Understanding CVE-2025-54915: Local Privilege Escalation in Windows Defender Firewall Service

Microsoft’s Security Response Center has cataloged CVE-2025-54915 as an elevation-of-privilege vulnerability in the Windows Defender Firewall Service described as “Access of resource using incompatible type (‘type confusion’),” and the vendor advises that an authorized local attacker could leverage this bug to elevate privileges on an affected host. (msrc.microsoft.com)

Background​

Type‑confusion vulnerabilities occur when code treats an object or memory region as one data type while it actually represents another, producing incorrect offsets, corrupted vtables or function pointers, and often enabling memory-corruption primitives. In privileged Windows services these primitives can be converted into token steals or control‑flow hijacks that yield SYSTEM-level access. The Windows Defender Firewall Service (service name: MpsSvc) is a core, always‑present component of modern Windows builds; it participates in the Windows Filtering Platform and runs under a service account (NT SERVICE\MpsSvc / LocalService context in many builds), which makes any memory‑safety flaw in its code a potentially powerful local escalation vector. (learn.microsoft.com)
Microsoft’s published advisory for CVE-2025-54915 is concise in public-facing wording (to limit weaponization) but confirms three operational facts that matter to administrators:

• The flaw is a type confusion error in the Windows Defender Firewall Service. (msrc.microsoft.com)
• The attack vector is local and authorized — an attacker must already be able to run code or interact on the target host as a valid user. (msrc.microsoft.com)
• The impact is privilege escalation — the adversary can raise privileges on the machine when exploitation succeeds. (msrc.microsoft.com)

These facts define the practical risk model: CVE‑2025‑54915 is not a remote unauthenticated RCE; it is a local elevation-of-privilege that is most dangerous when chained with an initial foothold (malicious macro, browser compromise, credential theft, or user‑session compromise).

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Why this matters: context and prevalence​

Windows firewall functionality is not an optional luxury in modern Windows deployments. The Windows Defender Firewall Service (MpsSvc) interfaces with the Windows Filtering Platform (WFP) and is relied upon by many subsystems and third‑party products; stopping the service is unsupported and often impossible on recent builds, which means the vulnerable component is present on a very large number of endpoints and servers. That wide presence increases the potential blast radius of a local EoP bug. (learn.microsoft.com)
Memory‑safety bugs in privileged Windows subsystems — Win32K, notification stacks, DWM, firewall/filtering subsystems, and device drivers — have been a recurrent source of local privilege escalation in recent years. Patch‑Tuesday cycles in 2024–2025 repeatedly included EoP fixes for notification, graphics, and firewall/driver components; industry analysis shows a persistent trend of type‑confusion and use‑after‑free vulnerabilities being weaponized soon after disclosure when they touch privileged services. Administrators should therefore treat a new type‑confusion EoP in the firewall service with high priority. (crowdstrike.com, blog.qualys.com)

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Technical overview: what “access of resource using incompatible type” implies​

The vulnerability class, explained​

At a high level, a type‑confusion flaw is triggered when the code expects a resource of Type A but receives or interprets it as Type B. In C/C++ implementations that use vtables, COM objects, or serialized object headers, such confusion can:

• cause the process to read or write at incorrect offsets;
• treat attacker‑controlled data as pointers (including function pointers) or vtable entries;
• cause out‑of‑bounds reads/writes that enable info leaks, pointer corruption, or arbitrary write primitives.

When this occurs inside a service executing with elevated privileges, the attacker may be able to convert memory corruption into a privilege escalation path (token replacement, impersonation, or loading a malicious module under a trusted context). These chains typically require additional primitives (heap grooming or info leaks), but they are well known in Windows exploit development.

Likely exploitation chain (responsible, high-level sketch)​

• Adversary obtains a local, low‑privilege process on the target (e.g., via phishing, malicious installer, or a sandbox escape).
• That process invokes an API or crafts input that exercises the vulnerable firewall code path.
• The service misinterprets the object/structure type and dereferences memory with the wrong layout, enabling controlled corruption.
• Using heap grooming and other primitives, the attacker converts the memory corruption into a token or context manipulation that the OS accepts as a legitimate elevation to SYSTEM or another privileged account.
• The attacker persists, disables protections, or moves laterally from the elevated context.

This is an abstracted exploitation model based on prior analyses of similar class defects; Microsoft’s advisory intentionally omits exploitable details to slow weaponization. Treat public PoCs or third‑party technical writeups with caution until they are validated.

