---

Microsoft Word is one of the world’s most widely used word processors, but with its popularity comes risks. In early 2025, a critical vulnerability surfaced: CVE-2025-27747. This flaw, involving a “use-after-free” bug, could let hackers run malicious code just by tricking someone into opening a tampered Word document. Let’s dive into what this bug means, how exploitation works, and walk through a realistic code snippet for proof-of-concept.

What is CVE-2025-27747?

At its core, CVE-2025-27747 is a “use-after-free” vulnerability found inside the memory handling logic of Microsoft Office Word (all supported Windows versions as of February 2025). Here’s the breakdown:

Attack Vector: Malicious file (usually a DOCX or RTF)

Use-after-free means the program tries to use an object in memory after it’s already been freed (released). If an attacker can control what memory gets reused, they can trick Word into executing dangerous code.

- Microsoft Security Advisory – CVE-2025-27747 (official)
- NIST National Vulnerability Database – Details
- Security Researcher’s Analysis (example)

How Does the Exploit Work?

Let’s say a hacker crafts a specially-designed Word document. This file, when opened, exploits a flaw in how Word manages certain embedded objects (like OLE or custom macros). The document might, for example:

Trigger destruction of that object prematurely (via a clever macro or a malformed XML tag).

3. Cause Word to reference that already-freed object—but now the spot in memory has been filled with attacker-controlled data!
4. Execute attacker’s code (Word mistakenly “runs” whatever is in the memory for that supposed object).

Proof-of-Concept Code

Below is simple pseudocode to help you understand what’s happening “under the hood.” This is *not* actual Word exploit code (since distributing true ransomware tools isn’t legal), but it shows the dangerous workflow:

// Simulated C-like pseudocode showing use-after-free scenario

// Step 1: Allocate an object
WordObject* obj = allocateWordObject();

// Step 2: Free the object early (malicious DOCX triggers this)
free(obj); // object memory is returned to OS

// Step 3: Reallocate memory for attacker's data (attacker controls this via crafted file)
char* evilBuffer = malloc(sizeof(WordObject));
strcpy(evilBuffer, attacker_payload); // e.g., shellcode to launch Calculator

// Step 4: Word tries to use the original object pointer (now points to attacker's content)
obj->DoSomething(); // This actually executes shellcode!

In a real DOCX exploit, the attacker places shellcode where the object was, often via embedded ActiveX, OLE, or scripting.

High-Level Exploit Example (Using VBA Macro)

Attackers often *pair* this vulnerability with a macro to trigger memory mismanagement. Here’s a simplified look:

Sub Document_Open()
    Dim x As Object
    Set x = ActiveDocument.Shapes(1)
    Set x = Nothing ' Frees the object, but reference lingers

    ' Attacker-crafted code: memory is replaced with payload
    Call CopyPayloadToMemoryLocationOf(x)
    ' Now Word will use the freed -and-controlled- memory!
End Sub

Note: Actual exploitation relies on undocumented memory hacks and knowledge of Office internals.

What is the Real Impact?

If successfully exploited, an attacker can gain full control of your system as your login user—sometimes enough to install ransomware, steal passwords, or pivot further into a company’s network.

Microsoft’s first advisories revealed that exploits have already been seen in the wild. That means real attackers are already using this bug!

Windows 10 and 11 systems

*Cloud-only users (Office for Web) appear less vulnerable but aren’t guaranteed immune.*

Go to Word and hit: File > Account > Update Options > Update Now

- Or download updates from Official Microsoft Update

Especially beware of attachments in email, Teams, or USB drives

Disable macros (set to "Disable all macros with notification" in Trust Center)

Conclusion

CVE-2025-27747 is a stark reminder that even trusted apps like Microsoft Word can hold dangerous secrets. For attackers, exploiting a use-after-free flaw is gold; for defenders, it’s a race to patch and raise awareness.

Stay alert, keep Office updated, and never trust documents from unknown senders—especially in 2025.

References

- Microsoft CVE-2025-27747
- NIST NVD: CVE-2025-27747
- Exploit Labs Blog: Word UAF Exploit

Timeline

Published on: 04/08/2025 18:16:04 UTC
Last modified on: 05/06/2025 17:03:05 UTC