CVE-2025-53718: Windows AFD.sys UAF Privilege Escalation — Patch, Detect, Harden

Microsoft’s Security Update Guide entry for CVE-2025-53718 describes a use‑after‑free (UAF) flaw in the Windows Ancillary Function Driver for WinSock (AFD.sys) that can be triggered by a locally authorized user to obtain elevated privileges on affected Windows hosts — a kernel‑level elevation‑of‑privilege (EoP) issue that system owners must treat as high priority for remediation and detection.

Background / Overview​

The Windows Ancillary Function Driver for WinSock (AFD.sys) is a kernel‑mode driver that implements low‑level socket and Winsock functionality used by virtually every networked application in Windows. Because AFD runs in kernel mode and is reachable from numerous user‑mode APIs and IOCTL/device control paths, memory-safety bugs there — including use‑after‑free, null dereference, untrusted pointer dereference, heap overflow, and race conditions — have repeatedly produced full SYSTEM compromise or other high‑impact outcomes when chained with local access. Multiple AFD-related CVEs appeared in 2024–2025, establishing a pattern and raising the operational urgency for new AFD advisories. (nvd.nist.gov, zeropath.com)
The vendor entry that the user provided summarizes CVE‑2025‑53718 as a use‑after‑free in AFD.sys that “allows an authorized attacker to elevate privileges locally.” The advisory makes two crucial operational points: the attack vector is local (an attacker must be able to run code or a process on the target) and the underlying fault is a kernel memory‑safety problem that can, in practice, be converted into a powerful kernel primitive by skilled attackers.

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Why AFD.sys vulnerabilities are high‑impact​

• AFD.sys executes in kernel context, so any corruption or hijacked control flow there runs with the highest privileges on the host.
• AFD is reachable via common user‑mode APIs (Winsock), so non‑privileged processes can potentially exercise vulnerable code paths.
• Kernel use‑after‑free and race conditions can be turned into write‑what‑where or function‑pointer overwrite primitives, enabling token replacement, SYSTEM code execution, kernel rootkits, or persistent implants. (zeropath.com, bleepingcomputer.com)
• Historical precedence: several AFD bugs in 2024–2025 were quickly turned into proof‑of‑concepts and, in at least one widely reported instance, exploited in targeted attacks. That history increases the probability that new AFD advisories will be weaponized rapidly. (bleepingcomputer.com, global.ptsecurity.com)

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Technical summary: what a use‑after‑free in AFD typically enables​

What a use‑after‑free is (concise)​

A use‑after‑free (UAF) occurs when kernel code continues to use a pointer after the memory it refers to has been freed. If an attacker can reallocate that freed memory with attacker‑controlled contents and then cause the driver to dereference the stale pointer, the kernel will operate on attacker‑controlled data — a typical path toward arbitrary kernel memory write or control‑flow hijack.

Typical exploitation pipeline seen in AFD advisories​

• Attacker obtains local code execution (low‑privileged process).
• Attacker triggers the vulnerable AFD path that frees or invalidates an internal object while a stale reference remains.
• Attacker forces an immediate reallocation of the freed pool with attacker‑controlled data (heap spraying, controlled kernel allocations).
• Attacker causes the driver to dereference the dangling pointer, using the attacker data to overwrite kernel pointers or structures.
• The primitive is leveraged to alter a process token or function pointer, producing SYSTEM‑level execution.

Exploit complexity and reliability​

• These faults are often timing‑dependent (races) or require careful allocation sequencing (UAFs). That adds complexity, but skilled attackers and automated exploit frameworks can reliably “win” races or automate spraying/reallocation to build robust primitives. Historically, once a reliable trigger is identified for AFD, working exploits follow quickly.