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Affected systems and verification caveats​

Microsoft’s Security Update Guide entry is the authoritative source for which Windows builds and SKUs are affected and for the exact KB/security update identifiers. Because the Microsoft MSRC page is rendered dynamically and sometimes does not expose static text for automated scrapers, administrators must confirm impact and applicable KB numbers through:

• The MSRC Security Update Guide entry for CVE‑2025‑54915. (msrc.microsoft.com)
• The Microsoft Update Catalog or your enterprise patch management console (WSUS, SCCM, Microsoft Intune) where KB mapping is visible. (msrc.microsoft.com)

Until those KBs are consulted and mapped to your environment, treat platform impact estimates as provisional. Community trackers and vulnerability databases often replicate vendor lists quickly, but differences in CPEs, CVSS scores, or patch identifiers can occur; always reconcile against Microsoft’s published update metadata before automating enforcement or blocking updates.

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Immediate operational impact and prioritized response​

Why this should be prioritized​

• The vulnerable component is present by default on most Windows clients and servers, increasing exposure surface area. (learn.microsoft.com)
• Successful exploitation could yield SYSTEM or equivalent privileges on hosts, enabling persistence, lateral movement, and full compromise of workstation or server assets.
• Local EoP bugs are commonly chained with widely available initial access vectors (malicious documents, drive‑by exploits, credential compromise), making the window between disclosure and weaponization short in practice. (crowdstrike.com)

Immediate checklist (operational triage)​

• Identify affected hosts: query inventory for the Windows Defender Firewall Service (MpsSvc) presence and Windows builds that map to the MSRC advisory. Use your endpoint management tooling to export the installed build numbers and current cumulative update KBs. (msrc.microsoft.com)
• Patch rapidly but safely: test the Microsoft update that addresses CVE‑2025‑54915 in a representative lab and then deploy across your change windows via WSUS/SCCM/Intune. The vendor update is the canonical fix. (msrc.microsoft.com)
• Prioritize rollout: start with exposed and high‑value systems — domain controllers, admin workstations, RDP/VDI hosts, and servers with interactive user logons. Then expand to general endpoints.
• Apply least‑privilege controls: remove unnecessary local admin rights, require separate privileged accounts for admin tasks, and tighten application allow‑listing where feasible.
• Monitor during rollout: enable heightened telemetry and hunt for exploitation signals (see detection section).

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Detection and hunting guidance​

Type‑confusion exploitation often triggers noisy failures before a final privileged payload succeeds. Use these telemetry signals to detect exploitation attempts or post‑exploit activity:

• Service crashes and restart patterns: repeated crashes of the Windows Defender Firewall service (MpsSvc) or correlated svchost process instability. Watch Event Log service termination and crash events.
• Abnormal process behavior under non‑privileged sessions: processes spawning children that then perform privileged operations, create scheduled tasks running as SYSTEM, or alter HKLM registry hives.
• Suspicious module loads or memory corruption alerts from EDR: mismatched module images, runtime instrumentation warnings, or memory integrity checks failing.
• Indicators of privilege escalation: sudden creation of services, additions to the Local Administrators group, or unexpected modifications to the service binary path attributed to non‑admin users.

Practical EDR rules to consider:

• Alert on Event ID patterns tied to service crashes for MpsSvc and correlate with process creation logs.
• Watch for parent/child process lineage anomalies where a user‑level process spawns a process that later requests token adjustments.

If you lack mature EDR capabilities, increase collection of process creation, module loads, and registry write events to a centralized SIEM for hunting during patch rollout windows.

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Temporary mitigations and hardening (when patching is delayed)​

The vendor fix is the definitive mitigation. If you cannot immediately deploy the patch across your estate, consider layered mitigations:

• Reduce local interactive exposure: restrict RDP and interactive access to management subnets or VPNs, and remove or rotate any shared local accounts.
• Enforce least privilege and application control: restrict which binaries users can run and implement WDAC/SmartScreen policies where feasible.
• Isolate high‑risk hosts: disconnect or segment machines that run untrusted workloads until patched.

