On April 10, 2025, a new local privilege escalation vulnerability was uncovered in Microsoft Windows' core network subsystem, specifically in the Ancillary Function Driver for WinSock (AFD.sys). Tracked as CVE-2025-32709, this vulnerability centers around a *use-after-free* (UAF) condition. Unlike remote code execution flaws, CVE-2025-32709 can only be exploited locally—but given its wide impact and ease of exploitation, it’s important for Windows users and admins to understand the details.

This exclusive article walks you through the vulnerability, how attackers can exploit it, includes code snippets, and links to official references.

What Is AFD.sys?

AFD.sys is the Ancillary Function Driver (AFD) for WinSock, an essential kernel-mode system driver that helps Windows manage sockets and networking. Because it runs in the kernel, any bug that can give users control of this driver opens the door to systemwide control.

What’s a Use-After-Free (UAF)?

A *use-after-free* bug occurs when a program tries to use memory after it has been freed. This is dangerous, because attackers can sometimes manipulate what gets placed into that memory slot, allowing code execution or privilege escalation.

Vulnerability Detail

CVE-2025-32709 exists in the way AFD.sys improperly manages an internal object for socket operations. A normal user can create a situation where an object is freed, but another thread or code path keeps a pointer to it. By quickly initiating a new operation or mapping, an attacker can control what data is at that memory location, leading to execution of attacker-controlled code—but in *kernel* mode.

The classic local privilege escalation (LPE) by UAF in kernel drivers follows these steps

1. Trigger the Free: Find a way to free a kernel object while handles or pointers to it still exist.
2. Allocate Controlled Data (Heap Spraying): Quickly fill that freed memory spot with attacker-controlled data (using kernel pools).

Trigger Use: Cause the driver to use the dangling pointer, now pointing into attacker data.

4. Hijack Privileges: Overwrite process privileges or token structure via the UAF and escalate privileges.

Here’s pseudocode showing the logic (not a weaponized exploit)

// Step 1: Create socket
SOCKET sock = socket(AF_INET, SOCK_STREAM, );

// Step 2: Trigger object free; specifics omitted for safety
IoctlTriggerUAF(sock);

// Step 3: Spray kernel pool to reclaim freed memory slot
for(int i = ; i < 10000; i++) {
    HANDLE h = CreateFileA("\\\\.\\Null", ...); 
    // or some other spraying method
    handles[i] = h;
}

// Step 4: Trigger use-after-free
IoctlUseDanglingPointer(sock);

// Step 5: Check if privileges elevated
if (IsSystem()) {
    printf("Exploit succeeded, you are SYSTEM!\n");
}

*(Note: This is *not* a working exploit. It simply demonstrates typical data flow.)*

References

- Microsoft Security Advisory (April 2025) *(official description and patches)*
- Original Security Researcher's Writeup (if made public)
- WinSock AFD.sys Internals *(great technical reference)*
- Wikipedia: Use-after-free

Mitigation

Microsoft has released patches for all supported Windows versions in April 2025. Apply the updates as soon as possible. Disabling unnecessary local admin rights for users on shared/public computers lessens the risk of successful exploitation.

Conclusion

CVE-2025-32709 is a potent reminder that kernel UAF bugs are still a major vector for local privilege escalation. The fact that this bug sits in AFD.sys means it impacts all recent versions of Windows, from servers to desktops. Local attackers (including malware) can quickly leap to SYSTEM if the box is unpatched.

If you administer Windows systems, update without delay.

*Author: RedTeamWriteup, April 2025.
Exclusive content for responsible research and awareness.*

Timeline

Published on: 05/13/2025 17:16:04 UTC
Last modified on: 05/29/2025 22:21:05 UTC