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Affected systems and patching posture​

Microsoft’s security guidance for AFD advisories typically covers a broad range of supported Windows client and server SKUs; the fix is delivered as a driver update (afd.sys updated) via cumulative updates or out‑of‑band patches depending on urgency. Administrators must map the MSRC advisory to the KB(s) that correspond to their specific OS builds before deploying. Automated patch channels (Windows Update, WSUS, Microsoft Endpoint Manager) will reflect the published KB once the vendor release is fully propagated. (msrc.microsoft.com, rapid7.com)
Operationally:

• Prioritize terminal servers, RDS/VDI hosts, developer workstations, and systems where non‑admin users can run code.
• Verify afd.sys file versions and timestamps across the estate; patched systems will show updated afd.sys metadata. Use EDR or inventory tooling to find mismatches.

Caveat on the CVE index: some MSRC entries are published before public indexing is complete at third‑party aggregators (NVD, vendor DBs). If an exact CVE mapping is required by compliance processes, confirm the MSRC advisory text and KB numbers against your patch‑management systems; do not rely on a single third‑party index.

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Detection, telemetry, and hunting guidance​

Because exploitation often leaves limited, noisy traces at the kernel level, a layered detection strategy is required.

• AFD.sys inventory
• Build an inventory of afd.sys file versions and timestamps across all endpoints; treat unpatched versions as high priority. File metadata changes reliably after a patch, so this is a fast scope check.
• Monitor IOCTL / DeviceIoControl patterns
• Flag non‑privileged processes that call DeviceIoControl against AFD device interfaces at high rates or in tight loops. Exploit code frequently loops to win timing windows.
• High‑frequency Winsock activity from low‑privileged processes
• Repeated low‑level Winsock or socket control operations originating from user processes can indicate attempts to trigger AFD race windows. Correlate with process creation, command shell spawning, or memory‑dumping attempts.
• Kernel integrity telemetry
• Use kernel sensors (HVCI, Driver Guard, EDR kernel detectors) to detect unexpected kernel writes, driver object modifications, or unexpected allocations tied to afd.sys. These signals are high‑value but can be noisy — tune thresholds.
• Post‑escalation behavior
• Treat SYSTEM‑level behavior from previously unprivileged accounts as a high‑confidence compromise indicator. Look for credential dumping attempts, new driver loads, or lateral‑movement patterns after any suspicious IOCTL/Winsock activity.

Example EDR detection rule (template)

• “Alert when a non‑system process calls DeviceIoControl against afd.* device names more than N times/minute and spawns cmd.exe or powershell shortly afterward.”

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Immediate, practical remediation checklist (24–72 hours)​

• Confirm the vendor advisory and applicable KB numbers for your OS builds via Microsoft’s Security Update Guide entry for CVE‑2025‑53718 and your enterprise patch tooling. Apply patches to test and production rings per change control.
• Prioritize remediation for multi‑user systems: terminal servers, developer workstations, admin consoles, and frequently‑shared endpoints.
• Inventory afd.sys file versions across the estate; create automated queries to flag outliers.
• Implement or tune EDR hunting rules to detect high‑rate DeviceIoControl/IOCTL calls and unusual Winsock operations from non‑admin processes.
• Enforce least‑privilege and application control where possible (WDAC/AppLocker) to reduce the ability of non‑admins to run exploit code.
• If compromise is suspected, isolate and collect forensic evidence (memory, kernel traces) and plan for reimaging if kernel modifications are detected. Kernel‑level compromises often require full rebuilds.

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Operational impact and prioritization​

• High priority: multi‑user remote access hosts (RDS, Citrix, VDI), domain controllers, management jump boxes.
• Medium priority: developer workstations and build servers where untrusted code may run.
• Lower priority: tightly controlled single‑user desktops, provided that application control and least‑privilege are enforced.

When past AFD issues were publicly exploited, defenders prioritized externally accessible or multi‑user systems due to the higher blast radius; treat CVE‑2025‑53718 with the same risk model until organizational telemetry says otherwise.

