the preferred fix path.

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What Microsoft has published — and what remains unclear​

Microsoft’s Security Response Center (MSRC) lists the CVE and classifies the issue as a type‑confusion EoP in the Windows Defender Firewall Service. The MSRC entry provides an authoritative acknowledgement that a fix has been issued or will be issued via Microsoft’s update channels; however, the MSRC pages are dynamically rendered and can be terse by design — they often omit deep technical details to reduce weaponization risk. (msrc.microsoft.com)
Cross‑checks with public vulnerability trackers for similar type‑confusion CVEs show a consistent pattern: vendor advisories confirm the class of bug, while third‑party aggregators add CPE/CVSS metadata after vendor updates propagate. Administrators should verify KB numbers and affected builds directly in the MSRC update guide and Microsoft Update Catalog rather than rely solely on aggregator snapshots. (nvd.nist.gov, app.opencve.io)
Caveat: At the time this article was prepared, some third‑party databases lag in indexing specific CVE entries (a recurring, documented issue in public CVE pipelines). If you need automated CVE‑based blocking or policy enforcement, validate the exact KB and CPEs from Microsoft before applying rigid rules.

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Detection signals and forensic guidance​

Type‑confusion exploitation often produces noisy precursors. Useful host‑level signals to monitor include:

• Unexpected crashes or restart events for the Windows Defender Firewall Service (Service Control Manager events).
• svchost.exe instances hosting Firewall service threads exhibiting anomalous behavior, unexpected child processes, or unusual module loads.
• Endpoint Detection & Response (EDR) telemetry showing token manipulation, impersonation calls, or processes attempting to create scheduled tasks in SYSTEM context.
• Registry writes under HKLM with recent creation times coinciding with suspicious process activity.

EDR products and SIEM rules should be tuned to look for abnormal behavior in service host processes and for local processes attempting to access privileged service interfaces. Early detection is valuable because many exploit attempts will cause instability before a final payload succeeds.

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Immediate mitigation and patch guidance​

Priority actions (ordered)​

• Patch immediately where possible: Apply Microsoft’s cumulative and security updates that include the fix for CVE‑2025‑54094 via Windows Update, WSUS, SCCM, or Intune. MSRC and the Microsoft Update Catalog contain authoritative KB/build mappings. (msrc.microsoft.com, app.opencve.io)
• Inventory and prioritize by exposure: Identify machines where local code execution is likely (developer laptops, test servers, machines allowing local account creation) and accelerate patch deployment to those groups. Inventorying by service name (Windows Defender Firewall service / mpssvc) is a fast way to find affected systems.
• Temporary mitigation (if patching cannot be immediate): Consider temporarily disabling the Windows Defender Firewall Service on segmented or high‑risk hosts only after validating business impact. Disabling mpssvc reduces the attack surface but may impair network protection and application connectivity; do not roll this out broadly without testing. Example: set the service Start type to disabled via services.msc or registry, and re‑enable after patching.
• Harden endpoints: Enforce least privilege, apply application control (Windows Defender Application Control, AppLocker), and restrict local admin rights. These measures reduce the chance that an attacker can run the arbitrary local code required to exploit CVE‑2025‑54094.

How to verify remediation​

• Confirm the KB/build mapping for your OS from MSRC or Microsoft Update Catalog.
• Use centralized update reporting (WSUS/Intune/SCCM) to prove patch coverage.
• Monitor event logs for disappearance of the crash/restart signals tied to the vulnerable service.

If automation depends on CVE IDs and CPEs, cross‑validate those values against Microsoft’s published advisory rather than relying only on third‑party databases, which may lag. (msrc.microsoft.com, app.opencve.io)

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Longer‑term hardening and recommended controls​

• Enforce principle of least privilege across the estate and ensure standard users cannot install or execute unapproved binaries.
• Deploy application allow‑listing where feasible, particularly on high‑value endpoints and servers.
• Harden logging and EDR telemetry to capture service crashes, token impersonations, and unusual process-creation chains.
• Maintain robust patch cycles (test → staged rollout → full deployment) and include emergency choreography for high‑impact local EoP patches.

These controls meaningfully reduce both the probability that an attacker will get the initial foothold and the damage if an EoP is attempted.

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How exploit complexity affects your risk calculus​

Type‑confusion bugs range from trivially exploitable to extremely intricate. Practical exploitability depends on:

• Whether an attacker can reliably control allocation and object lifetimes (heap grooming).
• Timing windows and race conditions that may be required to turn a type‑confusion into a functional code path.
• Availability of existing primitives (info leaks, other memory mismanagement) that simplify exploitation.

Operationally, assume moderate to high risk until proven otherwise: attackers routinely find creative ways to chain multiple primitives, and many publicly disclosed Windows service vulnerabilities have progressed from conceptual reports to weaponized exploits in short order. Treat CVE‑2025‑54094 as a high‑priority fix candidate. (zeropath.com)

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Strengths, limitations, and where to be cautious​

Strengths / positive signals​

• Vendor action exists: Microsoft has published the advisory and the remediation path is through standard update channels. That makes fast remediation operationally possible. (msrc.microsoft.com)
• Vector is local: Without a local foothold, the flaw cannot be trivially weaponized across the network, reducing immediate worm potential.

Limitations / risks​

• High impact if exploited: Because the firewall service runs with elevated privileges on most machines, a successful exploit enables SYSTEM‑level control.
• Widespread presence: The Windows Defender Firewall Service is installed and active by default in the majority of supported Windows installations, increasing the blast radius for unpatched fleets.
• Third‑party databases may lag: CVE indexing, CPE lists, and CVSS scoring sometimes appear later in NVD/aggregators; rely on MSRC and Microsoft Update Catalog for authoritative patching decisions. (app.opencve.io)

Unverifiable or uncertain items (flagged)​

• If specifics of exploit technique, PoC availability, or exploit code circulation are not documented publicly, treat claims about exploitability as provisional until independent researchers publish verified PoCs or Microsoft provides more detail. Avoid assuming a public PoC exists unless explicitly confirmed.

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Recommended checklist for administrators (quick actions)​

• Check MSRC entry for CVE‑2025‑54094 and note the KB/build mapping for your OS family. (msrc.microsoft.com)
• Stage patching: deploy to a pilot group, validate, then roll out to wider user base.
• If immediate patching is impossible, evaluate temporary service disablement on segmented hosts after testing for functional impact.
• Harden endpoints: remove unnecessary local admin privileges, apply application control, and ensure EDR agents are reporting telemetry.
• Hunt for indicators: monitor Service Control Manager events, unusual svchost behavior, token impersonation activity, and new SYSTEM‑context scheduled tasks.

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Conclusion — realistic, urgent, and actionable​

CVE‑2025‑54094 is a classic example of how memory‑safety bugs in privileged services remain a critical Windows security surface. The vulnerability’s classification — type confusion in the Windows Defender Firewall Service — plus the privileged context of that service, elevates the issue to high operational importance. Microsoft’s advisory confirms the problem and provides the remediation path; administrators should treat this as a high‑priority patching event and follow the mitigation checklist above. (msrc.microsoft.com)
Finally, while this advisory is specifically about the Firewall service, it also underscores a broader trend: privileged, widely deployed services that interact with user‑mode inputs remain a favored vector for EoP exploits. Strong patching discipline, least‑privilege policies, and layered endpoint defenses are the most reliable defenses against such bugs — both now and as future CVEs are disclosed.

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Source: MSRC Security Update Guide - Microsoft Security Response Center