Note: disabling the Windows Defender Firewall Service is unsupported in modern Windows and can break dependent features; it’s not a recommended mitigation. Instead, use network segmentation and access restriction to reduce the chance of an attacker obtaining the required local foothold. (learn.microsoft.com)

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Risk assessment: strengths, likely attack scenarios, and caveats​

Notable strengths / reasons to be reassured​

• Microsoft has published an advisory and (per MSRC) released updates that address the issue; administrators have a vendor-supplied remediation path. This reduces long‑term operational uncertainty. (msrc.microsoft.com)
• The attack vector is local and authorized; organizations that enforce strict least‑privilege practices (no local admin for users, limited interactive access) reduce immediate exploitation likelihood. (msrc.microsoft.com)

Significant risks and why they matter​

• High impact if exploited — the vulnerable service is privileged and ubiquitous; a successful exploit can produce a full system compromise.
• Chaining risk — the bug is particularly valuable when combined with a remote initial access vector (malicious attachments, browser RCEs, or social‑engineering attacks). Past incidents show local EoP bugs are frequently incorporated into multi‑stage compromises. (crowdstrike.com)
• Widespread presence — because MpsSvc is present by default, large fleets that delay patching increase enterprise exposure. (learn.microsoft.com)

Caveats and unverifiable items​

• At the time of publication there is no widely‑trusted, public proof‑of‑concept code for CVE‑2025‑54915 that has been validated by multiple independent researchers. Administrators should treat unvetted PoCs with extreme caution and verify provenance before test‑running them. If a PoC appears in the wild, the exploitation window often shrinks dramatically.

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How this fits into the broader Patch‑Tuesday and Windows security landscape​

Microsoft’s monthly updates continue to address numerous local EoP issues across Windows subsystems (graphics, notification stacks, firewall/filtering, and various drivers). Enterprise security teams should consider CVE‑2025‑54915 part of an ongoing trend: memory‑safety defects in privileged components remain the most common avenue for local privilege escalations and sandbox escapes. Past vendor advisories and industry writeups show that EoP bugs are often folded into malware toolchains quickly after disclosure, underscoring the need for rapid patching and layered defense. (blog.qualys.com, crowdstrike.com)
Security vendors and threat intelligence teams often publish corresponding rules and protections in parallel with Microsoft’s updates (for example, MAPP‑program partners and AV/EDR vendors will typically deploy heuristic or signature protections once a patch is public). Monitoring vendor advisories (and applying vendor‑supplied protections) can reduce exposure during the initial patching window. (tenable.com)

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Practical deployment checklist (step‑by‑step)​

• Fetch MSRC advisory and map affected KB(s) to each OS build in your inventory. Confirm KB names in the Microsoft Update Catalog for the exact build numbers your environment runs. (msrc.microsoft.com)
• Test the update on representative machines (user workstation, admin workstation, RDP host, domain‑joined server). Validate business apps and networking functions.
• Schedule staged rollouts: patch critical servers and admin workstations first, then end-user machines. Use rings to detect unforeseen regression signals.
• Ensure EDR/antivirus signatures and heuristics are up to date and tuned to capture service crash anomalies or privilege escalation patterns.
• After rollout, run hunts for: recent service crash events, unexpected scheduled tasks created by non-admin users, new local admin additions, and unexplained service binary path changes.

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Closing analysis and recommendation​

CVE‑2025‑54915 is a high‑priority, local elevation‑of‑privilege vulnerability that targets a fundamental and widely deployed Windows component. The vulnerability’s type‑confusion classification aligns with a class of bugs that historically have been used in privilege‑escalation toolchains. Because the Windows Defender Firewall Service operates in privileged contexts and is effectively ubiquitous on Windows endpoints and servers, organizations should treat this advisory as urgent.
Action priorities:

• Immediately identify and patch affected systems using Microsoft’s updates (MSRC and the Update Catalog are the authoritative sources for KB mapping). (msrc.microsoft.com)
• Prioritize critical infrastructure and admin endpoints for early updates, and strengthen host‑level controls (least privilege, WDAC, EDR).
• Enhance telemetry and hunting for the detection signals outlined above while the patch window is open.

Finally, remain vigilant for follow‑on public disclosures or PoCs; these can shorten the time to exploitation materially. Treat any third‑party exploit code as potentially weaponized until independently validated, and verify all remediation steps against Microsoft’s official advisory and your patch management console before automated enforcement. (msrc.microsoft.com)

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(Technical verification note: the description and advisory for CVE‑2025‑54915 come from Microsoft’s Security Update Guide entry for that CVE. Additional technical context, exploitation patterns, and detection/mitigation recommendations in this article synthesize vendor guidance with industry practice and post‑disclosure analysis of type‑confusion and local EoP vulnerabilities. Where Microsoft’s public advisory is brief or dynamically rendered, administrators should consult the MSRC entry and the Microsoft Update Catalog to obtain the exact KB identifiers before patching automation.) (msrc.microsoft.com)

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Source: MSRC Security Update Guide - Microsoft Security Response Center