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Strengths in Microsoft’s response — and remaining concerns​

Notable strengths:

• Microsoft publishes security advisories through the Security Update Guide and distributes fixes via well‑understood channels (Windows Update, WSUS, MECM), enabling rapid enterprise roll‑out.
• Vendor and independent research communities typically produce rapid technical analysis and detection guidance after patch release, which helps defenders tune telemetry and response.

Potential risks and weaknesses:

• Kernel vulnerabilities are inherently high‑risk; a single synchronization or validation error can result in SYSTEM compromise.
• AFD has been the subject of multiple high‑severity CVEs in 2024–2025, suggesting a recurring engineering and testing gap in the concurrency and pointer‑validation logic used by the driver.
• Public indexing and PoC release timing are variable: some MSRC advisories appear before aggregators (NVD, vendor DBs) or before public PoCs show up. That can create confusion for compliance programs tied to specific CVE IDs or KB numbers.

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Verification, uncertainty, and cautionary notes​

• Confirmed vendor statement: The MSRC Security Update Guide entry the user supplied describes CVE‑2025‑53718 as a use‑after‑free in AFD.sys that allows local privilege elevation. Use the MSRC advisory text and the KB(s) it references as your authoritative source for affected builds and remediation.
• Cross‑verification: Independent trackers and vendors have documented multiple AFD UAF/heap/race issues in 2025 (examples: CVE‑2025‑32709, CVE‑2025‑21418, CVE‑2025‑49661), which corroborate the technical pattern and exploitation profile described by Microsoft. Those independent writeups confirm both the high risk posed by AFD bugs and the common exploitation pipeline (UAF → controlled reallocation → kernel primitive → token or pointer overwrite). Use those as technical context.
• Unverified or variable items:
• At the time of verification, some third‑party vulnerability collections may not yet have indexed CVE‑2025‑53718 under that specific numeric label. Organizations that require a CVE–KB mapping for patch approval should confirm the exact KB numbers referenced in the MSRC advisory before approving/rolling updates. Treat any single‑source claim about CVSS scores, KEV/active‑exploitation status, or exploit availability as provisional until confirmed by multiple vendor/government feeds.
• Public proof‑of‑concept code for a specific CVE number may be absent from open sources even while private exploit code exists. Absence of public PoC is not proof of safety; historical AFD CVEs have been weaponized quickly after disclosure. (zeropath.com, bleepingcomputer.com)

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Longer‑term hardening and mitigation strategies​

• Enforce least‑privilege and reduce the number of users who can run arbitrary code on critical hosts.
• Deploy application control (WDAC / AppLocker) to restrict the set of binaries non‑admin users can execute.
• Maintain kernel‑protection features where supported (HVCI / Memory Integrity) to raise the bar for kernel exploitation.
• Keep endpoint telemetry and EDR sensors updated; ensure kernel sensors are active and that alerts for driver anomalies are routed to incident response.
• Incorporate kernel fuzzing and targeted code audits into the secure development lifecycle for critical drivers — the pattern of recurring AFD bugs suggests targeted engineering investment here could reduce future incidents.

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Conclusion​

CVE‑2025‑53718 — as published by Microsoft — is a kernel use‑after‑free in the Windows Ancillary Function Driver for WinSock (AFD.sys) that can be exploited by a locally authorized attacker to escalate privileges to SYSTEM. The technical class and entry points are consistent with prior AFD advisories in 2024–2025, which have repeatedly proven to be high‑impact and rapidly weaponized. Administrators should treat this advisory as urgent: confirm the exact KB(s) that apply to your Windows builds, prioritize patching multi‑user and remote‑access systems, implement the detection rules described above, and harden local privilege and application control policies while you deploy the vendor fixes. Rely on the MSRC advisory and your patch‑management system for the authoritative KB mapping, and treat single‑source claims about exploitation status or CVSS scoring with caution until multiple reputable trackers corroborate them. (msrc.microsoft.com, rapid7.com, zeropath.com)

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Source: MSRC Security Update Guide - Microsoft Security Response Center